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.TH LIBPNG 3 "December 29, 2016"
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.SH NAME
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libpng \- Portable Network Graphics (PNG) Reference Library 1.2.57
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.SH SYNOPSIS
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\fB
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#include <png.h>\fP
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\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
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\fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
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\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
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\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
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\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
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\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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\fBpng_structp png_create_read_struct_2(png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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\fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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\fBpng_structp png_create_write_struct_2(png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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\fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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\fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
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\fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
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\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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\fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
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\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
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\fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
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\fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
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\fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
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\fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
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\fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
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\fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
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\fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
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\fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
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\fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fB#if \fI!defined(PNG_1_0_X)
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\fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
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\fI\fB#endif
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\fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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\fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
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\fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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\fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
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\fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
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\fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
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\fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
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\fBpng_uint_32 png_get_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
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\fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_values\fP\fB);\fP
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\fB#if \fI!defined(PNG_1_0_X)
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\fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
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\fBpng_uint_32 png_get_uint_31 (png_bytep \fIbuf\fP\fB);\fP
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\fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
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\fI\fB#endif
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\fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
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\fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
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\fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
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\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
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\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
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\fBDEPRECATED void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
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\fBDEPRECATED void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
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\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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\fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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\fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
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\fBpng_voidp png_memcpy_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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\fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
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\fBpng_voidp png_memset_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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\fBDEPRECATED void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
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\fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
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\fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
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\fBvoid png_read_destroy (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_infop \fIend_info_ptr\fP\fB);\fP
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\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
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\fBDEPRECATED void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
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\fBDEPRECATED void png_read_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
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\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
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\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
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\fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
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\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fB#if \fI!defined(PNG_1_0_X)
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\fBpng_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
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\fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
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\fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
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\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
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\fI\fB#endif
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\fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
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\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
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\fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
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\fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
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\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
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\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
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\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
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\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
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\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
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\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
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\fBvoid png_set_dither (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_dither\fP\fB);\fP
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\fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
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\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_expand_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
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\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
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\fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
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\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
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\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
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\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
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\fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
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\fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
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\fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
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\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
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\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
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\fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
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\fBvoid png_set_mem_fn(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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\fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
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\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
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\fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
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\fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
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\fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
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\fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
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\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
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\fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
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\fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
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\fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_fixed_point \fP\fIred\fP\fB, png_fixed_point \fIgreen\fP\fB);\fP
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\fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
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\fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
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\fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
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\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
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\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
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\fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
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\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
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\fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
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\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
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\fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
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\fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_values\fP\fB);\fP
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\fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
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\fBvoid png_set_unknown_chunk_location(png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
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\fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
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\fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
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\fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
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\fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
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\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
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\fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
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\fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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\fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
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\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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\fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
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\fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
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\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
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\fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
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\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
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\fBDEPRECATED void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
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\fBDEPRECATED void png_write_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
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\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
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\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
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\fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
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\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
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\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
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.SH DESCRIPTION
|
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The
|
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.I libpng
|
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library supports encoding, decoding, and various manipulations of
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the Portable Network Graphics (PNG) format image files. It uses the
|
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.IR zlib(3)
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compression library.
|
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Following is a copy of the libpng.txt file that accompanies libpng.
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.SH LIBPNG.TXT
|
|
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libpng.txt - A description on how to use and modify libpng
|
|
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|
|
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libpng version 1.2.57 - December 29, 2016
|
|
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Updated and distributed by Glenn Randers-Pehrson
|
|
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<glennrp at users.sourceforge.net>
|
|
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Copyright (c) 1998-2014 Glenn Randers-Pehrson
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|
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This document is released under the libpng license.
|
|
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For conditions of distribution and use, see the disclaimer
|
|
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and license in png.h
|
|
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|
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Based on:
|
|
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|
|
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libpng versions 0.97, January 1998, through 1.2.57 - December 29, 2016
|
|
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Updated and distributed by Glenn Randers-Pehrson
|
|
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Copyright (c) 1998-2014 Glenn Randers-Pehrson
|
|
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|
|
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libpng 1.0 beta 6 version 0.96 May 28, 1997
|
|
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Updated and distributed by Andreas Dilger
|
|
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Copyright (c) 1996, 1997 Andreas Dilger
|
|
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|
|
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libpng 1.0 beta 2 - version 0.88 January 26, 1996
|
|
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For conditions of distribution and use, see copyright
|
|
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notice in png.h. Copyright (c) 1995, 1996 Guy Eric
|
|
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Schalnat, Group 42, Inc.
|
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|
|
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Updated/rewritten per request in the libpng FAQ
|
|
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Copyright (c) 1995, 1996 Frank J. T. Wojcik
|
|
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December 18, 1995 & January 20, 1996
|
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|
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.SH I. Introduction
|
|
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|
|
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This file describes how to use and modify the PNG reference library
|
|
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(known as libpng) for your own use. There are five sections to this
|
|
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file: introduction, structures, reading, writing, and modification and
|
|
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configuration notes for various special platforms. In addition to this
|
|
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file, example.c is a good starting point for using the library, as
|
|
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it is heavily commented and should include everything most people
|
|
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will need. We assume that libpng is already installed; see the
|
|
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INSTALL file for instructions on how to install libpng.
|
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|
|
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For examples of libpng usage, see the files "example.c", "pngtest.c",
|
|
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and the files in the "contrib" directory, all of which are included in
|
|
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the libpng distribution.
|
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|
|
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Libpng was written as a companion to the PNG specification, as a way
|
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of reducing the amount of time and effort it takes to support the PNG
|
|
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file format in application programs.
|
|
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|
|
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The PNG specification (second edition), November 2003, is available as
|
|
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a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
|
|
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|
|
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The W3C and ISO documents have identical technical content.
|
|
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|
|
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The PNG-1.2 specification is available at
|
|
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<http://png-mng.sourceforge.net/pub/png/spec/1.2/>.
|
|
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It is technically equivalent
|
|
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to the PNG specification (second edition) but has some additional material.
|
|
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|
|
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The PNG-1.0 specification is available as RFC 2083
|
|
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<http://png-mng.sourceforge.net/pub/png/spec/1.0/> and as a
|
|
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W3C Recommendation <http://www.w3.org/TR/REC-png-961001>.
|
|
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|
|
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Some additional chunks are described in the special-purpose public chunks
|
|
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documents at <http://www.libpng.org/pub/png/spec/register/>
|
|
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|
|
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Other information
|
|
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about PNG, and the latest version of libpng, can be found at the PNG home
|
|
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page, <http://www.libpng.org/pub/png/>.
|
|
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|
|
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Most users will not have to modify the library significantly; advanced
|
|
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users may want to modify it more. All attempts were made to make it as
|
|
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complete as possible, while keeping the code easy to understand.
|
|
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Currently, this library only supports C. Support for other languages
|
|
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is being considered.
|
|
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|
|
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Libpng has been designed to handle multiple sessions at one time,
|
|
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to be easily modifiable, to be portable to the vast majority of
|
|
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machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
|
|
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to use. The ultimate goal of libpng is to promote the acceptance of
|
|
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the PNG file format in whatever way possible. While there is still
|
|
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work to be done (see the TODO file), libpng should cover the
|
|
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majority of the needs of its users.
|
|
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|
|
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Libpng uses zlib for its compression and decompression of PNG files.
|
|
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Further information about zlib, and the latest version of zlib, can
|
|
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be found at the zlib home page, <http://zlib.net/>.
|
|
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The zlib compression utility is a general purpose utility that is
|
|
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useful for more than PNG files, and can be used without libpng.
|
|
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See the documentation delivered with zlib for more details.
|
|
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You can usually find the source files for the zlib utility wherever you
|
|
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find the libpng source files.
|
|
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|
|
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Libpng is thread safe, provided the threads are using different
|
|
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instances of the structures. Each thread should have its own
|
|
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png_struct and png_info instances, and thus its own image.
|
|
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Libpng does not protect itself against two threads using the
|
|
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same instance of a structure.
|
|
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|
|
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.SH II. Structures
|
|
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|
|
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There are two main structures that are important to libpng, png_struct
|
|
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and png_info. The first, png_struct, is an internal structure that
|
|
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will not, for the most part, be used by a user except as the first
|
|
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variable passed to every libpng function call.
|
|
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|
|
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The png_info structure is designed to provide information about the
|
|
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PNG file. At one time, the fields of png_info were intended to be
|
|
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directly accessible to the user. However, this tended to cause problems
|
|
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with applications using dynamically loaded libraries, and as a result
|
|
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a set of interface functions for png_info (the png_get_*() and png_set_*()
|
|
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functions) was developed. The fields of png_info are still available for
|
|
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older applications, but it is suggested that applications use the new
|
|
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interfaces if at all possible.
|
|
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0ba690 |
|
|
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Applications that do make direct access to the members of png_struct (except
|
|
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0ba690 |
for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
|
|
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0ba690 |
and applications that make direct access to the members of png_info must
|
|
Packit |
0ba690 |
be recompiled if they were compiled or loaded with libpng version 1.0.6,
|
|
Packit |
0ba690 |
in which the members were in a different order. In version 1.0.7, the
|
|
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0ba690 |
members of the png_info structure reverted to the old order, as they were
|
|
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0ba690 |
in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
|
|
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0ba690 |
structures are going to be hidden, and the contents of the structures will
|
|
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only be accessible through the png_get/png_set functions.
|
|
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0ba690 |
|
|
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The png.h header file is an invaluable reference for programming with libpng.
|
|
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0ba690 |
And while I'm on the topic, make sure you include the libpng header file:
|
|
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|
|
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#include <png.h>
|
|
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|
|
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.SH III. Reading
|
|
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0ba690 |
|
|
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We'll now walk you through the possible functions to call when reading
|
|
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in a PNG file sequentially, briefly explaining the syntax and purpose
|
|
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of each one. See example.c and png.h for more detail. While
|
|
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progressive reading is covered in the next section, you will still
|
|
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0ba690 |
need some of the functions discussed in this section to read a PNG
|
|
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0ba690 |
file.
|
|
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0ba690 |
|
|
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0ba690 |
.SS Setup
|
|
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|
|
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You will want to do the I/O initialization(*) before you get into libpng,
|
|
Packit |
0ba690 |
so if it doesn't work, you don't have much to undo. Of course, you
|
|
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will also want to insure that you are, in fact, dealing with a PNG
|
|
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0ba690 |
file. Libpng provides a simple check to see if a file is a PNG file.
|
|
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0ba690 |
To use it, pass in the first 1 to 8 bytes of the file to the function
|
|
Packit |
0ba690 |
png_sig_cmp(), and it will return 0 (false) if the bytes match the
|
|
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0ba690 |
corresponding bytes of the PNG signature, or nonzero (true) otherwise.
|
|
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Of course, the more bytes you pass in, the greater the accuracy of the
|
|
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0ba690 |
prediction.
|
|
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0ba690 |
|
|
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0ba690 |
If you are intending to keep the file pointer open for use in libpng,
|
|
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0ba690 |
you must ensure you don't read more than 8 bytes from the beginning
|
|
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0ba690 |
of the file, and you also have to make a call to png_set_sig_bytes()
|
|
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with the number of bytes you read from the beginning. Libpng will
|
|
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then only check the bytes (if any) that your program didn't read.
|
|
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0ba690 |
|
|
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(*): If you are not using the standard I/O functions, you will need
|
|
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0ba690 |
to replace them with custom functions. See the discussion under
|
|
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0ba690 |
Customizing libpng.
|
|
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0ba690 |
|
|
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0ba690 |
|
|
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0ba690 |
FILE *fp = fopen(file_name, "rb");
|
|
Packit |
0ba690 |
if (!fp)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
fread(header, 1, number, fp);
|
|
Packit |
0ba690 |
is_png = !png_sig_cmp(header, 0, number);
|
|
Packit |
0ba690 |
if (!is_png)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
return (NOT_PNG);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Next, png_struct and png_info need to be allocated and initialized. In
|
|
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0ba690 |
order to ensure that the size of these structures is correct even with a
|
|
Packit |
0ba690 |
dynamically linked libpng, there are functions to initialize and
|
|
Packit |
0ba690 |
allocate the structures. We also pass the library version, optional
|
|
Packit |
0ba690 |
pointers to error handling functions, and a pointer to a data struct for
|
|
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0ba690 |
use by the error functions, if necessary (the pointer and functions can
|
|
Packit |
0ba690 |
be NULL if the default error handlers are to be used). See the section
|
|
Packit |
0ba690 |
on Changes to Libpng below regarding the old initialization functions.
|
|
Packit |
0ba690 |
The structure allocation functions quietly return NULL if they fail to
|
|
Packit |
0ba690 |
create the structure, so your application should check for that.
|
|
Packit |
0ba690 |
|
|
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0ba690 |
png_structp png_ptr = png_create_read_struct
|
|
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0ba690 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
Packit |
0ba690 |
user_error_fn, user_warning_fn);
|
|
Packit |
0ba690 |
if (!png_ptr)
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_infop info_ptr = png_create_info_struct(png_ptr);
|
|
Packit |
0ba690 |
if (!info_ptr)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_destroy_read_struct(&png_ptr,
|
|
Packit |
0ba690 |
(png_infopp)NULL, (png_infopp)NULL);
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_infop end_info = png_create_info_struct(png_ptr);
|
|
Packit |
0ba690 |
if (!end_info)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
Packit |
0ba690 |
(png_infopp)NULL);
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you want to use your own memory allocation routines,
|
|
Packit |
0ba690 |
define PNG_USER_MEM_SUPPORTED and use
|
|
Packit |
0ba690 |
png_create_read_struct_2() instead of png_create_read_struct():
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_structp png_ptr = png_create_read_struct_2
|
|
Packit |
0ba690 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
Packit |
0ba690 |
user_error_fn, user_warning_fn, (png_voidp)
|
|
Packit |
0ba690 |
user_mem_ptr, user_malloc_fn, user_free_fn);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The error handling routines passed to png_create_read_struct()
|
|
Packit |
0ba690 |
and the memory alloc/free routines passed to png_create_struct_2()
|
|
Packit |
0ba690 |
are only necessary if you are not using the libpng supplied error
|
|
Packit |
0ba690 |
handling and memory alloc/free functions.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
When libpng encounters an error, it expects to longjmp back
|
|
Packit |
0ba690 |
to your routine. Therefore, you will need to call setjmp and pass
|
|
Packit |
0ba690 |
your png_jmpbuf(png_ptr). If you read the file from different
|
|
Packit |
0ba690 |
routines, you will need to update the jmpbuf field every time you enter
|
|
Packit |
0ba690 |
a new routine that will call a png_*() function.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
See your documentation of setjmp/longjmp for your compiler for more
|
|
Packit |
0ba690 |
information on setjmp/longjmp. See the discussion on libpng error
|
|
Packit |
0ba690 |
handling in the Customizing Libpng section below for more information
|
|
Packit |
0ba690 |
on the libpng error handling. If an error occurs, and libpng longjmp's
|
|
Packit |
0ba690 |
back to your setjmp, you will want to call png_destroy_read_struct() to
|
|
Packit |
0ba690 |
free any memory.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (setjmp(png_jmpbuf(png_ptr)))
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
Packit |
0ba690 |
&end_info);
|
|
Packit |
0ba690 |
fclose(fp);
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you would rather avoid the complexity of setjmp/longjmp issues,
|
|
Packit |
0ba690 |
you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
|
|
Packit |
0ba690 |
errors will result in a call to PNG_ABORT() which defaults to abort().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Now you need to set up the input code. The default for libpng is to
|
|
Packit |
0ba690 |
use the C function fread(). If you use this, you will need to pass a
|
|
Packit |
0ba690 |
valid FILE * in the function png_init_io(). Be sure that the file is
|
|
Packit |
0ba690 |
opened in binary mode. If you wish to handle reading data in another
|
|
Packit |
0ba690 |
way, you need not call the png_init_io() function, but you must then
|
|
Packit |
0ba690 |
implement the libpng I/O methods discussed in the Customizing Libpng
|
|
Packit |
0ba690 |
section below.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_init_io(png_ptr, fp);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you had previously opened the file and read any of the signature from
|
|
Packit |
0ba690 |
the beginning in order to see if this was a PNG file, you need to let
|
|
Packit |
0ba690 |
libpng know that there are some bytes missing from the start of the file.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_sig_bytes(png_ptr, number);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Setting up callback code
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You can set up a callback function to handle any unknown chunks in the
|
|
Packit |
0ba690 |
input stream. You must supply the function
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
read_chunk_callback(png_ptr ptr,
|
|
Packit |
0ba690 |
png_unknown_chunkp chunk);
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
/* The unknown chunk structure contains your
|
|
Packit |
0ba690 |
chunk data, along with similar data for any other
|
|
Packit |
0ba690 |
unknown chunks: */
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_byte name[5];
|
|
Packit |
0ba690 |
png_byte *data;
|
|
Packit |
0ba690 |
png_size_t size;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* Note that libpng has already taken care of
|
|
Packit |
0ba690 |
the CRC handling */
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* put your code here. Search for your chunk in the
|
|
Packit |
0ba690 |
unknown chunk structure, process it, and return one
|
|
Packit |
0ba690 |
of the following: */
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
return (\-n); /* chunk had an error */
|
|
Packit |
0ba690 |
return (0); /* did not recognize */
|
|
Packit |
0ba690 |
return (n); /* success */
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
(You can give your function another name that you like instead of
|
|
Packit |
0ba690 |
"read_chunk_callback")
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
To inform libpng about your function, use
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
|
|
Packit |
0ba690 |
read_chunk_callback);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This names not only the callback function, but also a user pointer that
|
|
Packit |
0ba690 |
you can retrieve with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_user_chunk_ptr(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you call the png_set_read_user_chunk_fn() function, then all unknown
|
|
Packit |
0ba690 |
chunks will be saved when read, in case your callback function will need
|
|
Packit |
0ba690 |
one or more of them. This behavior can be changed with the
|
|
Packit |
0ba690 |
png_set_keep_unknown_chunks() function, described below.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
At this point, you can set up a callback function that will be
|
|
Packit |
0ba690 |
called after each row has been read, which you can use to control
|
|
Packit |
0ba690 |
a progress meter or the like. It's demonstrated in pngtest.c.
|
|
Packit |
0ba690 |
You must supply a function
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
void read_row_callback(png_ptr ptr, png_uint_32 row,
|
|
Packit |
0ba690 |
int pass);
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
/* put your code here */
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
(You can give it another name that you like instead of "read_row_callback")
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
To inform libpng about your function, use
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_read_status_fn(png_ptr, read_row_callback);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Unknown-chunk handling
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Now you get to set the way the library processes unknown chunks in the
|
|
Packit |
0ba690 |
input PNG stream. Both known and unknown chunks will be read. Normal
|
|
Packit |
0ba690 |
behavior is that known chunks will be parsed into information in
|
|
Packit |
0ba690 |
various info_ptr members while unknown chunks will be discarded. This
|
|
Packit |
0ba690 |
behavior can be wasteful if your application will never use some known
|
|
Packit |
0ba690 |
chunk types. To change this, you can call:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_keep_unknown_chunks(png_ptr, keep,
|
|
Packit |
0ba690 |
chunk_list, num_chunks);
|
|
Packit |
0ba690 |
keep - 0: default unknown chunk handling
|
|
Packit |
0ba690 |
1: ignore; do not keep
|
|
Packit |
0ba690 |
2: keep only if safe-to-copy
|
|
Packit |
0ba690 |
3: keep even if unsafe-to-copy
|
|
Packit |
0ba690 |
You can use these definitions:
|
|
Packit |
0ba690 |
PNG_HANDLE_CHUNK_AS_DEFAULT 0
|
|
Packit |
0ba690 |
PNG_HANDLE_CHUNK_NEVER 1
|
|
Packit |
0ba690 |
PNG_HANDLE_CHUNK_IF_SAFE 2
|
|
Packit |
0ba690 |
PNG_HANDLE_CHUNK_ALWAYS 3
|
|
Packit |
0ba690 |
chunk_list - list of chunks affected (a byte string,
|
|
Packit |
0ba690 |
five bytes per chunk, NULL or '\0' if
|
|
Packit |
0ba690 |
num_chunks is 0)
|
|
Packit |
0ba690 |
num_chunks - number of chunks affected; if 0, all
|
|
Packit |
0ba690 |
unknown chunks are affected. If nonzero,
|
|
Packit |
0ba690 |
only the chunks in the list are affected
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Unknown chunks declared in this way will be saved as raw data onto a
|
|
Packit |
0ba690 |
list of png_unknown_chunk structures. If a chunk that is normally
|
|
Packit |
0ba690 |
known to libpng is named in the list, it will be handled as unknown,
|
|
Packit |
0ba690 |
according to the "keep" directive. If a chunk is named in successive
|
|
Packit |
0ba690 |
instances of png_set_keep_unknown_chunks(), the final instance will
|
|
Packit |
0ba690 |
take precedence. The IHDR and IEND chunks should not be named in
|
|
Packit |
0ba690 |
chunk_list; if they are, libpng will process them normally anyway.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Here is an example of the usage of png_set_keep_unknown_chunks(),
|
|
Packit |
0ba690 |
where the private "vpAg" chunk will later be processed by a user chunk
|
|
Packit |
0ba690 |
callback function:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
|
|
Packit |
0ba690 |
png_byte unused_chunks[]=
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
104, 73, 83, 84, (png_byte) '\0', /* hIST */
|
|
Packit |
0ba690 |
105, 84, 88, 116, (png_byte) '\0', /* iTXt */
|
|
Packit |
0ba690 |
112, 67, 65, 76, (png_byte) '\0', /* pCAL */
|
|
Packit |
0ba690 |
115, 67, 65, 76, (png_byte) '\0', /* sCAL */
|
|
Packit |
0ba690 |
115, 80, 76, 84, (png_byte) '\0', /* sPLT */
|
|
Packit |
0ba690 |
116, 73, 77, 69, (png_byte) '\0', /* tIME */
|
|
Packit |
0ba690 |
};
|
|
Packit |
0ba690 |
#endif
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
...
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
|
|
Packit |
0ba690 |
/* ignore all unknown chunks: */
|
|
Packit |
0ba690 |
png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
|
|
Packit |
0ba690 |
/* except for vpAg: */
|
|
Packit |
0ba690 |
png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
|
|
Packit |
0ba690 |
/* also ignore unused known chunks: */
|
|
Packit |
0ba690 |
png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
|
|
Packit |
0ba690 |
(int)sizeof(unused_chunks)/5);
|
|
Packit |
0ba690 |
#endif
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS User limits
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The PNG specification allows the width and height of an image to be as
|
|
Packit |
0ba690 |
large as 2^(31\-1 (0x7fffffff), or about 2.147 billion rows and columns.
|
|
Packit |
0ba690 |
Since very few applications really need to process such large images,
|
|
Packit |
0ba690 |
we have imposed an arbitrary 1-million limit on rows and columns.
|
|
Packit |
0ba690 |
Larger images will be rejected immediately with a png_error() call. If
|
|
Packit |
0ba690 |
you wish to override this limit, you can use
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_user_limits(png_ptr, width_max, height_max);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
to set your own limits, or use width_max = height_max = 0x7fffffffL
|
|
Packit |
0ba690 |
to allow all valid dimensions (libpng may reject some very large images
|
|
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0ba690 |
anyway because of potential buffer overflow conditions).
|
|
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0ba690 |
|
|
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0ba690 |
You should put this statement after you create the PNG structure and
|
|
Packit |
0ba690 |
before calling png_read_info(), png_read_png(), or png_process_data().
|
|
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0ba690 |
If you need to retrieve the limits that are being applied, use
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
width_max = png_get_user_width_max(png_ptr);
|
|
Packit |
0ba690 |
height_max = png_get_user_height_max(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The PNG specification sets no limit on the number of ancillary chunks
|
|
Packit |
0ba690 |
allowed in a PNG datastream. You can impose a limit on the total number
|
|
Packit |
0ba690 |
of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where 0x7fffffffL means unlimited. You can retrieve this limit with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
chunk_cache_max = png_get_chunk_cache_max(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This limit also applies to the number of buffers that can be allocated
|
|
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0ba690 |
by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS The high-level read interface
|
|
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0ba690 |
|
|
Packit |
0ba690 |
At this point there are two ways to proceed; through the high-level
|
|
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0ba690 |
read interface, or through a sequence of low-level read operations.
|
|
Packit |
0ba690 |
You can use the high-level interface if (a) you are willing to read
|
|
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0ba690 |
the entire image into memory, and (b) the input transformations
|
|
Packit |
0ba690 |
you want to do are limited to the following set:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG_TRANSFORM_IDENTITY No transformation
|
|
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0ba690 |
PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
|
|
Packit |
0ba690 |
8 bits
|
|
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0ba690 |
PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
|
|
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0ba690 |
PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
|
|
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0ba690 |
samples to bytes
|
|
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0ba690 |
PNG_TRANSFORM_PACKSWAP Change order of packed
|
|
Packit |
0ba690 |
pixels to LSB first
|
|
Packit |
0ba690 |
PNG_TRANSFORM_EXPAND Perform set_expand()
|
|
Packit |
0ba690 |
PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|
Packit |
0ba690 |
PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|
Packit |
0ba690 |
sBIT depth
|
|
Packit |
0ba690 |
PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|
Packit |
0ba690 |
to BGRA
|
|
Packit |
0ba690 |
PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|
Packit |
0ba690 |
to AG
|
|
Packit |
0ba690 |
PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|
Packit |
0ba690 |
to transparency
|
|
Packit |
0ba690 |
PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|
Packit |
0ba690 |
PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
|
|
Packit |
0ba690 |
to RGB (or GA to RGBA)
|
|
Packit |
0ba690 |
|
|
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0ba690 |
(This excludes setting a background color, doing gamma transformation,
|
|
Packit |
0ba690 |
dithering, and setting filler.) If this is the case, simply do this:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_read_png(png_ptr, info_ptr, png_transforms, NULL)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where png_transforms is an integer containing the bitwise OR of some
|
|
Packit |
0ba690 |
set of transformation flags. This call is equivalent to png_read_info(),
|
|
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0ba690 |
followed the set of transformations indicated by the transform mask,
|
|
Packit |
0ba690 |
then png_read_image(), and finally png_read_end().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
(The final parameter of this call is not yet used. Someday it might point
|
|
Packit |
0ba690 |
to transformation parameters required by some future input transform.)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You must use png_transforms and not call any png_set_transform() functions
|
|
Packit |
0ba690 |
when you use png_read_png().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
After you have called png_read_png(), you can retrieve the image data
|
|
Packit |
0ba690 |
with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
row_pointers = png_get_rows(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where row_pointers is an array of pointers to the pixel data for each row:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_bytep row_pointers[height];
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you know your image size and pixel size ahead of time, you can allocate
|
|
Packit |
0ba690 |
row_pointers prior to calling png_read_png() with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
|
|
Packit |
0ba690 |
png_error (png_ptr,
|
|
Packit |
0ba690 |
"Image is too tall to process in memory");
|
|
Packit |
0ba690 |
if (width > PNG_UINT_32_MAX/pixel_size)
|
|
Packit |
0ba690 |
png_error (png_ptr,
|
|
Packit |
0ba690 |
"Image is too wide to process in memory");
|
|
Packit |
0ba690 |
row_pointers = png_malloc(png_ptr,
|
|
Packit |
0ba690 |
height*png_sizeof(png_bytep));
|
|
Packit |
0ba690 |
for (int i=0; i
|
|
Packit |
0ba690 |
row_pointers[i]=NULL; /* security precaution */
|
|
Packit |
0ba690 |
for (int i=0; i
|
|
Packit |
0ba690 |
row_pointers[i]=png_malloc(png_ptr,
|
|
Packit |
0ba690 |
width*pixel_size);
|
|
Packit |
0ba690 |
png_set_rows(png_ptr, info_ptr, &row_pointers);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Alternatively you could allocate your image in one big block and define
|
|
Packit |
0ba690 |
row_pointers[i] to point into the proper places in your block.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you use png_set_rows(), the application is responsible for freeing
|
|
Packit |
0ba690 |
row_pointers (and row_pointers[i], if they were separately allocated).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you don't allocate row_pointers ahead of time, png_read_png() will
|
|
Packit |
0ba690 |
do it, and it'll be free'ed when you call png_destroy_*().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS The low-level read interface
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are going the low-level route, you are now ready to read all
|
|
Packit |
0ba690 |
the file information up to the actual image data. You do this with a
|
|
Packit |
0ba690 |
call to png_read_info().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_read_info(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This will process all chunks up to but not including the image data.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Querying the info structure
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Functions are used to get the information from the info_ptr once it
|
|
Packit |
0ba690 |
has been read. Note that these fields may not be completely filled
|
|
Packit |
0ba690 |
in until png_read_end() has read the chunk data following the image.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_IHDR(png_ptr, info_ptr, &width, &height,
|
|
Packit |
0ba690 |
&bit_depth, &color_type, &interlace_type,
|
|
Packit |
0ba690 |
&compression_type, &filter_method);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
width - holds the width of the image
|
|
Packit |
0ba690 |
in pixels (up to 2^31).
|
|
Packit |
0ba690 |
height - holds the height of the image
|
|
Packit |
0ba690 |
in pixels (up to 2^31).
|
|
Packit |
0ba690 |
bit_depth - holds the bit depth of one of the
|
|
Packit |
0ba690 |
image channels. (valid values are
|
|
Packit |
0ba690 |
1, 2, 4, 8, 16 and depend also on
|
|
Packit |
0ba690 |
the color_type. See also
|
|
Packit |
0ba690 |
significant bits (sBIT) below).
|
|
Packit |
0ba690 |
color_type - describes which color/alpha channels
|
|
Packit |
0ba690 |
are present.
|
|
Packit |
0ba690 |
PNG_COLOR_TYPE_GRAY
|
|
Packit |
0ba690 |
(bit depths 1, 2, 4, 8, 16)
|
|
Packit |
0ba690 |
PNG_COLOR_TYPE_GRAY_ALPHA
|
|
Packit |
0ba690 |
(bit depths 8, 16)
|
|
Packit |
0ba690 |
PNG_COLOR_TYPE_PALETTE
|
|
Packit |
0ba690 |
(bit depths 1, 2, 4, 8)
|
|
Packit |
0ba690 |
PNG_COLOR_TYPE_RGB
|
|
Packit |
0ba690 |
(bit_depths 8, 16)
|
|
Packit |
0ba690 |
PNG_COLOR_TYPE_RGB_ALPHA
|
|
Packit |
0ba690 |
(bit_depths 8, 16)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG_COLOR_MASK_PALETTE
|
|
Packit |
0ba690 |
PNG_COLOR_MASK_COLOR
|
|
Packit |
0ba690 |
PNG_COLOR_MASK_ALPHA
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
filter_method - (must be PNG_FILTER_TYPE_BASE
|
|
Packit |
0ba690 |
for PNG 1.0, and can also be
|
|
Packit |
0ba690 |
PNG_INTRAPIXEL_DIFFERENCING if
|
|
Packit |
0ba690 |
the PNG datastream is embedded in
|
|
Packit |
0ba690 |
a MNG-1.0 datastream)
|
|
Packit |
0ba690 |
compression_type - (must be PNG_COMPRESSION_TYPE_BASE
|
|
Packit |
0ba690 |
for PNG 1.0)
|
|
Packit |
0ba690 |
interlace_type - (PNG_INTERLACE_NONE or
|
|
Packit |
0ba690 |
PNG_INTERLACE_ADAM7)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Any or all of interlace_type, compression_type, or
|
|
Packit |
0ba690 |
filter_method can be NULL if you are
|
|
Packit |
0ba690 |
not interested in their values.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Note that png_get_IHDR() returns 32-bit data into
|
|
Packit |
0ba690 |
the application's width and height variables.
|
|
Packit |
0ba690 |
This is an unsafe situation if these are 16-bit
|
|
Packit |
0ba690 |
variables. In such situations, the
|
|
Packit |
0ba690 |
png_get_image_width() and png_get_image_height()
|
|
Packit |
0ba690 |
functions described below are safer.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
width = png_get_image_width(png_ptr,
|
|
Packit |
0ba690 |
info_ptr);
|
|
Packit |
0ba690 |
height = png_get_image_height(png_ptr,
|
|
Packit |
0ba690 |
info_ptr);
|
|
Packit |
0ba690 |
bit_depth = png_get_bit_depth(png_ptr,
|
|
Packit |
0ba690 |
info_ptr);
|
|
Packit |
0ba690 |
color_type = png_get_color_type(png_ptr,
|
|
Packit |
0ba690 |
info_ptr);
|
|
Packit |
0ba690 |
filter_method = png_get_filter_type(png_ptr,
|
|
Packit |
0ba690 |
info_ptr);
|
|
Packit |
0ba690 |
compression_type = png_get_compression_type(png_ptr,
|
|
Packit |
0ba690 |
info_ptr);
|
|
Packit |
0ba690 |
interlace_type = png_get_interlace_type(png_ptr,
|
|
Packit |
0ba690 |
info_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
channels = png_get_channels(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
channels - number of channels of info for the
|
|
Packit |
0ba690 |
color type (valid values are 1 (GRAY,
|
|
Packit |
0ba690 |
PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
|
|
Packit |
0ba690 |
4 (RGB_ALPHA or RGB + filler byte))
|
|
Packit |
0ba690 |
rowbytes = png_get_rowbytes(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
rowbytes - number of bytes needed to hold a row
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
signature = png_get_signature(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
signature - holds the signature read from the
|
|
Packit |
0ba690 |
file (if any). The data is kept in
|
|
Packit |
0ba690 |
the same offset it would be if the
|
|
Packit |
0ba690 |
whole signature were read (i.e. if an
|
|
Packit |
0ba690 |
application had already read in 4
|
|
Packit |
0ba690 |
bytes of signature before starting
|
|
Packit |
0ba690 |
libpng, the remaining 4 bytes would
|
|
Packit |
0ba690 |
be in signature[4] through signature[7]
|
|
Packit |
0ba690 |
(see png_set_sig_bytes())).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
These are also important, but their validity depends on whether the chunk
|
|
Packit |
0ba690 |
has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
|
|
Packit |
0ba690 |
png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
|
|
Packit |
0ba690 |
data has been read, or zero if it is missing. The parameters to the
|
|
Packit |
0ba690 |
png_get_<chunk> are set directly if they are simple data types, or a
|
|
Packit |
0ba690 |
pointer into the info_ptr is returned for any complex types.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_PLTE(png_ptr, info_ptr, &palette,
|
|
Packit |
0ba690 |
&num_palette);
|
|
Packit |
0ba690 |
palette - the palette for the file
|
|
Packit |
0ba690 |
(array of png_color)
|
|
Packit |
0ba690 |
num_palette - number of entries in the palette
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_gAMA(png_ptr, info_ptr, &gamma);
|
|
Packit |
0ba690 |
gamma - the gamma the file is written
|
|
Packit |
0ba690 |
at (PNG_INFO_gAMA)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
|
|
Packit |
0ba690 |
srgb_intent - the rendering intent (PNG_INFO_sRGB)
|
|
Packit |
0ba690 |
The presence of the sRGB chunk
|
|
Packit |
0ba690 |
means that the pixel data is in the
|
|
Packit |
0ba690 |
sRGB color space. This chunk also
|
|
Packit |
0ba690 |
implies specific values of gAMA and
|
|
Packit |
0ba690 |
cHRM.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_iCCP(png_ptr, info_ptr, &name,
|
|
Packit |
0ba690 |
&compression_type, &profile, &proflen);
|
|
Packit |
0ba690 |
name - The profile name.
|
|
Packit |
0ba690 |
compression - The compression type; always
|
|
Packit |
0ba690 |
PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|
Packit |
0ba690 |
You may give NULL to this argument to
|
|
Packit |
0ba690 |
ignore it.
|
|
Packit |
0ba690 |
profile - International Color Consortium color
|
|
Packit |
0ba690 |
profile data. May contain NULs.
|
|
Packit |
0ba690 |
proflen - length of profile data in bytes.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_sBIT(png_ptr, info_ptr, &sig_bit);
|
|
Packit |
0ba690 |
sig_bit - the number of significant bits for
|
|
Packit |
0ba690 |
(PNG_INFO_sBIT) each of the gray,
|
|
Packit |
0ba690 |
red, green, and blue channels,
|
|
Packit |
0ba690 |
whichever are appropriate for the
|
|
Packit |
0ba690 |
given color type (png_color_16)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
|
|
Packit |
0ba690 |
&trans_values);
|
|
Packit |
0ba690 |
trans - array of transparent
|
|
Packit |
0ba690 |
entries for palette (PNG_INFO_tRNS)
|
|
Packit |
0ba690 |
trans_values - graylevel or color sample values of
|
|
Packit |
0ba690 |
the single transparent color for
|
|
Packit |
0ba690 |
non-paletted images (PNG_INFO_tRNS)
|
|
Packit |
0ba690 |
num_trans - number of transparent entries
|
|
Packit |
0ba690 |
(PNG_INFO_tRNS)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_hIST(png_ptr, info_ptr, &hist);
|
|
Packit |
0ba690 |
(PNG_INFO_hIST)
|
|
Packit |
0ba690 |
hist - histogram of palette (array of
|
|
Packit |
0ba690 |
png_uint_16)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_tIME(png_ptr, info_ptr, &mod_time);
|
|
Packit |
0ba690 |
mod_time - time image was last modified
|
|
Packit |
0ba690 |
(PNG_VALID_tIME)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_bKGD(png_ptr, info_ptr, &background);
|
|
Packit |
0ba690 |
background - background color (PNG_VALID_bKGD)
|
|
Packit |
0ba690 |
valid 16-bit red, green and blue
|
|
Packit |
0ba690 |
values, regardless of color_type
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
num_comments = png_get_text(png_ptr, info_ptr,
|
|
Packit |
0ba690 |
&text_ptr, &num_text);
|
|
Packit |
0ba690 |
num_comments - number of comments
|
|
Packit |
0ba690 |
text_ptr - array of png_text holding image
|
|
Packit |
0ba690 |
comments
|
|
Packit |
0ba690 |
text_ptr[i].compression - type of compression used
|
|
Packit |
0ba690 |
on "text" PNG_TEXT_COMPRESSION_NONE
|
|
Packit |
0ba690 |
PNG_TEXT_COMPRESSION_zTXt
|
|
Packit |
0ba690 |
PNG_ITXT_COMPRESSION_NONE
|
|
Packit |
0ba690 |
PNG_ITXT_COMPRESSION_zTXt
|
|
Packit |
0ba690 |
text_ptr[i].key - keyword for comment. Must contain
|
|
Packit |
0ba690 |
1-79 characters.
|
|
Packit |
0ba690 |
text_ptr[i].text - text comments for current
|
|
Packit |
0ba690 |
keyword. Can be empty.
|
|
Packit |
0ba690 |
text_ptr[i].text_length - length of text string,
|
|
Packit |
0ba690 |
after decompression, 0 for iTXt
|
|
Packit |
0ba690 |
text_ptr[i].itxt_length - length of itxt string,
|
|
Packit |
0ba690 |
after decompression, 0 for tEXt/zTXt
|
|
Packit |
0ba690 |
text_ptr[i].lang - language of comment (empty
|
|
Packit |
0ba690 |
string for unknown).
|
|
Packit |
0ba690 |
text_ptr[i].lang_key - keyword in UTF-8
|
|
Packit |
0ba690 |
(empty string for unknown).
|
|
Packit |
0ba690 |
Note that the itxt_length, lang, and lang_key
|
|
Packit |
0ba690 |
members of the text_ptr structure only exist
|
|
Packit |
0ba690 |
when the library is built with iTXt chunk support.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
num_text - number of comments (same as
|
|
Packit |
0ba690 |
num_comments; you can put NULL here
|
|
Packit |
0ba690 |
to avoid the duplication)
|
|
Packit |
0ba690 |
Note while png_set_text() will accept text, language,
|
|
Packit |
0ba690 |
and translated keywords that can be NULL pointers, the
|
|
Packit |
0ba690 |
structure returned by png_get_text will always contain
|
|
Packit |
0ba690 |
regular zero-terminated C strings. They might be
|
|
Packit |
0ba690 |
empty strings but they will never be NULL pointers.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
num_spalettes = png_get_sPLT(png_ptr, info_ptr,
|
|
Packit |
0ba690 |
&palette_ptr);
|
|
Packit |
0ba690 |
palette_ptr - array of palette structures holding
|
|
Packit |
0ba690 |
contents of one or more sPLT chunks
|
|
Packit |
0ba690 |
read.
|
|
Packit |
0ba690 |
num_spalettes - number of sPLT chunks read.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
|
|
Packit |
0ba690 |
&unit_type);
|
|
Packit |
0ba690 |
offset_x - positive offset from the left edge
|
|
Packit |
0ba690 |
of the screen
|
|
Packit |
0ba690 |
offset_y - positive offset from the top edge
|
|
Packit |
0ba690 |
of the screen
|
|
Packit |
0ba690 |
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
|
|
Packit |
0ba690 |
&unit_type);
|
|
Packit |
0ba690 |
res_x - pixels/unit physical resolution in
|
|
Packit |
0ba690 |
x direction
|
|
Packit |
0ba690 |
res_y - pixels/unit physical resolution in
|
|
Packit |
0ba690 |
x direction
|
|
Packit |
0ba690 |
unit_type - PNG_RESOLUTION_UNKNOWN,
|
|
Packit |
0ba690 |
PNG_RESOLUTION_METER
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_sCAL(png_ptr, info_ptr, &unit, &width,
|
|
Packit |
0ba690 |
&height)
|
|
Packit |
0ba690 |
unit - physical scale units (an integer)
|
|
Packit |
0ba690 |
width - width of a pixel in physical scale units
|
|
Packit |
0ba690 |
height - height of a pixel in physical scale units
|
|
Packit |
0ba690 |
(width and height are doubles)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
|
|
Packit |
0ba690 |
&height)
|
|
Packit |
0ba690 |
unit - physical scale units (an integer)
|
|
Packit |
0ba690 |
width - width of a pixel in physical scale units
|
|
Packit |
0ba690 |
height - height of a pixel in physical scale units
|
|
Packit |
0ba690 |
(width and height are strings like "2.54")
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
num_unknown_chunks = png_get_unknown_chunks(png_ptr,
|
|
Packit |
0ba690 |
info_ptr, &unknowns)
|
|
Packit |
0ba690 |
unknowns - array of png_unknown_chunk
|
|
Packit |
0ba690 |
structures holding unknown chunks
|
|
Packit |
0ba690 |
unknowns[i].name - name of unknown chunk
|
|
Packit |
0ba690 |
unknowns[i].data - data of unknown chunk
|
|
Packit |
0ba690 |
unknowns[i].size - size of unknown chunk's data
|
|
Packit |
0ba690 |
unknowns[i].location - position of chunk in file
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The value of "i" corresponds to the order in which the
|
|
Packit |
0ba690 |
chunks were read from the PNG file or inserted with the
|
|
Packit |
0ba690 |
png_set_unknown_chunks() function.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The data from the pHYs chunk can be retrieved in several convenient
|
|
Packit |
0ba690 |
forms:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
res_x = png_get_x_pixels_per_meter(png_ptr,
|
|
Packit |
0ba690 |
info_ptr)
|
|
Packit |
0ba690 |
res_y = png_get_y_pixels_per_meter(png_ptr,
|
|
Packit |
0ba690 |
info_ptr)
|
|
Packit |
0ba690 |
res_x_and_y = png_get_pixels_per_meter(png_ptr,
|
|
Packit |
0ba690 |
info_ptr)
|
|
Packit |
0ba690 |
res_x = png_get_x_pixels_per_inch(png_ptr,
|
|
Packit |
0ba690 |
info_ptr)
|
|
Packit |
0ba690 |
res_y = png_get_y_pixels_per_inch(png_ptr,
|
|
Packit |
0ba690 |
info_ptr)
|
|
Packit |
0ba690 |
res_x_and_y = png_get_pixels_per_inch(png_ptr,
|
|
Packit |
0ba690 |
info_ptr)
|
|
Packit |
0ba690 |
aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
|
|
Packit |
0ba690 |
info_ptr)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
(Each of these returns 0 [signifying "unknown"] if
|
|
Packit |
0ba690 |
the data is not present or if res_x is 0;
|
|
Packit |
0ba690 |
res_x_and_y is 0 if res_x != res_y)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The data from the oFFs chunk can be retrieved in several convenient
|
|
Packit |
0ba690 |
forms:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
(Each of these returns 0 [signifying "unknown" if both
|
|
Packit |
0ba690 |
x and y are 0] if the data is not present or if the
|
|
Packit |
0ba690 |
chunk is present but the unit is the pixel)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
For more information, see the png_info definition in png.h and the
|
|
Packit |
0ba690 |
PNG specification for chunk contents. Be careful with trusting
|
|
Packit |
0ba690 |
rowbytes, as some of the transformations could increase the space
|
|
Packit |
0ba690 |
needed to hold a row (expand, filler, gray_to_rgb, etc.).
|
|
Packit |
0ba690 |
See png_read_update_info(), below.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
A quick word about text_ptr and num_text. PNG stores comments in
|
|
Packit |
0ba690 |
keyword/text pairs, one pair per chunk, with no limit on the number
|
|
Packit |
0ba690 |
of text chunks, and a 2^31 byte limit on their size. While there are
|
|
Packit |
0ba690 |
suggested keywords, there is no requirement to restrict the use to these
|
|
Packit |
0ba690 |
strings. It is strongly suggested that keywords and text be sensible
|
|
Packit |
0ba690 |
to humans (that's the point), so don't use abbreviations. Non-printing
|
|
Packit |
0ba690 |
symbols are not allowed. See the PNG specification for more details.
|
|
Packit |
0ba690 |
There is also no requirement to have text after the keyword.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Keywords should be limited to 79 Latin-1 characters without leading or
|
|
Packit |
0ba690 |
trailing spaces, but non-consecutive spaces are allowed within the
|
|
Packit |
0ba690 |
keyword. It is possible to have the same keyword any number of times.
|
|
Packit |
0ba690 |
The text_ptr is an array of png_text structures, each holding a
|
|
Packit |
0ba690 |
pointer to a language string, a pointer to a keyword and a pointer to
|
|
Packit |
0ba690 |
a text string. The text string, language code, and translated
|
|
Packit |
0ba690 |
keyword may be empty or NULL pointers. The keyword/text
|
|
Packit |
0ba690 |
pairs are put into the array in the order that they are received.
|
|
Packit |
0ba690 |
However, some or all of the text chunks may be after the image, so, to
|
|
Packit |
0ba690 |
make sure you have read all the text chunks, don't mess with these
|
|
Packit |
0ba690 |
until after you read the stuff after the image. This will be
|
|
Packit |
0ba690 |
mentioned again below in the discussion that goes with png_read_end().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Input transformations
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
After you've read the header information, you can set up the library
|
|
Packit |
0ba690 |
to handle any special transformations of the image data. The various
|
|
Packit |
0ba690 |
ways to transform the data will be described in the order that they
|
|
Packit |
0ba690 |
should occur. This is important, as some of these change the color
|
|
Packit |
0ba690 |
type and/or bit depth of the data, and some others only work on
|
|
Packit |
0ba690 |
certain color types and bit depths. Even though each transformation
|
|
Packit |
0ba690 |
checks to see if it has data that it can do something with, you should
|
|
Packit |
0ba690 |
make sure to only enable a transformation if it will be valid for the
|
|
Packit |
0ba690 |
data. For example, don't swap red and blue on grayscale data.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The colors used for the background and transparency values should be
|
|
Packit |
0ba690 |
supplied in the same format/depth as the current image data. They
|
|
Packit |
0ba690 |
are stored in the same format/depth as the image data in a bKGD or tRNS
|
|
Packit |
0ba690 |
chunk, so this is what libpng expects for this data. The colors are
|
|
Packit |
0ba690 |
transformed to keep in sync with the image data when an application
|
|
Packit |
0ba690 |
calls the png_read_update_info() routine (see below).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Data will be decoded into the supplied row buffers packed into bytes
|
|
Packit |
0ba690 |
unless the library has been told to transform it into another format.
|
|
Packit |
0ba690 |
For example, 4 bit/pixel paletted or grayscale data will be returned
|
|
Packit |
0ba690 |
2 pixels/byte with the leftmost pixel in the high-order bits of the
|
|
Packit |
0ba690 |
byte, unless png_set_packing() is called. 8-bit RGB data will be stored
|
|
Packit |
0ba690 |
in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
|
|
Packit |
0ba690 |
is called to insert filler bytes, either before or after each RGB triplet.
|
|
Packit |
0ba690 |
16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
|
|
Packit |
0ba690 |
byte of the color value first, unless png_set_strip_16() is called to
|
|
Packit |
0ba690 |
transform it to regular RGB RGB triplets, or png_set_filler() or
|
|
Packit |
0ba690 |
png_set_add alpha() is called to insert filler bytes, either before or
|
|
Packit |
0ba690 |
after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
|
|
Packit |
0ba690 |
be modified with
|
|
Packit |
0ba690 |
png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The following code transforms grayscale images of less than 8 to 8 bits,
|
|
Packit |
0ba690 |
changes paletted images to RGB, and adds a full alpha channel if there is
|
|
Packit |
0ba690 |
transparency information in a tRNS chunk. This is most useful on
|
|
Packit |
0ba690 |
grayscale images with bit depths of 2 or 4 or if there is a multiple-image
|
|
Packit |
0ba690 |
viewing application that wishes to treat all images in the same way.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type == PNG_COLOR_TYPE_PALETTE)
|
|
Packit |
0ba690 |
png_set_palette_to_rgb(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type == PNG_COLOR_TYPE_GRAY &&
|
|
Packit |
0ba690 |
bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (png_get_valid(png_ptr, info_ptr,
|
|
Packit |
0ba690 |
PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
These three functions are actually aliases for png_set_expand(), added
|
|
Packit |
0ba690 |
in libpng version 1.0.4, with the function names expanded to improve code
|
|
Packit |
0ba690 |
readability. In some future version they may actually do different
|
|
Packit |
0ba690 |
things.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
|
|
Packit |
0ba690 |
added. It expands the sample depth without changing tRNS to alpha.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
As of libpng version 1.2.57, not all possible expansions are supported.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
In the following table, the 01 means grayscale with depth<8, 31 means
|
|
Packit |
0ba690 |
indexed with depth<8, other numerals represent the color type, "T" means
|
|
Packit |
0ba690 |
the tRNS chunk is present, A means an alpha channel is present, and O
|
|
Packit |
0ba690 |
means tRNS or alpha is present but all pixels in the image are opaque.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
|
|
Packit |
0ba690 |
TO
|
|
Packit |
0ba690 |
01 -
|
|
Packit |
0ba690 |
31 -
|
|
Packit |
0ba690 |
0 1 -
|
|
Packit |
0ba690 |
0T -
|
|
Packit |
0ba690 |
0O -
|
|
Packit |
0ba690 |
2 GX -
|
|
Packit |
0ba690 |
2T -
|
|
Packit |
0ba690 |
2O -
|
|
Packit |
0ba690 |
3 1 -
|
|
Packit |
0ba690 |
3T -
|
|
Packit |
0ba690 |
3O -
|
|
Packit |
0ba690 |
4A T -
|
|
Packit |
0ba690 |
4O -
|
|
Packit |
0ba690 |
6A GX TX TX -
|
|
Packit |
0ba690 |
6O GX TX -
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Within the matrix,
|
|
Packit |
0ba690 |
"-" means the transformation is not supported.
|
|
Packit |
0ba690 |
"X" means the transformation is obtained by png_set_expand().
|
|
Packit |
0ba690 |
"1" means the transformation is obtained by
|
|
Packit |
0ba690 |
png_set_expand_gray_1_2_4_to_8
|
|
Packit |
0ba690 |
"G" means the transformation is obtained by
|
|
Packit |
0ba690 |
png_set_gray_to_rgb().
|
|
Packit |
0ba690 |
"P" means the transformation is obtained by
|
|
Packit |
0ba690 |
png_set_expand_palette_to_rgb().
|
|
Packit |
0ba690 |
"T" means the transformation is obtained by
|
|
Packit |
0ba690 |
png_set_tRNS_to_alpha().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG can have files with 16 bits per channel. If you only can handle
|
|
Packit |
0ba690 |
8 bits per channel, this will strip the pixels down to 8 bit.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (bit_depth == 16)
|
|
Packit |
0ba690 |
png_set_strip_16(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If, for some reason, you don't need the alpha channel on an image,
|
|
Packit |
0ba690 |
and you want to remove it rather than combining it with the background
|
|
Packit |
0ba690 |
(but the image author certainly had in mind that you *would* combine
|
|
Packit |
0ba690 |
it with the background, so that's what you should probably do):
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type & PNG_COLOR_MASK_ALPHA)
|
|
Packit |
0ba690 |
png_set_strip_alpha(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
In PNG files, the alpha channel in an image
|
|
Packit |
0ba690 |
is the level of opacity. If you need the alpha channel in an image to
|
|
Packit |
0ba690 |
be the level of transparency instead of opacity, you can invert the
|
|
Packit |
0ba690 |
alpha channel (or the tRNS chunk data) after it's read, so that 0 is
|
|
Packit |
0ba690 |
fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
|
|
Packit |
0ba690 |
images) is fully transparent, with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_invert_alpha(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The PNG format only supports pixels with postmultiplied alpha.
|
|
Packit |
0ba690 |
If you want to replace the pixels, after reading them, with pixels
|
|
Packit |
0ba690 |
that have premultiplied color samples, you can do this with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_premultiply_alpha(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you do this, any input with a tRNS chunk will be expanded to
|
|
Packit |
0ba690 |
have an alpha channel.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|
Packit |
0ba690 |
they can, resulting in, for example, 8 pixels per byte for 1 bit
|
|
Packit |
0ba690 |
files. This code expands to 1 pixel per byte without changing the
|
|
Packit |
0ba690 |
values of the pixels:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (bit_depth < 8)
|
|
Packit |
0ba690 |
png_set_packing(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
|
|
Packit |
0ba690 |
stored in a PNG image have been "scaled" or "shifted" up to the next
|
|
Packit |
0ba690 |
higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
|
|
Packit |
0ba690 |
to 8 bits/sample in the range [0, 255]). However, it is also possible
|
|
Packit |
0ba690 |
to convert the PNG pixel data back to the original bit depth of the
|
|
Packit |
0ba690 |
image. This call reduces the pixels back down to the original bit depth:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_color_8p sig_bit;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
|
|
Packit |
0ba690 |
png_set_shift(png_ptr, sig_bit);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files store 3-color pixels in red, green, blue order. This code
|
|
Packit |
0ba690 |
changes the storage of the pixels to blue, green, red:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type == PNG_COLOR_TYPE_RGB ||
|
|
Packit |
0ba690 |
color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|
Packit |
0ba690 |
png_set_bgr(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
|
|
Packit |
0ba690 |
into 4 or 8 bytes for windowing systems that need them in this format:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type == PNG_COLOR_TYPE_RGB)
|
|
Packit |
0ba690 |
png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where "filler" is the 8 or 16-bit number to fill with, and the location is
|
|
Packit |
0ba690 |
either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
|
|
Packit |
0ba690 |
you want the filler before the RGB or after. This transformation
|
|
Packit |
0ba690 |
does not affect images that already have full alpha channels. To add an
|
|
Packit |
0ba690 |
opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
|
|
Packit |
0ba690 |
will generate RGBA pixels.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Note that png_set_filler() does not change the color type. If you want
|
|
Packit |
0ba690 |
to do that, you can add a true alpha channel with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type == PNG_COLOR_TYPE_RGB ||
|
|
Packit |
0ba690 |
color_type == PNG_COLOR_TYPE_GRAY)
|
|
Packit |
0ba690 |
png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where "filler" contains the alpha value to assign to each pixel.
|
|
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0ba690 |
This function was added in libpng-1.2.7.
|
|
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0ba690 |
|
|
Packit |
0ba690 |
If you are reading an image with an alpha channel, and you need the
|
|
Packit |
0ba690 |
data as ARGB instead of the normal PNG format RGBA:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|
Packit |
0ba690 |
png_set_swap_alpha(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
For some uses, you may want a grayscale image to be represented as
|
|
Packit |
0ba690 |
RGB. This code will do that conversion:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|
Packit |
0ba690 |
color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|
Packit |
0ba690 |
png_set_gray_to_rgb(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
|
|
Packit |
0ba690 |
with alpha.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type == PNG_COLOR_TYPE_RGB ||
|
|
Packit |
0ba690 |
color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|
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0ba690 |
png_set_rgb_to_gray_fixed(png_ptr, error_action,
|
|
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0ba690 |
int red_weight, int green_weight);
|
|
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0ba690 |
|
|
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0ba690 |
error_action = 1: silently do the conversion
|
|
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0ba690 |
error_action = 2: issue a warning if the original
|
|
Packit |
0ba690 |
image has any pixel where
|
|
Packit |
0ba690 |
red != green or red != blue
|
|
Packit |
0ba690 |
error_action = 3: issue an error and abort the
|
|
Packit |
0ba690 |
conversion if the original
|
|
Packit |
0ba690 |
image has any pixel where
|
|
Packit |
0ba690 |
red != green or red != blue
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
red_weight: weight of red component times 100000
|
|
Packit |
0ba690 |
green_weight: weight of green component times 100000
|
|
Packit |
0ba690 |
If either weight is negative, default
|
|
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0ba690 |
weights (21268, 71514) are used.
|
|
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0ba690 |
|
|
Packit |
0ba690 |
If you have set error_action = 1 or 2, you can
|
|
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0ba690 |
later check whether the image really was gray, after processing
|
|
Packit |
0ba690 |
the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
|
|
Packit |
0ba690 |
It will return a png_byte that is zero if the image was gray or
|
|
Packit |
0ba690 |
1 if there were any non-gray pixels. bKGD and sBIT data
|
|
Packit |
0ba690 |
will be silently converted to grayscale, using the green channel
|
|
Packit |
0ba690 |
data, regardless of the error_action setting.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
With red_weight+green_weight<=100000,
|
|
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0ba690 |
the normalized graylevel is computed:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
int rw = red_weight * 65536;
|
|
Packit |
0ba690 |
int gw = green_weight * 65536;
|
|
Packit |
0ba690 |
int bw = 65536 - (rw + gw);
|
|
Packit |
0ba690 |
gray = (rw*red + gw*green + bw*blue)/65536;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The default values come from the PNG file cHRM chunk if present; otherwise, the
|
|
Packit |
0ba690 |
defaults correspond to the ITU-R recommendation 709, and also the sRGB color
|
|
Packit |
0ba690 |
space, as recommended in the Charles Poynton's Colour FAQ,
|
|
Packit |
0ba690 |
Copyright (c) 2006-11-28 Charles Poynton, in section 9:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
<http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
|
|
Packit |
0ba690 |
|
|
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0ba690 |
Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Libpng approximates this with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
which can be expressed with integers as
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Y = (6969 * R + 23434 * G + 2365 * B)/32768
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The calculation is done in a linear colorspace, if the image gamma
|
|
Packit |
0ba690 |
is known.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you have a grayscale and you are using png_set_expand_depth(),
|
|
Packit |
0ba690 |
png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
|
|
Packit |
0ba690 |
a higher bit-depth, you must either supply the background color as a gray
|
|
Packit |
0ba690 |
value at the original file bit-depth (need_expand = 1) or else supply the
|
|
Packit |
0ba690 |
background color as an RGB triplet at the final, expanded bit depth
|
|
Packit |
0ba690 |
(need_expand = 0). Similarly, if you are reading a paletted image, you
|
|
Packit |
0ba690 |
must either supply the background color as a palette index (need_expand = 1)
|
|
Packit |
0ba690 |
or as an RGB triplet that may or may not be in the palette (need_expand = 0).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_color_16 my_background;
|
|
Packit |
0ba690 |
png_color_16p image_background;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (png_get_bKGD(png_ptr, info_ptr, &image_background))
|
|
Packit |
0ba690 |
png_set_background(png_ptr, image_background,
|
|
Packit |
0ba690 |
PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
|
|
Packit |
0ba690 |
else
|
|
Packit |
0ba690 |
png_set_background(png_ptr, &my_background,
|
|
Packit |
0ba690 |
PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The png_set_background() function tells libpng to composite images
|
|
Packit |
0ba690 |
with alpha or simple transparency against the supplied background
|
|
Packit |
0ba690 |
color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
|
|
Packit |
0ba690 |
you may use this color, or supply another color more suitable for
|
|
Packit |
0ba690 |
the current display (e.g., the background color from a web page). You
|
|
Packit |
0ba690 |
need to tell libpng whether the color is in the gamma space of the
|
|
Packit |
0ba690 |
display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
|
|
Packit |
0ba690 |
(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
|
|
Packit |
0ba690 |
that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
|
|
Packit |
0ba690 |
know why anyone would use this, but it's here).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
To properly display PNG images on any kind of system, the application needs
|
|
Packit |
0ba690 |
to know what the display gamma is. Ideally, the user will know this, and
|
|
Packit |
0ba690 |
the application will allow them to set it. One method of allowing the user
|
|
Packit |
0ba690 |
to set the display gamma separately for each system is to check for a
|
|
Packit |
0ba690 |
SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
|
|
Packit |
0ba690 |
correctly set.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Note that display_gamma is the overall gamma correction required to produce
|
|
Packit |
0ba690 |
pleasing results, which depends on the lighting conditions in the surrounding
|
|
Packit |
0ba690 |
environment. In a dim or brightly lit room, no compensation other than
|
|
Packit |
0ba690 |
the physical gamma exponent of the monitor is needed, while in a dark room
|
|
Packit |
0ba690 |
a slightly smaller exponent is better.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
double gamma, screen_gamma;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (/* We have a user-defined screen
|
|
Packit |
0ba690 |
gamma value */)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
screen_gamma = user_defined_screen_gamma;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
/* One way that applications can share the same
|
|
Packit |
0ba690 |
screen gamma value */
|
|
Packit |
0ba690 |
else if ((gamma_str = getenv("SCREEN_GAMMA"))
|
|
Packit |
0ba690 |
!= NULL)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
screen_gamma = (double)atof(gamma_str);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
/* If we don't have another value */
|
|
Packit |
0ba690 |
else
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
screen_gamma = 2.2; /* A good guess for a
|
|
Packit |
0ba690 |
PC monitor in a bright office or a dim room */
|
|
Packit |
0ba690 |
screen_gamma = 2.0; /* A good guess for a
|
|
Packit |
0ba690 |
PC monitor in a dark room */
|
|
Packit |
0ba690 |
screen_gamma = 1.7 or 1.0; /* A good
|
|
Packit |
0ba690 |
guess for Mac systems */
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The png_set_gamma() function handles gamma transformations of the data.
|
|
Packit |
0ba690 |
Pass both the file gamma and the current screen_gamma. If the file does
|
|
Packit |
0ba690 |
not have a gamma value, you can pass one anyway if you have an idea what
|
|
Packit |
0ba690 |
it is (usually 0.45455 is a good guess for GIF images on PCs). Note
|
|
Packit |
0ba690 |
that file gammas are inverted from screen gammas. See the discussions
|
|
Packit |
0ba690 |
on gamma in the PNG specification for an excellent description of what
|
|
Packit |
0ba690 |
gamma is, and why all applications should support it. It is strongly
|
|
Packit |
0ba690 |
recommended that PNG viewers support gamma correction.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (png_get_gAMA(png_ptr, info_ptr, &gamma))
|
|
Packit |
0ba690 |
png_set_gamma(png_ptr, screen_gamma, gamma);
|
|
Packit |
0ba690 |
else
|
|
Packit |
0ba690 |
png_set_gamma(png_ptr, screen_gamma, 0.45455);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you need to reduce an RGB file to a paletted file, or if a paletted
|
|
Packit |
0ba690 |
file has more entries then will fit on your screen, png_set_dither()
|
|
Packit |
0ba690 |
will do that. Note that this is a simple match dither that merely
|
|
Packit |
0ba690 |
finds the closest color available. This should work fairly well with
|
|
Packit |
0ba690 |
optimized palettes, and fairly badly with linear color cubes. If you
|
|
Packit |
0ba690 |
pass a palette that is larger then maximum_colors, the file will
|
|
Packit |
0ba690 |
reduce the number of colors in the palette so it will fit into
|
|
Packit |
0ba690 |
maximum_colors. If there is a histogram, it will use it to make
|
|
Packit |
0ba690 |
more intelligent choices when reducing the palette. If there is no
|
|
Packit |
0ba690 |
histogram, it may not do as good a job.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type & PNG_COLOR_MASK_COLOR)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
if (png_get_valid(png_ptr, info_ptr,
|
|
Packit |
0ba690 |
PNG_INFO_PLTE))
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_uint_16p histogram = NULL;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_hIST(png_ptr, info_ptr,
|
|
Packit |
0ba690 |
&histogram);
|
|
Packit |
0ba690 |
png_set_dither(png_ptr, palette, num_palette,
|
|
Packit |
0ba690 |
max_screen_colors, histogram, 1);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
else
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_color std_color_cube[MAX_SCREEN_COLORS] =
|
|
Packit |
0ba690 |
{ ... colors ... };
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_dither(png_ptr, std_color_cube,
|
|
Packit |
0ba690 |
MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
|
|
Packit |
0ba690 |
NULL,0);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files describe monochrome as black being zero and white being one.
|
|
Packit |
0ba690 |
The following code will reverse this (make black be one and white be
|
|
Packit |
0ba690 |
zero):
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
|
|
Packit |
0ba690 |
png_set_invert_mono(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This function can also be used to invert grayscale and gray-alpha images:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|
Packit |
0ba690 |
color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|
Packit |
0ba690 |
png_set_invert_mono(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files store 16 bit pixels in network byte order (big-endian,
|
|
Packit |
0ba690 |
ie. most significant bits first). This code changes the storage to the
|
|
Packit |
0ba690 |
other way (little-endian, i.e. least significant bits first, the
|
|
Packit |
0ba690 |
way PCs store them):
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (bit_depth == 16)
|
|
Packit |
0ba690 |
png_set_swap(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|
Packit |
0ba690 |
need to change the order the pixels are packed into bytes, you can use:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (bit_depth < 8)
|
|
Packit |
0ba690 |
png_set_packswap(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Finally, you can write your own transformation function if none of
|
|
Packit |
0ba690 |
the existing ones meets your needs. This is done by setting a callback
|
|
Packit |
0ba690 |
with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_read_user_transform_fn(png_ptr,
|
|
Packit |
0ba690 |
read_transform_fn);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You must supply the function
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
void read_transform_fn(png_ptr ptr, row_info_ptr
|
|
Packit |
0ba690 |
row_info, png_bytep data)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
See pngtest.c for a working example. Your function will be called
|
|
Packit |
0ba690 |
after all of the other transformations have been processed.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You can also set up a pointer to a user structure for use by your
|
|
Packit |
0ba690 |
callback function, and you can inform libpng that your transform
|
|
Packit |
0ba690 |
function will change the number of channels or bit depth with the
|
|
Packit |
0ba690 |
function
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_user_transform_info(png_ptr, user_ptr,
|
|
Packit |
0ba690 |
user_depth, user_channels);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The user's application, not libpng, is responsible for allocating and
|
|
Packit |
0ba690 |
freeing any memory required for the user structure.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You can retrieve the pointer via the function
|
|
Packit |
0ba690 |
png_get_user_transform_ptr(). For example:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
voidp read_user_transform_ptr =
|
|
Packit |
0ba690 |
png_get_user_transform_ptr(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The last thing to handle is interlacing; this is covered in detail below,
|
|
Packit |
0ba690 |
but you must call the function here if you want libpng to handle expansion
|
|
Packit |
0ba690 |
of the interlaced image.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
number_of_passes = png_set_interlace_handling(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
After setting the transformations, libpng can update your png_info
|
|
Packit |
0ba690 |
structure to reflect any transformations you've requested with this
|
|
Packit |
0ba690 |
call. This is most useful to update the info structure's rowbytes
|
|
Packit |
0ba690 |
field so you can use it to allocate your image memory. This function
|
|
Packit |
0ba690 |
will also update your palette with the correct screen_gamma and
|
|
Packit |
0ba690 |
background if these have been given with the calls above.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_read_update_info(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
After you call png_read_update_info(), you can allocate any
|
|
Packit |
0ba690 |
memory you need to hold the image. The row data is simply
|
|
Packit |
0ba690 |
raw byte data for all forms of images. As the actual allocation
|
|
Packit |
0ba690 |
varies among applications, no example will be given. If you
|
|
Packit |
0ba690 |
are allocating one large chunk, you will need to build an
|
|
Packit |
0ba690 |
array of pointers to each row, as it will be needed for some
|
|
Packit |
0ba690 |
of the functions below.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Reading image data
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
After you've allocated memory, you can read the image data.
|
|
Packit |
0ba690 |
The simplest way to do this is in one function call. If you are
|
|
Packit |
0ba690 |
allocating enough memory to hold the whole image, you can just
|
|
Packit |
0ba690 |
call png_read_image() and libpng will read in all the image data
|
|
Packit |
0ba690 |
and put it in the memory area supplied. You will need to pass in
|
|
Packit |
0ba690 |
an array of pointers to each row.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This function automatically handles interlacing, so you don't need
|
|
Packit |
0ba690 |
to call png_set_interlace_handling() or call this function multiple
|
|
Packit |
0ba690 |
times, or any of that other stuff necessary with png_read_rows().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_read_image(png_ptr, row_pointers);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where row_pointers is:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_bytep row_pointers[height];
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You can point to void or char or whatever you use for pixels.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you don't want to read in the whole image at once, you can
|
|
Packit |
0ba690 |
use png_read_rows() instead. If there is no interlacing (check
|
|
Packit |
0ba690 |
interlace_type == PNG_INTERLACE_NONE), this is simple:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_read_rows(png_ptr, row_pointers, NULL,
|
|
Packit |
0ba690 |
number_of_rows);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where row_pointers is the same as in the png_read_image() call.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are doing this just one row at a time, you can do this with
|
|
Packit |
0ba690 |
a single row_pointer instead of an array of row_pointers:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_bytep row_pointer = row;
|
|
Packit |
0ba690 |
png_read_row(png_ptr, row_pointer, NULL);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
|
|
Packit |
0ba690 |
get somewhat harder. The only current (PNG Specification version 1.2)
|
|
Packit |
0ba690 |
interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
|
|
Packit |
0ba690 |
is a somewhat complicated 2D interlace scheme, known as Adam7, that
|
|
Packit |
0ba690 |
breaks down an image into seven smaller images of varying size, based
|
|
Packit |
0ba690 |
on an 8x8 grid.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
libpng can fill out those images or it can give them to you "as is".
|
|
Packit |
0ba690 |
If you want them filled out, there are two ways to do that. The one
|
|
Packit |
0ba690 |
mentioned in the PNG specification is to expand each pixel to cover
|
|
Packit |
0ba690 |
those pixels that have not been read yet (the "rectangle" method).
|
|
Packit |
0ba690 |
This results in a blocky image for the first pass, which gradually
|
|
Packit |
0ba690 |
smooths out as more pixels are read. The other method is the "sparkle"
|
|
Packit |
0ba690 |
method, where pixels are drawn only in their final locations, with the
|
|
Packit |
0ba690 |
rest of the image remaining whatever colors they were initialized to
|
|
Packit |
0ba690 |
before the start of the read. The first method usually looks better,
|
|
Packit |
0ba690 |
but tends to be slower, as there are more pixels to put in the rows.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you don't want libpng to handle the interlacing details, just call
|
|
Packit |
0ba690 |
png_read_rows() seven times to read in all seven images. Each of the
|
|
Packit |
0ba690 |
images is a valid image by itself, or they can all be combined on an
|
|
Packit |
0ba690 |
8x8 grid to form a single image (although if you intend to combine them
|
|
Packit |
0ba690 |
you would be far better off using the libpng interlace handling).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The first pass will return an image 1/8 as wide as the entire image
|
|
Packit |
0ba690 |
(every 8th column starting in column 0) and 1/8 as high as the original
|
|
Packit |
0ba690 |
(every 8th row starting in row 0), the second will be 1/8 as wide
|
|
Packit |
0ba690 |
(starting in column 4) and 1/8 as high (also starting in row 0). The
|
|
Packit |
0ba690 |
third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
|
|
Packit |
0ba690 |
1/8 as high (every 8th row starting in row 4), and the fourth pass will
|
|
Packit |
0ba690 |
be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
|
|
Packit |
0ba690 |
and every 4th row starting in row 0). The fifth pass will return an
|
|
Packit |
0ba690 |
image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
|
|
Packit |
0ba690 |
while the sixth pass will be 1/2 as wide and 1/2 as high as the original
|
|
Packit |
0ba690 |
(starting in column 1 and row 0). The seventh and final pass will be as
|
|
Packit |
0ba690 |
wide as the original, and 1/2 as high, containing all of the odd
|
|
Packit |
0ba690 |
numbered scanlines. Phew!
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you want libpng to expand the images, call this before calling
|
|
Packit |
0ba690 |
png_start_read_image() or png_read_update_info():
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (interlace_type == PNG_INTERLACE_ADAM7)
|
|
Packit |
0ba690 |
number_of_passes
|
|
Packit |
0ba690 |
= png_set_interlace_handling(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This will return the number of passes needed. Currently, this
|
|
Packit |
0ba690 |
is seven, but may change if another interlace type is added.
|
|
Packit |
0ba690 |
This function can be called even if the file is not interlaced,
|
|
Packit |
0ba690 |
where it will return one pass.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are not going to display the image after each pass, but are
|
|
Packit |
0ba690 |
going to wait until the entire image is read in, use the sparkle
|
|
Packit |
0ba690 |
effect. This effect is faster and the end result of either method
|
|
Packit |
0ba690 |
is exactly the same. If you are planning on displaying the image
|
|
Packit |
0ba690 |
after each pass, the "rectangle" effect is generally considered the
|
|
Packit |
0ba690 |
better looking one.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you only want the "sparkle" effect, just call png_read_rows() as
|
|
Packit |
0ba690 |
normal, with the third parameter NULL. Make sure you make pass over
|
|
Packit |
0ba690 |
the image number_of_passes times, and you don't change the data in the
|
|
Packit |
0ba690 |
rows between calls. You can change the locations of the data, just
|
|
Packit |
0ba690 |
not the data. Each pass only writes the pixels appropriate for that
|
|
Packit |
0ba690 |
pass, and assumes the data from previous passes is still valid.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_read_rows(png_ptr, row_pointers, NULL,
|
|
Packit |
0ba690 |
number_of_rows);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you only want the first effect (the rectangles), do the same as
|
|
Packit |
0ba690 |
before except pass the row buffer in the third parameter, and leave
|
|
Packit |
0ba690 |
the second parameter NULL.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_read_rows(png_ptr, NULL, row_pointers,
|
|
Packit |
0ba690 |
number_of_rows);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Finishing a sequential read
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
After you are finished reading the image through the
|
|
Packit |
0ba690 |
low-level interface, you can finish reading the file. If you are
|
|
Packit |
0ba690 |
interested in comments or time, which may be stored either before or
|
|
Packit |
0ba690 |
after the image data, you should pass the separate png_info struct if
|
|
Packit |
0ba690 |
you want to keep the comments from before and after the image
|
|
Packit |
0ba690 |
separate. If you are not interested, you can pass NULL.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_read_end(png_ptr, end_info);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
When you are done, you can free all memory allocated by libpng like this:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
Packit |
0ba690 |
&end_info);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
It is also possible to individually free the info_ptr members that
|
|
Packit |
0ba690 |
point to libpng-allocated storage with the following function:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_free_data(png_ptr, info_ptr, mask, seq)
|
|
Packit |
0ba690 |
mask - identifies data to be freed, a mask
|
|
Packit |
0ba690 |
containing the bitwise OR of one or
|
|
Packit |
0ba690 |
more of
|
|
Packit |
0ba690 |
PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|
Packit |
0ba690 |
PNG_FREE_HIST, PNG_FREE_ICCP,
|
|
Packit |
0ba690 |
PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|
Packit |
0ba690 |
PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|
Packit |
0ba690 |
PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|
Packit |
0ba690 |
or simply PNG_FREE_ALL
|
|
Packit |
0ba690 |
seq - sequence number of item to be freed
|
|
Packit |
0ba690 |
(\-1 for all items)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This function may be safely called when the relevant storage has
|
|
Packit |
0ba690 |
already been freed, or has not yet been allocated, or was allocated
|
|
Packit |
0ba690 |
by the user and not by libpng, and will in those cases do nothing.
|
|
Packit |
0ba690 |
The "seq" parameter is ignored if only one item of the selected data
|
|
Packit |
0ba690 |
type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
|
|
Packit |
0ba690 |
are allowed for the data type identified in the mask, such as text or
|
|
Packit |
0ba690 |
sPLT, only the n'th item in the structure is freed, where n is "seq".
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The default behavior is only to free data that was allocated internally
|
|
Packit |
0ba690 |
by libpng. This can be changed, so that libpng will not free the data,
|
|
Packit |
0ba690 |
or so that it will free data that was allocated by the user with png_malloc()
|
|
Packit |
0ba690 |
or png_zalloc() and passed in via a png_set_*() function, with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_data_freer(png_ptr, info_ptr, freer, mask)
|
|
Packit |
0ba690 |
mask - which data elements are affected
|
|
Packit |
0ba690 |
same choices as in png_free_data()
|
|
Packit |
0ba690 |
freer - one of
|
|
Packit |
0ba690 |
PNG_DESTROY_WILL_FREE_DATA
|
|
Packit |
0ba690 |
PNG_SET_WILL_FREE_DATA
|
|
Packit |
0ba690 |
PNG_USER_WILL_FREE_DATA
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This function only affects data that has already been allocated.
|
|
Packit |
0ba690 |
You can call this function after reading the PNG data but before calling
|
|
Packit |
0ba690 |
any png_set_*() functions, to control whether the user or the png_set_*()
|
|
Packit |
0ba690 |
function is responsible for freeing any existing data that might be present,
|
|
Packit |
0ba690 |
and again after the png_set_*() functions to control whether the user
|
|
Packit |
0ba690 |
or png_destroy_*() is supposed to free the data. When the user assumes
|
|
Packit |
0ba690 |
responsibility for libpng-allocated data, the application must use
|
|
Packit |
0ba690 |
png_free() to free it, and when the user transfers responsibility to libpng
|
|
Packit |
0ba690 |
for data that the user has allocated, the user must have used png_malloc()
|
|
Packit |
0ba690 |
or png_zalloc() to allocate it.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you allocated your row_pointers in a single block, as suggested above in
|
|
Packit |
0ba690 |
the description of the high level read interface, you must not transfer
|
|
Packit |
0ba690 |
responsibility for freeing it to the png_set_rows or png_read_destroy function,
|
|
Packit |
0ba690 |
because they would also try to free the individual row_pointers[i].
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|
Packit |
0ba690 |
separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|
Packit |
0ba690 |
because when libpng fills a png_text structure it combines these members with
|
|
Packit |
0ba690 |
the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|
Packit |
0ba690 |
if you transfer responsibility for free'ing text_ptr from libpng to your
|
|
Packit |
0ba690 |
application, your application must not separately free those members.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The png_free_data() function will turn off the "valid" flag for anything
|
|
Packit |
0ba690 |
it frees. If you need to turn the flag off for a chunk that was freed by
|
|
Packit |
0ba690 |
your application instead of by libpng, you can use
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_invalid(png_ptr, info_ptr, mask);
|
|
Packit |
0ba690 |
mask - identifies the chunks to be made invalid,
|
|
Packit |
0ba690 |
containing the bitwise OR of one or
|
|
Packit |
0ba690 |
more of
|
|
Packit |
0ba690 |
PNG_INFO_gAMA, PNG_INFO_sBIT,
|
|
Packit |
0ba690 |
PNG_INFO_cHRM, PNG_INFO_PLTE,
|
|
Packit |
0ba690 |
PNG_INFO_tRNS, PNG_INFO_bKGD,
|
|
Packit |
0ba690 |
PNG_INFO_hIST, PNG_INFO_pHYs,
|
|
Packit |
0ba690 |
PNG_INFO_oFFs, PNG_INFO_tIME,
|
|
Packit |
0ba690 |
PNG_INFO_pCAL, PNG_INFO_sRGB,
|
|
Packit |
0ba690 |
PNG_INFO_iCCP, PNG_INFO_sPLT,
|
|
Packit |
0ba690 |
PNG_INFO_sCAL, PNG_INFO_IDAT
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
For a more compact example of reading a PNG image, see the file example.c.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Reading PNG files progressively
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The progressive reader is slightly different then the non-progressive
|
|
Packit |
0ba690 |
reader. Instead of calling png_read_info(), png_read_rows(), and
|
|
Packit |
0ba690 |
png_read_end(), you make one call to png_process_data(), which calls
|
|
Packit |
0ba690 |
callbacks when it has the info, a row, or the end of the image. You
|
|
Packit |
0ba690 |
set up these callbacks with png_set_progressive_read_fn(). You don't
|
|
Packit |
0ba690 |
have to worry about the input/output functions of libpng, as you are
|
|
Packit |
0ba690 |
giving the library the data directly in png_process_data(). I will
|
|
Packit |
0ba690 |
assume that you have read the section on reading PNG files above,
|
|
Packit |
0ba690 |
so I will only highlight the differences (although I will show
|
|
Packit |
0ba690 |
all of the code).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_structp png_ptr;
|
|
Packit |
0ba690 |
png_infop info_ptr;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* An example code fragment of how you would
|
|
Packit |
0ba690 |
initialize the progressive reader in your
|
|
Packit |
0ba690 |
application. */
|
|
Packit |
0ba690 |
int
|
|
Packit |
0ba690 |
initialize_png_reader()
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_ptr = png_create_read_struct
|
|
Packit |
0ba690 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
Packit |
0ba690 |
user_error_fn, user_warning_fn);
|
|
Packit |
0ba690 |
if (!png_ptr)
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
info_ptr = png_create_info_struct(png_ptr);
|
|
Packit |
0ba690 |
if (!info_ptr)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
|
|
Packit |
0ba690 |
(png_infopp)NULL);
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (setjmp(png_jmpbuf(png_ptr)))
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
Packit |
0ba690 |
(png_infopp)NULL);
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* This one's new. You can provide functions
|
|
Packit |
0ba690 |
to be called when the header info is valid,
|
|
Packit |
0ba690 |
when each row is completed, and when the image
|
|
Packit |
0ba690 |
is finished. If you aren't using all functions,
|
|
Packit |
0ba690 |
you can specify NULL parameters. Even when all
|
|
Packit |
0ba690 |
three functions are NULL, you need to call
|
|
Packit |
0ba690 |
png_set_progressive_read_fn(). You can use
|
|
Packit |
0ba690 |
any struct as the user_ptr (cast to a void pointer
|
|
Packit |
0ba690 |
for the function call), and retrieve the pointer
|
|
Packit |
0ba690 |
from inside the callbacks using the function
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_get_progressive_ptr(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
which will return a void pointer, which you have
|
|
Packit |
0ba690 |
to cast appropriately.
|
|
Packit |
0ba690 |
*/
|
|
Packit |
0ba690 |
png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
|
|
Packit |
0ba690 |
info_callback, row_callback, end_callback);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
return 0;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* A code fragment that you call as you receive blocks
|
|
Packit |
0ba690 |
of data */
|
|
Packit |
0ba690 |
int
|
|
Packit |
0ba690 |
process_data(png_bytep buffer, png_uint_32 length)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
if (setjmp(png_jmpbuf(png_ptr)))
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
Packit |
0ba690 |
(png_infopp)NULL);
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* This one's new also. Simply give it a chunk
|
|
Packit |
0ba690 |
of data from the file stream (in order, of
|
|
Packit |
0ba690 |
course). On machines with segmented memory
|
|
Packit |
0ba690 |
models machines, don't give it any more than
|
|
Packit |
0ba690 |
64K. The library seems to run fine with sizes
|
|
Packit |
0ba690 |
of 4K. Although you can give it much less if
|
|
Packit |
0ba690 |
necessary (I assume you can give it chunks of
|
|
Packit |
0ba690 |
1 byte, I haven't tried less then 256 bytes
|
|
Packit |
0ba690 |
yet). When this function returns, you may
|
|
Packit |
0ba690 |
want to display any rows that were generated
|
|
Packit |
0ba690 |
in the row callback if you don't already do
|
|
Packit |
0ba690 |
so there.
|
|
Packit |
0ba690 |
*/
|
|
Packit |
0ba690 |
png_process_data(png_ptr, info_ptr, buffer, length);
|
|
Packit |
0ba690 |
return 0;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* This function is called (as set by
|
|
Packit |
0ba690 |
png_set_progressive_read_fn() above) when enough data
|
|
Packit |
0ba690 |
has been supplied so all of the header has been
|
|
Packit |
0ba690 |
read.
|
|
Packit |
0ba690 |
*/
|
|
Packit |
0ba690 |
void
|
|
Packit |
0ba690 |
info_callback(png_structp png_ptr, png_infop info)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
/* Do any setup here, including setting any of
|
|
Packit |
0ba690 |
the transformations mentioned in the Reading
|
|
Packit |
0ba690 |
PNG files section. For now, you _must_ call
|
|
Packit |
0ba690 |
either png_start_read_image() or
|
|
Packit |
0ba690 |
png_read_update_info() after all the
|
|
Packit |
0ba690 |
transformations are set (even if you don't set
|
|
Packit |
0ba690 |
any). You may start getting rows before
|
|
Packit |
0ba690 |
png_process_data() returns, so this is your
|
|
Packit |
0ba690 |
last chance to prepare for that.
|
|
Packit |
0ba690 |
*/
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* This function is called when each row of image
|
|
Packit |
0ba690 |
data is complete */
|
|
Packit |
0ba690 |
void
|
|
Packit |
0ba690 |
row_callback(png_structp png_ptr, png_bytep new_row,
|
|
Packit |
0ba690 |
png_uint_32 row_num, int pass)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
/* If the image is interlaced, and you turned
|
|
Packit |
0ba690 |
on the interlace handler, this function will
|
|
Packit |
0ba690 |
be called for every row in every pass. Some
|
|
Packit |
0ba690 |
of these rows will not be changed from the
|
|
Packit |
0ba690 |
previous pass. When the row is not changed,
|
|
Packit |
0ba690 |
the new_row variable will be NULL. The rows
|
|
Packit |
0ba690 |
and passes are called in order, so you don't
|
|
Packit |
0ba690 |
really need the row_num and pass, but I'm
|
|
Packit |
0ba690 |
supplying them because it may make your life
|
|
Packit |
0ba690 |
easier.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
For the non-NULL rows of interlaced images,
|
|
Packit |
0ba690 |
you must call png_progressive_combine_row()
|
|
Packit |
0ba690 |
passing in the row and the old row. You can
|
|
Packit |
0ba690 |
call this function for NULL rows (it will just
|
|
Packit |
0ba690 |
return) and for non-interlaced images (it just
|
|
Packit |
0ba690 |
does the memcpy for you) if it will make the
|
|
Packit |
0ba690 |
code easier. Thus, you can just do this for
|
|
Packit |
0ba690 |
all cases:
|
|
Packit |
0ba690 |
*/
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_progressive_combine_row(png_ptr, old_row,
|
|
Packit |
0ba690 |
new_row);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* where old_row is what was displayed for
|
|
Packit |
0ba690 |
previously for the row. Note that the first
|
|
Packit |
0ba690 |
pass (pass == 0, really) will completely cover
|
|
Packit |
0ba690 |
the old row, so the rows do not have to be
|
|
Packit |
0ba690 |
initialized. After the first pass (and only
|
|
Packit |
0ba690 |
for interlaced images), you will have to pass
|
|
Packit |
0ba690 |
the current row, and the function will combine
|
|
Packit |
0ba690 |
the old row and the new row.
|
|
Packit |
0ba690 |
*/
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
void
|
|
Packit |
0ba690 |
end_callback(png_structp png_ptr, png_infop info)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
/* This function is called after the whole image
|
|
Packit |
0ba690 |
has been read, including any chunks after the
|
|
Packit |
0ba690 |
image (up to and including the IEND). You
|
|
Packit |
0ba690 |
will usually have the same info chunk as you
|
|
Packit |
0ba690 |
had in the header, although some data may have
|
|
Packit |
0ba690 |
been added to the comments and time fields.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Most people won't do much here, perhaps setting
|
|
Packit |
0ba690 |
a flag that marks the image as finished.
|
|
Packit |
0ba690 |
*/
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH IV. Writing
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Much of this is very similar to reading. However, everything of
|
|
Packit |
0ba690 |
importance is repeated here, so you won't have to constantly look
|
|
Packit |
0ba690 |
back up in the reading section to understand writing.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Setup
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You will want to do the I/O initialization before you get into libpng,
|
|
Packit |
0ba690 |
so if it doesn't work, you don't have anything to undo. If you are not
|
|
Packit |
0ba690 |
using the standard I/O functions, you will need to replace them with
|
|
Packit |
0ba690 |
custom writing functions. See the discussion under Customizing libpng.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
FILE *fp = fopen(file_name, "wb");
|
|
Packit |
0ba690 |
if (!fp)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Next, png_struct and png_info need to be allocated and initialized.
|
|
Packit |
0ba690 |
As these can be both relatively large, you may not want to store these
|
|
Packit |
0ba690 |
on the stack, unless you have stack space to spare. Of course, you
|
|
Packit |
0ba690 |
will want to check if they return NULL. If you are also reading,
|
|
Packit |
0ba690 |
you won't want to name your read structure and your write structure
|
|
Packit |
0ba690 |
both "png_ptr"; you can call them anything you like, such as
|
|
Packit |
0ba690 |
"read_ptr" and "write_ptr". Look at pngtest.c, for example.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_structp png_ptr = png_create_write_struct
|
|
Packit |
0ba690 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
Packit |
0ba690 |
user_error_fn, user_warning_fn);
|
|
Packit |
0ba690 |
if (!png_ptr)
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_infop info_ptr = png_create_info_struct(png_ptr);
|
|
Packit |
0ba690 |
if (!info_ptr)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_destroy_write_struct(&png_ptr,
|
|
Packit |
0ba690 |
(png_infopp)NULL);
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you want to use your own memory allocation routines,
|
|
Packit |
0ba690 |
define PNG_USER_MEM_SUPPORTED and use
|
|
Packit |
0ba690 |
png_create_write_struct_2() instead of png_create_write_struct():
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_structp png_ptr = png_create_write_struct_2
|
|
Packit |
0ba690 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
Packit |
0ba690 |
user_error_fn, user_warning_fn, (png_voidp)
|
|
Packit |
0ba690 |
user_mem_ptr, user_malloc_fn, user_free_fn);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
After you have these structures, you will need to set up the
|
|
Packit |
0ba690 |
error handling. When libpng encounters an error, it expects to
|
|
Packit |
0ba690 |
longjmp() back to your routine. Therefore, you will need to call
|
|
Packit |
0ba690 |
setjmp() and pass the png_jmpbuf(png_ptr). If you
|
|
Packit |
0ba690 |
write the file from different routines, you will need to update
|
|
Packit |
0ba690 |
the png_jmpbuf(png_ptr) every time you enter a new routine that will
|
|
Packit |
0ba690 |
call a png_*() function. See your documentation of setjmp/longjmp
|
|
Packit |
0ba690 |
for your compiler for more information on setjmp/longjmp. See
|
|
Packit |
0ba690 |
the discussion on libpng error handling in the Customizing Libpng
|
|
Packit |
0ba690 |
section below for more information on the libpng error handling.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (setjmp(png_jmpbuf(png_ptr)))
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
png_destroy_write_struct(&png_ptr, &info_ptr);
|
|
Packit |
0ba690 |
fclose(fp);
|
|
Packit |
0ba690 |
return (ERROR);
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
...
|
|
Packit |
0ba690 |
return;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you would rather avoid the complexity of setjmp/longjmp issues,
|
|
Packit |
0ba690 |
you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
|
|
Packit |
0ba690 |
errors will result in a call to PNG_ABORT() which defaults to abort().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Now you need to set up the output code. The default for libpng is to
|
|
Packit |
0ba690 |
use the C function fwrite(). If you use this, you will need to pass a
|
|
Packit |
0ba690 |
valid FILE * in the function png_init_io(). Be sure that the file is
|
|
Packit |
0ba690 |
opened in binary mode. Again, if you wish to handle writing data in
|
|
Packit |
0ba690 |
another way, see the discussion on libpng I/O handling in the Customizing
|
|
Packit |
0ba690 |
Libpng section below.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_init_io(png_ptr, fp);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are embedding your PNG into a datastream such as MNG, and don't
|
|
Packit |
0ba690 |
want libpng to write the 8-byte signature, or if you have already
|
|
Packit |
0ba690 |
written the signature in your application, use
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_sig_bytes(png_ptr, 8);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
to inform libpng that it should not write a signature.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Write callbacks
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
At this point, you can set up a callback function that will be
|
|
Packit |
0ba690 |
called after each row has been written, which you can use to control
|
|
Packit |
0ba690 |
a progress meter or the like. It's demonstrated in pngtest.c.
|
|
Packit |
0ba690 |
You must supply a function
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
void write_row_callback(png_ptr, png_uint_32 row,
|
|
Packit |
0ba690 |
int pass);
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
/* put your code here */
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
(You can give it another name that you like instead of "write_row_callback")
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
To inform libpng about your function, use
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_write_status_fn(png_ptr, write_row_callback);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You now have the option of modifying how the compression library will
|
|
Packit |
0ba690 |
run. The following functions are mainly for testing, but may be useful
|
|
Packit |
0ba690 |
in some cases, like if you need to write PNG files extremely fast and
|
|
Packit |
0ba690 |
are willing to give up some compression, or if you want to get the
|
|
Packit |
0ba690 |
maximum possible compression at the expense of slower writing. If you
|
|
Packit |
0ba690 |
have no special needs in this area, let the library do what it wants by
|
|
Packit |
0ba690 |
not calling this function at all, as it has been tuned to deliver a good
|
|
Packit |
0ba690 |
speed/compression ratio. The second parameter to png_set_filter() is
|
|
Packit |
0ba690 |
the filter method, for which the only valid values are 0 (as of the
|
|
Packit |
0ba690 |
July 1999 PNG specification, version 1.2) or 64 (if you are writing
|
|
Packit |
0ba690 |
a PNG datastream that is to be embedded in a MNG datastream). The third
|
|
Packit |
0ba690 |
parameter is a flag that indicates which filter type(s) are to be tested
|
|
Packit |
0ba690 |
for each scanline. See the PNG specification for details on the specific
|
|
Packit |
0ba690 |
filter types.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* turn on or off filtering, and/or choose
|
|
Packit |
0ba690 |
specific filters. You can use either a single
|
|
Packit |
0ba690 |
PNG_FILTER_VALUE_NAME or the bitwise OR of one
|
|
Packit |
0ba690 |
or more PNG_FILTER_NAME masks. */
|
|
Packit |
0ba690 |
png_set_filter(png_ptr, 0,
|
|
Packit |
0ba690 |
PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
|
|
Packit |
0ba690 |
PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
|
|
Packit |
0ba690 |
PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
|
|
Packit |
0ba690 |
PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
|
|
Packit |
0ba690 |
PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
|
|
Packit |
0ba690 |
PNG_ALL_FILTERS);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If an application
|
|
Packit |
0ba690 |
wants to start and stop using particular filters during compression,
|
|
Packit |
0ba690 |
it should start out with all of the filters (to ensure that the previous
|
|
Packit |
0ba690 |
row of pixels will be stored in case it's needed later), and then add
|
|
Packit |
0ba690 |
and remove them after the start of compression.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are writing a PNG datastream that is to be embedded in a MNG
|
|
Packit |
0ba690 |
datastream, the second parameter can be either 0 or 64.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The png_set_compression_*() functions interface to the zlib compression
|
|
Packit |
0ba690 |
library, and should mostly be ignored unless you really know what you are
|
|
Packit |
0ba690 |
doing. The only generally useful call is png_set_compression_level()
|
|
Packit |
0ba690 |
which changes how much time zlib spends on trying to compress the image
|
|
Packit |
0ba690 |
data. See the Compression Library (zlib.h and algorithm.txt, distributed
|
|
Packit |
0ba690 |
with zlib) for details on the compression levels.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* set the zlib compression level */
|
|
Packit |
0ba690 |
png_set_compression_level(png_ptr,
|
|
Packit |
0ba690 |
Z_BEST_COMPRESSION);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* set other zlib parameters */
|
|
Packit |
0ba690 |
png_set_compression_mem_level(png_ptr, 8);
|
|
Packit |
0ba690 |
png_set_compression_strategy(png_ptr,
|
|
Packit |
0ba690 |
Z_DEFAULT_STRATEGY);
|
|
Packit |
0ba690 |
png_set_compression_window_bits(png_ptr, 15);
|
|
Packit |
0ba690 |
png_set_compression_method(png_ptr, 8);
|
|
Packit |
0ba690 |
png_set_compression_buffer_size(png_ptr, 8192)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
extern PNG_EXPORT(void,png_set_zbuf_size)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Setting the contents of info for output
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You now need to fill in the png_info structure with all the data you
|
|
Packit |
0ba690 |
wish to write before the actual image. Note that the only thing you
|
|
Packit |
0ba690 |
are allowed to write after the image is the text chunks and the time
|
|
Packit |
0ba690 |
chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
|
|
Packit |
0ba690 |
the latest PNG specification for more information on that. If you
|
|
Packit |
0ba690 |
wish to write them before the image, fill them in now, and flag that
|
|
Packit |
0ba690 |
data as being valid. If you want to wait until after the data, don't
|
|
Packit |
0ba690 |
fill them until png_write_end(). For all the fields in png_info and
|
|
Packit |
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their data types, see png.h. For explanations of what the fields
|
|
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contain, see the PNG specification.
|
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Some of the more important parts of the png_info are:
|
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|
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png_set_IHDR(png_ptr, info_ptr, width, height,
|
|
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bit_depth, color_type, interlace_type,
|
|
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compression_type, filter_method)
|
|
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width - holds the width of the image
|
|
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in pixels (up to 2^31).
|
|
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height - holds the height of the image
|
|
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in pixels (up to 2^31).
|
|
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bit_depth - holds the bit depth of one of the
|
|
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image channels.
|
|
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(valid values are 1, 2, 4, 8, 16
|
|
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and depend also on the
|
|
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color_type. See also significant
|
|
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bits (sBIT) below).
|
|
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color_type - describes which color/alpha
|
|
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channels are present.
|
|
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PNG_COLOR_TYPE_GRAY
|
|
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(bit depths 1, 2, 4, 8, 16)
|
|
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PNG_COLOR_TYPE_GRAY_ALPHA
|
|
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(bit depths 8, 16)
|
|
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PNG_COLOR_TYPE_PALETTE
|
|
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(bit depths 1, 2, 4, 8)
|
|
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PNG_COLOR_TYPE_RGB
|
|
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(bit_depths 8, 16)
|
|
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PNG_COLOR_TYPE_RGB_ALPHA
|
|
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(bit_depths 8, 16)
|
|
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|
|
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PNG_COLOR_MASK_PALETTE
|
|
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PNG_COLOR_MASK_COLOR
|
|
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PNG_COLOR_MASK_ALPHA
|
|
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|
|
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interlace_type - PNG_INTERLACE_NONE or
|
|
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PNG_INTERLACE_ADAM7
|
|
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compression_type - (must be
|
|
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PNG_COMPRESSION_TYPE_DEFAULT)
|
|
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filter_method - (must be PNG_FILTER_TYPE_DEFAULT
|
|
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or, if you are writing a PNG to
|
|
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be embedded in a MNG datastream,
|
|
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can also be
|
|
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PNG_INTRAPIXEL_DIFFERENCING)
|
|
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|
|
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If you call png_set_IHDR(), the call must appear before any of the
|
|
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other png_set_*() functions, because they might require access to some of
|
|
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the IHDR settings. The remaining png_set_*() functions can be called
|
|
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in any order.
|
|
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|
|
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If you wish, you can reset the compression_type, interlace_type, or
|
|
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filter_method later by calling png_set_IHDR() again; if you do this, the
|
|
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width, height, bit_depth, and color_type must be the same in each call.
|
|
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|
|
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png_set_PLTE(png_ptr, info_ptr, palette,
|
|
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num_palette);
|
|
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palette - the palette for the file
|
|
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(array of png_color)
|
|
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num_palette - number of entries in the palette
|
|
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|
|
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|
|
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png_set_gAMA(png_ptr, info_ptr, gamma);
|
|
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gamma - the gamma the image was created
|
|
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at (PNG_INFO_gAMA)
|
|
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|
|
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png_set_sRGB(png_ptr, info_ptr, srgb_intent);
|
|
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srgb_intent - the rendering intent
|
|
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(PNG_INFO_sRGB) The presence of
|
|
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the sRGB chunk means that the pixel
|
|
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data is in the sRGB color space.
|
|
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This chunk also implies specific
|
|
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values of gAMA and cHRM. Rendering
|
|
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intent is the CSS-1 property that
|
|
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has been defined by the International
|
|
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Color Consortium
|
|
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(http://www.color.org).
|
|
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It can be one of
|
|
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PNG_sRGB_INTENT_SATURATION,
|
|
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PNG_sRGB_INTENT_PERCEPTUAL,
|
|
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PNG_sRGB_INTENT_ABSOLUTE, or
|
|
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PNG_sRGB_INTENT_RELATIVE.
|
|
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|
|
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|
|
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png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
|
|
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srgb_intent);
|
|
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srgb_intent - the rendering intent
|
|
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(PNG_INFO_sRGB) The presence of the
|
|
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sRGB chunk means that the pixel
|
|
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data is in the sRGB color space.
|
|
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This function also causes gAMA and
|
|
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cHRM chunks with the specific values
|
|
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that are consistent with sRGB to be
|
|
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written.
|
|
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|
|
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png_set_iCCP(png_ptr, info_ptr, name, compression_type,
|
|
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profile, proflen);
|
|
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name - The profile name.
|
|
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compression - The compression type; always
|
|
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PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|
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You may give NULL to this argument to
|
|
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ignore it.
|
|
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profile - International Color Consortium color
|
|
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profile data. May contain NULs.
|
|
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proflen - length of profile data in bytes.
|
|
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|
|
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png_set_sBIT(png_ptr, info_ptr, sig_bit);
|
|
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sig_bit - the number of significant bits for
|
|
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(PNG_INFO_sBIT) each of the gray, red,
|
|
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green, and blue channels, whichever are
|
|
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appropriate for the given color type
|
|
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(png_color_16)
|
|
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0ba690 |
|
|
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png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
|
|
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trans_values);
|
|
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trans - array of transparent
|
|
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entries for palette (PNG_INFO_tRNS)
|
|
Packit |
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trans_values - graylevel or color sample values
|
|
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(in order red, green, blue) of the
|
|
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single transparent color for
|
|
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non-paletted images (PNG_INFO_tRNS)
|
|
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num_trans - number of transparent entries
|
|
Packit |
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(PNG_INFO_tRNS)
|
|
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|
|
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png_set_hIST(png_ptr, info_ptr, hist);
|
|
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(PNG_INFO_hIST)
|
|
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hist - histogram of palette (array of
|
|
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png_uint_16)
|
|
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|
|
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png_set_tIME(png_ptr, info_ptr, mod_time);
|
|
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mod_time - time image was last modified
|
|
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(PNG_VALID_tIME)
|
|
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0ba690 |
|
|
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png_set_bKGD(png_ptr, info_ptr, background);
|
|
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background - background color (PNG_VALID_bKGD)
|
|
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0ba690 |
|
|
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png_set_text(png_ptr, info_ptr, text_ptr, num_text);
|
|
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text_ptr - array of png_text holding image
|
|
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comments
|
|
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text_ptr[i].compression - type of compression used
|
|
Packit |
0ba690 |
on "text" PNG_TEXT_COMPRESSION_NONE
|
|
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PNG_TEXT_COMPRESSION_zTXt
|
|
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PNG_ITXT_COMPRESSION_NONE
|
|
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PNG_ITXT_COMPRESSION_zTXt
|
|
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text_ptr[i].key - keyword for comment. Must contain
|
|
Packit |
0ba690 |
1-79 characters.
|
|
Packit |
0ba690 |
text_ptr[i].text - text comments for current
|
|
Packit |
0ba690 |
keyword. Can be NULL or empty.
|
|
Packit |
0ba690 |
text_ptr[i].text_length - length of text string,
|
|
Packit |
0ba690 |
after decompression, 0 for iTXt
|
|
Packit |
0ba690 |
text_ptr[i].itxt_length - length of itxt string,
|
|
Packit |
0ba690 |
after decompression, 0 for tEXt/zTXt
|
|
Packit |
0ba690 |
text_ptr[i].lang - language of comment (NULL or
|
|
Packit |
0ba690 |
empty for unknown).
|
|
Packit |
0ba690 |
text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
|
|
Packit |
0ba690 |
or empty for unknown).
|
|
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0ba690 |
Note that the itxt_length, lang, and lang_key
|
|
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0ba690 |
members of the text_ptr structure only exist
|
|
Packit |
0ba690 |
when the library is built with iTXt chunk support.
|
|
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0ba690 |
|
|
Packit |
0ba690 |
num_text - number of comments
|
|
Packit |
0ba690 |
|
|
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png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
|
|
Packit |
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num_spalettes);
|
|
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0ba690 |
palette_ptr - array of png_sPLT_struct structures
|
|
Packit |
0ba690 |
to be added to the list of palettes
|
|
Packit |
0ba690 |
in the info structure.
|
|
Packit |
0ba690 |
num_spalettes - number of palette structures to be
|
|
Packit |
0ba690 |
added.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
|
|
Packit |
0ba690 |
unit_type);
|
|
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0ba690 |
offset_x - positive offset from the left
|
|
Packit |
0ba690 |
edge of the screen
|
|
Packit |
0ba690 |
offset_y - positive offset from the top
|
|
Packit |
0ba690 |
edge of the screen
|
|
Packit |
0ba690 |
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|
Packit |
0ba690 |
|
|
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0ba690 |
png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
|
|
Packit |
0ba690 |
unit_type);
|
|
Packit |
0ba690 |
res_x - pixels/unit physical resolution
|
|
Packit |
0ba690 |
in x direction
|
|
Packit |
0ba690 |
res_y - pixels/unit physical resolution
|
|
Packit |
0ba690 |
in y direction
|
|
Packit |
0ba690 |
unit_type - PNG_RESOLUTION_UNKNOWN,
|
|
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0ba690 |
PNG_RESOLUTION_METER
|
|
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0ba690 |
|
|
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0ba690 |
png_set_sCAL(png_ptr, info_ptr, unit, width, height)
|
|
Packit |
0ba690 |
unit - physical scale units (an integer)
|
|
Packit |
0ba690 |
width - width of a pixel in physical scale units
|
|
Packit |
0ba690 |
height - height of a pixel in physical scale units
|
|
Packit |
0ba690 |
(width and height are doubles)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
|
|
Packit |
0ba690 |
unit - physical scale units (an integer)
|
|
Packit |
0ba690 |
width - width of a pixel in physical scale units
|
|
Packit |
0ba690 |
height - height of a pixel in physical scale units
|
|
Packit |
0ba690 |
(width and height are strings like "2.54")
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
|
|
Packit |
0ba690 |
num_unknowns)
|
|
Packit |
0ba690 |
unknowns - array of png_unknown_chunk
|
|
Packit |
0ba690 |
structures holding unknown chunks
|
|
Packit |
0ba690 |
unknowns[i].name - name of unknown chunk
|
|
Packit |
0ba690 |
unknowns[i].data - data of unknown chunk
|
|
Packit |
0ba690 |
unknowns[i].size - size of unknown chunk's data
|
|
Packit |
0ba690 |
unknowns[i].location - position to write chunk in file
|
|
Packit |
0ba690 |
0: do not write chunk
|
|
Packit |
0ba690 |
PNG_HAVE_IHDR: before PLTE
|
|
Packit |
0ba690 |
PNG_HAVE_PLTE: before IDAT
|
|
Packit |
0ba690 |
PNG_AFTER_IDAT: after IDAT
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The "location" member is set automatically according to
|
|
Packit |
0ba690 |
what part of the output file has already been written.
|
|
Packit |
0ba690 |
You can change its value after calling png_set_unknown_chunks()
|
|
Packit |
0ba690 |
as demonstrated in pngtest.c. Within each of the "locations",
|
|
Packit |
0ba690 |
the chunks are sequenced according to their position in the
|
|
Packit |
0ba690 |
structure (that is, the value of "i", which is the order in which
|
|
Packit |
0ba690 |
the chunk was either read from the input file or defined with
|
|
Packit |
0ba690 |
png_set_unknown_chunks).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
A quick word about text and num_text. text is an array of png_text
|
|
Packit |
0ba690 |
structures. num_text is the number of valid structures in the array.
|
|
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0ba690 |
Each png_text structure holds a language code, a keyword, a text value,
|
|
Packit |
0ba690 |
and a compression type.
|
|
Packit |
0ba690 |
|
|
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0ba690 |
The compression types have the same valid numbers as the compression
|
|
Packit |
0ba690 |
types of the image data. Currently, the only valid number is zero.
|
|
Packit |
0ba690 |
However, you can store text either compressed or uncompressed, unlike
|
|
Packit |
0ba690 |
images, which always have to be compressed. So if you don't want the
|
|
Packit |
0ba690 |
text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
|
|
Packit |
0ba690 |
Because tEXt and zTXt chunks don't have a language field, if you
|
|
Packit |
0ba690 |
specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
|
|
Packit |
0ba690 |
any language code or translated keyword will not be written out.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Until text gets around 1000 bytes, it is not worth compressing it.
|
|
Packit |
0ba690 |
After the text has been written out to the file, the compression type
|
|
Packit |
0ba690 |
is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
|
|
Packit |
0ba690 |
so that it isn't written out again at the end (in case you are calling
|
|
Packit |
0ba690 |
png_write_end() with the same struct.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The keywords that are given in the PNG Specification are:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Title Short (one line) title or
|
|
Packit |
0ba690 |
caption for image
|
|
Packit |
0ba690 |
Author Name of image's creator
|
|
Packit |
0ba690 |
Description Description of image (possibly long)
|
|
Packit |
0ba690 |
Copyright Copyright notice
|
|
Packit |
0ba690 |
Creation Time Time of original image creation
|
|
Packit |
0ba690 |
(usually RFC 1123 format, see below)
|
|
Packit |
0ba690 |
Software Software used to create the image
|
|
Packit |
0ba690 |
Disclaimer Legal disclaimer
|
|
Packit |
0ba690 |
Warning Warning of nature of content
|
|
Packit |
0ba690 |
Source Device used to create the image
|
|
Packit |
0ba690 |
Comment Miscellaneous comment; conversion
|
|
Packit |
0ba690 |
from other image format
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The keyword-text pairs work like this. Keywords should be short
|
|
Packit |
0ba690 |
simple descriptions of what the comment is about. Some typical
|
|
Packit |
0ba690 |
keywords are found in the PNG specification, as is some recommendations
|
|
Packit |
0ba690 |
on keywords. You can repeat keywords in a file. You can even write
|
|
Packit |
0ba690 |
some text before the image and some after. For example, you may want
|
|
Packit |
0ba690 |
to put a description of the image before the image, but leave the
|
|
Packit |
0ba690 |
disclaimer until after, so viewers working over modem connections
|
|
Packit |
0ba690 |
don't have to wait for the disclaimer to go over the modem before
|
|
Packit |
0ba690 |
they start seeing the image. Finally, keywords should be full
|
|
Packit |
0ba690 |
words, not abbreviations. Keywords and text are in the ISO 8859-1
|
|
Packit |
0ba690 |
(Latin-1) character set (a superset of regular ASCII) and can not
|
|
Packit |
0ba690 |
contain NUL characters, and should not contain control or other
|
|
Packit |
0ba690 |
unprintable characters. To make the comments widely readable, stick
|
|
Packit |
0ba690 |
with basic ASCII, and avoid machine specific character set extensions
|
|
Packit |
0ba690 |
like the IBM-PC character set. The keyword must be present, but
|
|
Packit |
0ba690 |
you can leave off the text string on non-compressed pairs.
|
|
Packit |
0ba690 |
Compressed pairs must have a text string, as only the text string
|
|
Packit |
0ba690 |
is compressed anyway, so the compression would be meaningless.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG supports modification time via the png_time structure. Two
|
|
Packit |
0ba690 |
conversion routines are provided, png_convert_from_time_t() for
|
|
Packit |
0ba690 |
time_t and png_convert_from_struct_tm() for struct tm. The
|
|
Packit |
0ba690 |
time_t routine uses gmtime(). You don't have to use either of
|
|
Packit |
0ba690 |
these, but if you wish to fill in the png_time structure directly,
|
|
Packit |
0ba690 |
you should provide the time in universal time (GMT) if possible
|
|
Packit |
0ba690 |
instead of your local time. Note that the year number is the full
|
|
Packit |
0ba690 |
year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
|
|
Packit |
0ba690 |
that months start with 1.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you want to store the time of the original image creation, you should
|
|
Packit |
0ba690 |
use a plain tEXt chunk with the "Creation Time" keyword. This is
|
|
Packit |
0ba690 |
necessary because the "creation time" of a PNG image is somewhat vague,
|
|
Packit |
0ba690 |
depending on whether you mean the PNG file, the time the image was
|
|
Packit |
0ba690 |
created in a non-PNG format, a still photo from which the image was
|
|
Packit |
0ba690 |
scanned, or possibly the subject matter itself. In order to facilitate
|
|
Packit |
0ba690 |
machine-readable dates, it is recommended that the "Creation Time"
|
|
Packit |
0ba690 |
tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
|
|
Packit |
0ba690 |
although this isn't a requirement. Unlike the tIME chunk, the
|
|
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0ba690 |
"Creation Time" tEXt chunk is not expected to be automatically changed
|
|
Packit |
0ba690 |
by the software. To facilitate the use of RFC 1123 dates, a function
|
|
Packit |
0ba690 |
png_convert_to_rfc1123(png_timep) is provided to convert from PNG
|
|
Packit |
0ba690 |
time to an RFC 1123 format string.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Writing unknown chunks
|
|
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0ba690 |
|
|
Packit |
0ba690 |
You can use the png_set_unknown_chunks function to queue up chunks
|
|
Packit |
0ba690 |
for writing. You give it a chunk name, raw data, and a size; that's
|
|
Packit |
0ba690 |
all there is to it. The chunks will be written by the next following
|
|
Packit |
0ba690 |
png_write_info_before_PLTE, png_write_info, or png_write_end function.
|
|
Packit |
0ba690 |
Any chunks previously read into the info structure's unknown-chunk
|
|
Packit |
0ba690 |
list will also be written out in a sequence that satisfies the PNG
|
|
Packit |
0ba690 |
specification's ordering rules.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS The high-level write interface
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
At this point there are two ways to proceed; through the high-level
|
|
Packit |
0ba690 |
write interface, or through a sequence of low-level write operations.
|
|
Packit |
0ba690 |
You can use the high-level interface if your image data is present
|
|
Packit |
0ba690 |
in the info structure. All defined output
|
|
Packit |
0ba690 |
transformations are permitted, enabled by the following masks.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG_TRANSFORM_IDENTITY No transformation
|
|
Packit |
0ba690 |
PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
|
|
Packit |
0ba690 |
PNG_TRANSFORM_PACKSWAP Change order of packed
|
|
Packit |
0ba690 |
pixels to LSB first
|
|
Packit |
0ba690 |
PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|
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0ba690 |
PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|
Packit |
0ba690 |
sBIT depth
|
|
Packit |
0ba690 |
PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|
Packit |
0ba690 |
to BGRA
|
|
Packit |
0ba690 |
PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|
Packit |
0ba690 |
to AG
|
|
Packit |
0ba690 |
PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|
Packit |
0ba690 |
to transparency
|
|
Packit |
0ba690 |
PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|
Packit |
0ba690 |
PNG_TRANSFORM_STRIP_FILLER Strip out filler
|
|
Packit |
0ba690 |
bytes (deprecated).
|
|
Packit |
0ba690 |
PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
|
|
Packit |
0ba690 |
filler bytes
|
|
Packit |
0ba690 |
PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
|
|
Packit |
0ba690 |
filler bytes
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you have valid image data in the info structure (you can use
|
|
Packit |
0ba690 |
png_set_rows() to put image data in the info structure), simply do this:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_write_png(png_ptr, info_ptr, png_transforms, NULL)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where png_transforms is an integer containing the bitwise OR of some set of
|
|
Packit |
0ba690 |
transformation flags. This call is equivalent to png_write_info(),
|
|
Packit |
0ba690 |
followed the set of transformations indicated by the transform mask,
|
|
Packit |
0ba690 |
then png_write_image(), and finally png_write_end().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
(The final parameter of this call is not yet used. Someday it might point
|
|
Packit |
0ba690 |
to transformation parameters required by some future output transform.)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You must use png_transforms and not call any png_set_transform() functions
|
|
Packit |
0ba690 |
when you use png_write_png().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS The low-level write interface
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are going the low-level route instead, you are now ready to
|
|
Packit |
0ba690 |
write all the file information up to the actual image data. You do
|
|
Packit |
0ba690 |
this with a call to png_write_info().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_write_info(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Note that there is one transformation you may need to do before
|
|
Packit |
0ba690 |
png_write_info(). In PNG files, the alpha channel in an image is the
|
|
Packit |
0ba690 |
level of opacity. If your data is supplied as a level of transparency,
|
|
Packit |
0ba690 |
you can invert the alpha channel before you write it, so that 0 is
|
|
Packit |
0ba690 |
fully transparent and 255 (in 8-bit or paletted images) or 65535
|
|
Packit |
0ba690 |
(in 16-bit images) is fully opaque, with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_invert_alpha(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This must appear before png_write_info() instead of later with the
|
|
Packit |
0ba690 |
other transformations because in the case of paletted images the tRNS
|
|
Packit |
0ba690 |
chunk data has to be inverted before the tRNS chunk is written. If
|
|
Packit |
0ba690 |
your image is not a paletted image, the tRNS data (which in such cases
|
|
Packit |
0ba690 |
represents a single color to be rendered as transparent) won't need to
|
|
Packit |
0ba690 |
be changed, and you can safely do this transformation after your
|
|
Packit |
0ba690 |
png_write_info() call.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you need to write a private chunk that you want to appear before
|
|
Packit |
0ba690 |
the PLTE chunk when PLTE is present, you can write the PNG info in
|
|
Packit |
0ba690 |
two steps, and insert code to write your own chunk between them:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_write_info_before_PLTE(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
png_set_unknown_chunks(png_ptr, info_ptr, ...);
|
|
Packit |
0ba690 |
png_write_info(png_ptr, info_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
After you've written the file information, you can set up the library
|
|
Packit |
0ba690 |
to handle any special transformations of the image data. The various
|
|
Packit |
0ba690 |
ways to transform the data will be described in the order that they
|
|
Packit |
0ba690 |
should occur. This is important, as some of these change the color
|
|
Packit |
0ba690 |
type and/or bit depth of the data, and some others only work on
|
|
Packit |
0ba690 |
certain color types and bit depths. Even though each transformation
|
|
Packit |
0ba690 |
checks to see if it has data that it can do something with, you should
|
|
Packit |
0ba690 |
make sure to only enable a transformation if it will be valid for the
|
|
Packit |
0ba690 |
data. For example, don't swap red and blue on grayscale data.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
|
|
Packit |
0ba690 |
the library to strip input data that has 4 or 8 bytes per pixel down
|
|
Packit |
0ba690 |
to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
|
|
Packit |
0ba690 |
bytes per pixel).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
|
|
Packit |
0ba690 |
PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
|
|
Packit |
0ba690 |
is stored XRGB or RGBX.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|
Packit |
0ba690 |
they can, resulting in, for example, 8 pixels per byte for 1 bit files.
|
|
Packit |
0ba690 |
If the data is supplied at 1 pixel per byte, use this code, which will
|
|
Packit |
0ba690 |
correctly pack the pixels into a single byte:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_packing(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
|
|
Packit |
0ba690 |
data is of another bit depth, you can write an sBIT chunk into the
|
|
Packit |
0ba690 |
file so that decoders can recover the original data if desired.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* Set the true bit depth of the image data */
|
|
Packit |
0ba690 |
if (color_type & PNG_COLOR_MASK_COLOR)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
sig_bit.red = true_bit_depth;
|
|
Packit |
0ba690 |
sig_bit.green = true_bit_depth;
|
|
Packit |
0ba690 |
sig_bit.blue = true_bit_depth;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
else
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
sig_bit.gray = true_bit_depth;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
if (color_type & PNG_COLOR_MASK_ALPHA)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
sig_bit.alpha = true_bit_depth;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_sBIT(png_ptr, info_ptr, &sig_bit);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If the data is stored in the row buffer in a bit depth other than
|
|
Packit |
0ba690 |
one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
|
|
Packit |
0ba690 |
this will scale the values to appear to be the correct bit depth as
|
|
Packit |
0ba690 |
is required by PNG.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_shift(png_ptr, &sig_bit);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files store 16 bit pixels in network byte order (big-endian,
|
|
Packit |
0ba690 |
ie. most significant bits first). This code would be used if they are
|
|
Packit |
0ba690 |
supplied the other way (little-endian, i.e. least significant bits
|
|
Packit |
0ba690 |
first, the way PCs store them):
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (bit_depth > 8)
|
|
Packit |
0ba690 |
png_set_swap(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|
Packit |
0ba690 |
need to change the order the pixels are packed into bytes, you can use:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (bit_depth < 8)
|
|
Packit |
0ba690 |
png_set_packswap(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files store 3 color pixels in red, green, blue order. This code
|
|
Packit |
0ba690 |
would be used if they are supplied as blue, green, red:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_bgr(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
PNG files describe monochrome as black being zero and white being
|
|
Packit |
0ba690 |
one. This code would be used if the pixels are supplied with this reversed
|
|
Packit |
0ba690 |
(black being one and white being zero):
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_invert_mono(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Finally, you can write your own transformation function if none of
|
|
Packit |
0ba690 |
the existing ones meets your needs. This is done by setting a callback
|
|
Packit |
0ba690 |
with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_write_user_transform_fn(png_ptr,
|
|
Packit |
0ba690 |
write_transform_fn);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You must supply the function
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
void write_transform_fn(png_ptr ptr, row_info_ptr
|
|
Packit |
0ba690 |
row_info, png_bytep data)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
See pngtest.c for a working example. Your function will be called
|
|
Packit |
0ba690 |
before any of the other transformations are processed.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You can also set up a pointer to a user structure for use by your
|
|
Packit |
0ba690 |
callback function.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The user_channels and user_depth parameters of this function are ignored
|
|
Packit |
0ba690 |
when writing; you can set them to zero as shown.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You can retrieve the pointer via the function png_get_user_transform_ptr().
|
|
Packit |
0ba690 |
For example:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
voidp write_user_transform_ptr =
|
|
Packit |
0ba690 |
png_get_user_transform_ptr(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
It is possible to have libpng flush any pending output, either manually,
|
|
Packit |
0ba690 |
or automatically after a certain number of lines have been written. To
|
|
Packit |
0ba690 |
flush the output stream a single time call:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_write_flush(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
and to have libpng flush the output stream periodically after a certain
|
|
Packit |
0ba690 |
number of scanlines have been written, call:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_flush(png_ptr, nrows);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Note that the distance between rows is from the last time png_write_flush()
|
|
Packit |
0ba690 |
was called, or the first row of the image if it has never been called.
|
|
Packit |
0ba690 |
So if you write 50 lines, and then png_set_flush 25, it will flush the
|
|
Packit |
0ba690 |
output on the next scanline, and every 25 lines thereafter, unless
|
|
Packit |
0ba690 |
png_write_flush() is called before 25 more lines have been written.
|
|
Packit |
0ba690 |
If nrows is too small (less than about 10 lines for a 640 pixel wide
|
|
Packit |
0ba690 |
RGB image) the image compression may decrease noticeably (although this
|
|
Packit |
0ba690 |
may be acceptable for real-time applications). Infrequent flushing will
|
|
Packit |
0ba690 |
only degrade the compression performance by a few percent over images
|
|
Packit |
0ba690 |
that do not use flushing.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Writing the image data
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
That's it for the transformations. Now you can write the image data.
|
|
Packit |
0ba690 |
The simplest way to do this is in one function call. If you have the
|
|
Packit |
0ba690 |
whole image in memory, you can just call png_write_image() and libpng
|
|
Packit |
0ba690 |
will write the image. You will need to pass in an array of pointers to
|
|
Packit |
0ba690 |
each row. This function automatically handles interlacing, so you don't
|
|
Packit |
0ba690 |
need to call png_set_interlace_handling() or call this function multiple
|
|
Packit |
0ba690 |
times, or any of that other stuff necessary with png_write_rows().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_write_image(png_ptr, row_pointers);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
where row_pointers is:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_byte *row_pointers[height];
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You can point to void or char or whatever you use for pixels.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you don't want to write the whole image at once, you can
|
|
Packit |
0ba690 |
use png_write_rows() instead. If the file is not interlaced,
|
|
Packit |
0ba690 |
this is simple:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_write_rows(png_ptr, row_pointers,
|
|
Packit |
0ba690 |
number_of_rows);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
row_pointers is the same as in the png_write_image() call.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are just writing one row at a time, you can do this with
|
|
Packit |
0ba690 |
a single row_pointer instead of an array of row_pointers:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_bytep row_pointer = row;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_write_row(png_ptr, row_pointer);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
When the file is interlaced, things can get a good deal more complicated.
|
|
Packit |
0ba690 |
The only currently (as of the PNG Specification version 1.2, dated July
|
|
Packit |
0ba690 |
1999) defined interlacing scheme for PNG files is the "Adam7" interlace
|
|
Packit |
0ba690 |
scheme, that breaks down an image into seven smaller images of varying
|
|
Packit |
0ba690 |
size. libpng will build these images for you, or you can do them
|
|
Packit |
0ba690 |
yourself. If you want to build them yourself, see the PNG specification
|
|
Packit |
0ba690 |
for details of which pixels to write when.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you don't want libpng to handle the interlacing details, just
|
|
Packit |
0ba690 |
use png_set_interlace_handling() and call png_write_rows() the
|
|
Packit |
0ba690 |
correct number of times to write all seven sub-images.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you want libpng to build the sub-images, call this before you start
|
|
Packit |
0ba690 |
writing any rows:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
number_of_passes =
|
|
Packit |
0ba690 |
png_set_interlace_handling(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This will return the number of passes needed. Currently, this is seven,
|
|
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0ba690 |
but may change if another interlace type is added.
|
|
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0ba690 |
|
|
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0ba690 |
Then write the complete image number_of_passes times.
|
|
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0ba690 |
|
|
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0ba690 |
png_write_rows(png_ptr, row_pointers,
|
|
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0ba690 |
number_of_rows);
|
|
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0ba690 |
|
|
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0ba690 |
As some of these rows are not used, and thus return immediately, you may
|
|
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0ba690 |
want to read about interlacing in the PNG specification, and only update
|
|
Packit |
0ba690 |
the rows that are actually used.
|
|
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0ba690 |
|
|
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0ba690 |
.SS Finishing a sequential write
|
|
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0ba690 |
|
|
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0ba690 |
After you are finished writing the image, you should finish writing
|
|
Packit |
0ba690 |
the file. If you are interested in writing comments or time, you should
|
|
Packit |
0ba690 |
pass an appropriately filled png_info pointer. If you are not interested,
|
|
Packit |
0ba690 |
you can pass NULL.
|
|
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0ba690 |
|
|
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0ba690 |
png_write_end(png_ptr, info_ptr);
|
|
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0ba690 |
|
|
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0ba690 |
When you are done, you can free all memory used by libpng like this:
|
|
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0ba690 |
|
|
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0ba690 |
png_destroy_write_struct(&png_ptr, &info_ptr);
|
|
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0ba690 |
|
|
Packit |
0ba690 |
It is also possible to individually free the info_ptr members that
|
|
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0ba690 |
point to libpng-allocated storage with the following function:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_free_data(png_ptr, info_ptr, mask, seq)
|
|
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0ba690 |
mask - identifies data to be freed, a mask
|
|
Packit |
0ba690 |
containing the bitwise OR of one or
|
|
Packit |
0ba690 |
more of
|
|
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0ba690 |
PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|
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0ba690 |
PNG_FREE_HIST, PNG_FREE_ICCP,
|
|
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0ba690 |
PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|
Packit |
0ba690 |
PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|
Packit |
0ba690 |
PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|
Packit |
0ba690 |
or simply PNG_FREE_ALL
|
|
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0ba690 |
seq - sequence number of item to be freed
|
|
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0ba690 |
(\-1 for all items)
|
|
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0ba690 |
|
|
Packit |
0ba690 |
This function may be safely called when the relevant storage has
|
|
Packit |
0ba690 |
already been freed, or has not yet been allocated, or was allocated
|
|
Packit |
0ba690 |
by the user and not by libpng, and will in those cases do nothing.
|
|
Packit |
0ba690 |
The "seq" parameter is ignored if only one item of the selected data
|
|
Packit |
0ba690 |
type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
|
|
Packit |
0ba690 |
are allowed for the data type identified in the mask, such as text or
|
|
Packit |
0ba690 |
sPLT, only the n'th item in the structure is freed, where n is "seq".
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you allocated data such as a palette that you passed in to libpng
|
|
Packit |
0ba690 |
with png_set_*, you must not free it until just before the call to
|
|
Packit |
0ba690 |
png_destroy_write_struct().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The default behavior is only to free data that was allocated internally
|
|
Packit |
0ba690 |
by libpng. This can be changed, so that libpng will not free the data,
|
|
Packit |
0ba690 |
or so that it will free data that was allocated by the user with png_malloc()
|
|
Packit |
0ba690 |
or png_zalloc() and passed in via a png_set_*() function, with
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_data_freer(png_ptr, info_ptr, freer, mask)
|
|
Packit |
0ba690 |
mask - which data elements are affected
|
|
Packit |
0ba690 |
same choices as in png_free_data()
|
|
Packit |
0ba690 |
freer - one of
|
|
Packit |
0ba690 |
PNG_DESTROY_WILL_FREE_DATA
|
|
Packit |
0ba690 |
PNG_SET_WILL_FREE_DATA
|
|
Packit |
0ba690 |
PNG_USER_WILL_FREE_DATA
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
For example, to transfer responsibility for some data from a read structure
|
|
Packit |
0ba690 |
to a write structure, you could use
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_data_freer(read_ptr, read_info_ptr,
|
|
Packit |
0ba690 |
PNG_USER_WILL_FREE_DATA,
|
|
Packit |
0ba690 |
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|
Packit |
0ba690 |
png_data_freer(write_ptr, write_info_ptr,
|
|
Packit |
0ba690 |
PNG_DESTROY_WILL_FREE_DATA,
|
|
Packit |
0ba690 |
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
thereby briefly reassigning responsibility for freeing to the user but
|
|
Packit |
0ba690 |
immediately afterwards reassigning it once more to the write_destroy
|
|
Packit |
0ba690 |
function. Having done this, it would then be safe to destroy the read
|
|
Packit |
0ba690 |
structure and continue to use the PLTE, tRNS, and hIST data in the write
|
|
Packit |
0ba690 |
structure.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This function only affects data that has already been allocated.
|
|
Packit |
0ba690 |
You can call this function before calling after the png_set_*() functions
|
|
Packit |
0ba690 |
to control whether the user or png_destroy_*() is supposed to free the data.
|
|
Packit |
0ba690 |
When the user assumes responsibility for libpng-allocated data, the
|
|
Packit |
0ba690 |
application must use
|
|
Packit |
0ba690 |
png_free() to free it, and when the user transfers responsibility to libpng
|
|
Packit |
0ba690 |
for data that the user has allocated, the user must have used png_malloc()
|
|
Packit |
0ba690 |
or png_zalloc() to allocate it.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|
Packit |
0ba690 |
separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|
Packit |
0ba690 |
because when libpng fills a png_text structure it combines these members with
|
|
Packit |
0ba690 |
the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|
Packit |
0ba690 |
if you transfer responsibility for free'ing text_ptr from libpng to your
|
|
Packit |
0ba690 |
application, your application must not separately free those members.
|
|
Packit |
0ba690 |
For a more compact example of writing a PNG image, see the file example.c.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH V. Modifying/Customizing libpng:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
There are two issues here. The first is changing how libpng does
|
|
Packit |
0ba690 |
standard things like memory allocation, input/output, and error handling.
|
|
Packit |
0ba690 |
The second deals with more complicated things like adding new chunks,
|
|
Packit |
0ba690 |
adding new transformations, and generally changing how libpng works.
|
|
Packit |
0ba690 |
Both of those are compile-time issues; that is, they are generally
|
|
Packit |
0ba690 |
determined at the time the code is written, and there is rarely a need
|
|
Packit |
0ba690 |
to provide the user with a means of changing them.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Memory allocation, input/output, and error handling
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
All of the memory allocation, input/output, and error handling in libpng
|
|
Packit |
0ba690 |
goes through callbacks that are user-settable. The default routines are
|
|
Packit |
0ba690 |
in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
|
|
Packit |
0ba690 |
these functions, call the appropriate png_set_*_fn() function.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Memory allocation is done through the functions png_malloc(), png_calloc(),
|
|
Packit |
0ba690 |
and png_free(). These currently just call the standard C functions.
|
|
Packit |
0ba690 |
png_calloc() calls png_malloc() and then png_memset() to clear the newly
|
|
Packit |
0ba690 |
allocated memory to zero. If your pointers can't access more then 64K
|
|
Packit |
0ba690 |
at a time, you will want to set MAXSEG_64K in zlib.h. Since it is
|
|
Packit |
0ba690 |
unlikely that the method of handling memory allocation on a platform
|
|
Packit |
0ba690 |
will change between applications, these functions must be modified in
|
|
Packit |
0ba690 |
the library at compile time. If you prefer to use a different method
|
|
Packit |
0ba690 |
of allocating and freeing data, you can use png_create_read_struct_2() or
|
|
Packit |
0ba690 |
png_create_write_struct_2() to register your own functions as described
|
|
Packit |
0ba690 |
above. These functions also provide a void pointer that can be retrieved
|
|
Packit |
0ba690 |
via
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
mem_ptr=png_get_mem_ptr(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Your replacement memory functions must have prototypes as follows:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_voidp malloc_fn(png_structp png_ptr,
|
|
Packit |
0ba690 |
png_size_t size);
|
|
Packit |
0ba690 |
void free_fn(png_structp png_ptr, png_voidp ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Your malloc_fn() must return NULL in case of failure. The png_malloc()
|
|
Packit |
0ba690 |
function will normally call png_error() if it receives a NULL from the
|
|
Packit |
0ba690 |
system memory allocator or from your replacement malloc_fn().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Your free_fn() will never be called with a NULL ptr, since libpng's
|
|
Packit |
0ba690 |
png_free() checks for NULL before calling free_fn().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Input/Output in libpng is done through png_read() and png_write(),
|
|
Packit |
0ba690 |
which currently just call fread() and fwrite(). The FILE * is stored in
|
|
Packit |
0ba690 |
png_struct and is initialized via png_init_io(). If you wish to change
|
|
Packit |
0ba690 |
the method of I/O, the library supplies callbacks that you can set
|
|
Packit |
0ba690 |
through the function png_set_read_fn() and png_set_write_fn() at run
|
|
Packit |
0ba690 |
time, instead of calling the png_init_io() function. These functions
|
|
Packit |
0ba690 |
also provide a void pointer that can be retrieved via the function
|
|
Packit |
0ba690 |
png_get_io_ptr(). For example:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_read_fn(png_structp read_ptr,
|
|
Packit |
0ba690 |
voidp read_io_ptr, png_rw_ptr read_data_fn)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_write_fn(png_structp write_ptr,
|
|
Packit |
0ba690 |
voidp write_io_ptr, png_rw_ptr write_data_fn,
|
|
Packit |
0ba690 |
png_flush_ptr output_flush_fn);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
voidp read_io_ptr = png_get_io_ptr(read_ptr);
|
|
Packit |
0ba690 |
voidp write_io_ptr = png_get_io_ptr(write_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The replacement I/O functions must have prototypes as follows:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
void user_read_data(png_structp png_ptr,
|
|
Packit |
0ba690 |
png_bytep data, png_size_t length);
|
|
Packit |
0ba690 |
void user_write_data(png_structp png_ptr,
|
|
Packit |
0ba690 |
png_bytep data, png_size_t length);
|
|
Packit |
0ba690 |
void user_flush_data(png_structp png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The user_read_data() function is responsible for detecting and
|
|
Packit |
0ba690 |
handling end-of-data errors.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Supplying NULL for the read, write, or flush functions sets them back
|
|
Packit |
0ba690 |
to using the default C stream functions, which expect the io_ptr to
|
|
Packit |
0ba690 |
point to a standard *FILE structure. It is probably a mistake
|
|
Packit |
0ba690 |
to use NULL for one of write_data_fn and output_flush_fn but not both
|
|
Packit |
0ba690 |
of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
|
|
Packit |
0ba690 |
It is an error to read from a write stream, and vice versa.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Error handling in libpng is done through png_error() and png_warning().
|
|
Packit |
0ba690 |
Errors handled through png_error() are fatal, meaning that png_error()
|
|
Packit |
0ba690 |
should never return to its caller. Currently, this is handled via
|
|
Packit |
0ba690 |
setjmp() and longjmp() (unless you have compiled libpng with
|
|
Packit |
0ba690 |
PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
|
|
Packit |
0ba690 |
but you could change this to do things like exit() if you should wish.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
On non-fatal errors, png_warning() is called
|
|
Packit |
0ba690 |
to print a warning message, and then control returns to the calling code.
|
|
Packit |
0ba690 |
By default png_error() and png_warning() print a message on stderr via
|
|
Packit |
0ba690 |
fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
|
|
Packit |
0ba690 |
(because you don't want the messages) or PNG_NO_STDIO defined (because
|
|
Packit |
0ba690 |
fprintf() isn't available). If you wish to change the behavior of the error
|
|
Packit |
0ba690 |
functions, you will need to set up your own message callbacks. These
|
|
Packit |
0ba690 |
functions are normally supplied at the time that the png_struct is created.
|
|
Packit |
0ba690 |
It is also possible to redirect errors and warnings to your own replacement
|
|
Packit |
0ba690 |
functions after png_create_*_struct() has been called by calling:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_error_fn(png_structp png_ptr,
|
|
Packit |
0ba690 |
png_voidp error_ptr, png_error_ptr error_fn,
|
|
Packit |
0ba690 |
png_error_ptr warning_fn);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_voidp error_ptr = png_get_error_ptr(png_ptr);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If NULL is supplied for either error_fn or warning_fn, then the libpng
|
|
Packit |
0ba690 |
default function will be used, calling fprintf() and/or longjmp() if a
|
|
Packit |
0ba690 |
problem is encountered. The replacement error functions should have
|
|
Packit |
0ba690 |
parameters as follows:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
void user_error_fn(png_structp png_ptr,
|
|
Packit |
0ba690 |
png_const_charp error_msg);
|
|
Packit |
0ba690 |
void user_warning_fn(png_structp png_ptr,
|
|
Packit |
0ba690 |
png_const_charp warning_msg);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The motivation behind using setjmp() and longjmp() is the C++ throw and
|
|
Packit |
0ba690 |
catch exception handling methods. This makes the code much easier to write,
|
|
Packit |
0ba690 |
as there is no need to check every return code of every function call.
|
|
Packit |
0ba690 |
However, there are some uncertainties about the status of local variables
|
|
Packit |
0ba690 |
after a longjmp, so the user may want to be careful about doing anything
|
|
Packit |
0ba690 |
after setjmp returns non-zero besides returning itself. Consult your
|
|
Packit |
0ba690 |
compiler documentation for more details. For an alternative approach, you
|
|
Packit |
0ba690 |
may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Custom chunks
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you need to read or write custom chunks, you may need to get deeper
|
|
Packit |
0ba690 |
into the libpng code. The library now has mechanisms for storing
|
|
Packit |
0ba690 |
and writing chunks of unknown type; you can even declare callbacks
|
|
Packit |
0ba690 |
for custom chunks. However, this may not be good enough if the
|
|
Packit |
0ba690 |
library code itself needs to know about interactions between your
|
|
Packit |
0ba690 |
chunk and existing `intrinsic' chunks.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you need to write a new intrinsic chunk, first read the PNG
|
|
Packit |
0ba690 |
specification. Acquire a first level of understanding of how it works.
|
|
Packit |
0ba690 |
Pay particular attention to the sections that describe chunk names,
|
|
Packit |
0ba690 |
and look at how other chunks were designed, so you can do things
|
|
Packit |
0ba690 |
similarly. Second, check out the sections of libpng that read and
|
|
Packit |
0ba690 |
write chunks. Try to find a chunk that is similar to yours and use
|
|
Packit |
0ba690 |
it as a template. More details can be found in the comments inside
|
|
Packit |
0ba690 |
the code. It is best to handle unknown chunks in a generic method,
|
|
Packit |
0ba690 |
via callback functions, instead of by modifying libpng functions.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you wish to write your own transformation for the data, look through
|
|
Packit |
0ba690 |
the part of the code that does the transformations, and check out some of
|
|
Packit |
0ba690 |
the simpler ones to get an idea of how they work. Try to find a similar
|
|
Packit |
0ba690 |
transformation to the one you want to add and copy off of it. More details
|
|
Packit |
0ba690 |
can be found in the comments inside the code itself.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Configuring for 16 bit platforms
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You will want to look into zconf.h to tell zlib (and thus libpng) that
|
|
Packit |
0ba690 |
it cannot allocate more then 64K at a time. Even if you can, the memory
|
|
Packit |
0ba690 |
won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Configuring for DOS
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
For DOS users who only have access to the lower 640K, you will
|
|
Packit |
0ba690 |
have to limit zlib's memory usage via a png_set_compression_mem_level()
|
|
Packit |
0ba690 |
call. See zlib.h or zconf.h in the zlib library for more information.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Configuring for Medium Model
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Libpng's support for medium model has been tested on most of the popular
|
|
Packit |
0ba690 |
compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
|
|
Packit |
0ba690 |
defined, and FAR gets defined to far in pngconf.h, and you should be
|
|
Packit |
0ba690 |
all set. Everything in the library (except for zlib's structure) is
|
|
Packit |
0ba690 |
expecting far data. You must use the typedefs with the p or pp on
|
|
Packit |
0ba690 |
the end for pointers (or at least look at them and be careful). Make
|
|
Packit |
0ba690 |
note that the rows of data are defined as png_bytepp, which is an
|
|
Packit |
0ba690 |
unsigned char far * far *.
|
|
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0ba690 |
|
|
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0ba690 |
.SS Configuring for gui/windowing platforms:
|
|
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0ba690 |
|
|
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0ba690 |
You will need to write new error and warning functions that use the GUI
|
|
Packit |
0ba690 |
interface, as described previously, and set them to be the error and
|
|
Packit |
0ba690 |
warning functions at the time that png_create_*_struct() is called,
|
|
Packit |
0ba690 |
in order to have them available during the structure initialization.
|
|
Packit |
0ba690 |
They can be changed later via png_set_error_fn(). On some compilers,
|
|
Packit |
0ba690 |
you may also have to change the memory allocators (png_malloc, etc.).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Configuring for compiler xxx:
|
|
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0ba690 |
|
|
Packit |
0ba690 |
All includes for libpng are in pngconf.h. If you need to add, change
|
|
Packit |
0ba690 |
or delete an include, this is the place to do it.
|
|
Packit |
0ba690 |
The includes that are not needed outside libpng are protected by the
|
|
Packit |
0ba690 |
PNG_INTERNAL definition, which is only defined for those routines inside
|
|
Packit |
0ba690 |
libpng itself. The files in libpng proper only include png.h, which
|
|
Packit |
0ba690 |
includes pngconf.h.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Configuring zlib:
|
|
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0ba690 |
|
|
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0ba690 |
There are special functions to configure the compression. Perhaps the
|
|
Packit |
0ba690 |
most useful one changes the compression level, which currently uses
|
|
Packit |
0ba690 |
input compression values in the range 0 - 9. The library normally
|
|
Packit |
0ba690 |
uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
|
|
Packit |
0ba690 |
have shown that for a large majority of images, compression values in
|
|
Packit |
0ba690 |
the range 3-6 compress nearly as well as higher levels, and do so much
|
|
Packit |
0ba690 |
faster. For online applications it may be desirable to have maximum speed
|
|
Packit |
0ba690 |
(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
|
|
Packit |
0ba690 |
specify no compression (Z_NO_COMPRESSION = 0), but this would create
|
|
Packit |
0ba690 |
files larger than just storing the raw bitmap. You can specify the
|
|
Packit |
0ba690 |
compression level by calling:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_compression_level(png_ptr, level);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Another useful one is to reduce the memory level used by the library.
|
|
Packit |
0ba690 |
The memory level defaults to 8, but it can be lowered if you are
|
|
Packit |
0ba690 |
short on memory (running DOS, for example, where you only have 640K).
|
|
Packit |
0ba690 |
Note that the memory level does have an effect on compression; among
|
|
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0ba690 |
other things, lower levels will result in sections of incompressible
|
|
Packit |
0ba690 |
data being emitted in smaller stored blocks, with a correspondingly
|
|
Packit |
0ba690 |
larger relative overhead of up to 15% in the worst case.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_compression_mem_level(png_ptr, level);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The other functions are for configuring zlib. They are not recommended
|
|
Packit |
0ba690 |
for normal use and may result in writing an invalid PNG file. See
|
|
Packit |
0ba690 |
zlib.h for more information on what these mean.
|
|
Packit |
0ba690 |
|
|
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0ba690 |
png_set_compression_strategy(png_ptr,
|
|
Packit |
0ba690 |
strategy);
|
|
Packit |
0ba690 |
png_set_compression_window_bits(png_ptr,
|
|
Packit |
0ba690 |
window_bits);
|
|
Packit |
0ba690 |
png_set_compression_method(png_ptr, method);
|
|
Packit |
0ba690 |
png_set_compression_buffer_size(png_ptr, size);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Controlling row filtering
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you want to control whether libpng uses filtering or not, which
|
|
Packit |
0ba690 |
filters are used, and how it goes about picking row filters, you
|
|
Packit |
0ba690 |
can call one of these functions. The selection and configuration
|
|
Packit |
0ba690 |
of row filters can have a significant impact on the size and
|
|
Packit |
0ba690 |
encoding speed and a somewhat lesser impact on the decoding speed
|
|
Packit |
0ba690 |
of an image. Filtering is enabled by default for RGB and grayscale
|
|
Packit |
0ba690 |
images (with and without alpha), but not for paletted images nor
|
|
Packit |
0ba690 |
for any images with bit depths less than 8 bits/pixel.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The 'method' parameter sets the main filtering method, which is
|
|
Packit |
0ba690 |
currently only '0' in the PNG 1.2 specification. The 'filters'
|
|
Packit |
0ba690 |
parameter sets which filter(s), if any, should be used for each
|
|
Packit |
0ba690 |
scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
|
|
Packit |
0ba690 |
to turn filtering on and off, respectively.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
|
|
Packit |
0ba690 |
PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
|
|
Packit |
0ba690 |
ORed together with '|' to specify one or more filters to use.
|
|
Packit |
0ba690 |
These filters are described in more detail in the PNG specification.
|
|
Packit |
0ba690 |
If you intend to change the filter type during the course of writing
|
|
Packit |
0ba690 |
the image, you should start with flags set for all of the filters
|
|
Packit |
0ba690 |
you intend to use so that libpng can initialize its internal
|
|
Packit |
0ba690 |
structures appropriately for all of the filter types. (Note that this
|
|
Packit |
0ba690 |
means the first row must always be adaptively filtered, because libpng
|
|
Packit |
0ba690 |
currently does not allocate the filter buffers until png_write_row()
|
|
Packit |
0ba690 |
is called for the first time.)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
filters = PNG_FILTER_NONE | PNG_FILTER_SUB
|
|
Packit |
0ba690 |
PNG_FILTER_UP | PNG_FILTER_AVG |
|
|
Packit |
0ba690 |
PNG_FILTER_PAETH | PNG_ALL_FILTERS;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
|
|
Packit |
0ba690 |
filters);
|
|
Packit |
0ba690 |
The second parameter can also be
|
|
Packit |
0ba690 |
PNG_INTRAPIXEL_DIFFERENCING if you are
|
|
Packit |
0ba690 |
writing a PNG to be embedded in a MNG
|
|
Packit |
0ba690 |
datastream. This parameter must be the
|
|
Packit |
0ba690 |
same as the value of filter_method used
|
|
Packit |
0ba690 |
in png_set_IHDR().
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Removing unwanted object code
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
There are a bunch of #define's in pngconf.h that control what parts of
|
|
Packit |
0ba690 |
libpng are compiled. All the defines end in _SUPPORTED. If you are
|
|
Packit |
0ba690 |
never going to use a capability, you can change the #define to #undef
|
|
Packit |
0ba690 |
before recompiling libpng and save yourself code and data space, or
|
|
Packit |
0ba690 |
you can turn off individual capabilities with defines that begin with
|
|
Packit |
0ba690 |
PNG_NO_.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You can also turn all of the transforms and ancillary chunk capabilities
|
|
Packit |
0ba690 |
off en masse with compiler directives that define
|
|
Packit |
0ba690 |
PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
|
|
Packit |
0ba690 |
or all four,
|
|
Packit |
0ba690 |
along with directives to turn on any of the capabilities that you do
|
|
Packit |
0ba690 |
want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
|
|
Packit |
0ba690 |
transformations but still leave the library fully capable of reading
|
|
Packit |
0ba690 |
and writing PNG files with all known public chunks. Use of the
|
|
Packit |
0ba690 |
PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
|
|
Packit |
0ba690 |
that is incapable of reading or writing ancillary chunks. If you are
|
|
Packit |
0ba690 |
not using the progressive reading capability, you can turn that off
|
|
Packit |
0ba690 |
with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
|
|
Packit |
0ba690 |
capability, which you'll still have).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
All the reading and writing specific code are in separate files, so the
|
|
Packit |
0ba690 |
linker should only grab the files it needs. However, if you want to
|
|
Packit |
0ba690 |
make sure, or if you are building a stand alone library, all the
|
|
Packit |
0ba690 |
reading files start with pngr and all the writing files start with
|
|
Packit |
0ba690 |
pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
|
|
Packit |
0ba690 |
are used for both reading and writing, and always need to be included.
|
|
Packit |
0ba690 |
The progressive reader is in pngpread.c
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you are creating or distributing a dynamically linked library (a .so
|
|
Packit |
0ba690 |
or DLL file), you should not remove or disable any parts of the library,
|
|
Packit |
0ba690 |
as this will cause applications linked with different versions of the
|
|
Packit |
0ba690 |
library to fail if they call functions not available in your library.
|
|
Packit |
0ba690 |
The size of the library itself should not be an issue, because only
|
|
Packit |
0ba690 |
those sections that are actually used will be loaded into memory.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SS Requesting debug printout
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The macro definition PNG_DEBUG can be used to request debugging
|
|
Packit |
0ba690 |
printout. Set it to an integer value in the range 0 to 3. Higher
|
|
Packit |
0ba690 |
numbers result in increasing amounts of debugging information. The
|
|
Packit |
0ba690 |
information is printed to the "stderr" file, unless another file
|
|
Packit |
0ba690 |
name is specified in the PNG_DEBUG_FILE macro definition.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
When PNG_DEBUG > 0, the following functions (macros) become available:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_debug(level, message)
|
|
Packit |
0ba690 |
png_debug1(level, message, p1)
|
|
Packit |
0ba690 |
png_debug2(level, message, p1, p2)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
in which "level" is compared to PNG_DEBUG to decide whether to print
|
|
Packit |
0ba690 |
the message, "message" is the formatted string to be printed,
|
|
Packit |
0ba690 |
and p1 and p2 are parameters that are to be embedded in the string
|
|
Packit |
0ba690 |
according to printf-style formatting directives. For example,
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_debug1(2, "foo=%d", foo);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
is expanded to
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if(PNG_DEBUG > 2)
|
|
Packit |
0ba690 |
fprintf(PNG_DEBUG_FILE, "foo=%d\en", foo);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
|
|
Packit |
0ba690 |
can still use PNG_DEBUG to control your own debugging:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
#ifdef PNG_DEBUG
|
|
Packit |
0ba690 |
fprintf(stderr, ...
|
|
Packit |
0ba690 |
#endif
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
|
|
Packit |
0ba690 |
having level = 0 will be printed. There aren't any such statements in
|
|
Packit |
0ba690 |
this version of libpng, but if you insert some they will be printed.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH VI. MNG support
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The MNG specification (available at http://www.libpng.org/pub/mng) allows
|
|
Packit |
0ba690 |
certain extensions to PNG for PNG images that are embedded in MNG datastreams.
|
|
Packit |
0ba690 |
Libpng can support some of these extensions. To enable them, use the
|
|
Packit |
0ba690 |
png_permit_mng_features() function:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
feature_set = png_permit_mng_features(png_ptr, mask)
|
|
Packit |
0ba690 |
mask is a png_uint_32 containing the bitwise OR of the
|
|
Packit |
0ba690 |
features you want to enable. These include
|
|
Packit |
0ba690 |
PNG_FLAG_MNG_EMPTY_PLTE
|
|
Packit |
0ba690 |
PNG_FLAG_MNG_FILTER_64
|
|
Packit |
0ba690 |
PNG_ALL_MNG_FEATURES
|
|
Packit |
0ba690 |
feature_set is a png_uint_32 that is the bitwise AND of
|
|
Packit |
0ba690 |
your mask with the set of MNG features that is
|
|
Packit |
0ba690 |
supported by the version of libpng that you are using.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
It is an error to use this function when reading or writing a standalone
|
|
Packit |
0ba690 |
PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
|
|
Packit |
0ba690 |
in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
|
|
Packit |
0ba690 |
and the MHDR and MEND chunks. Libpng does not provide support for these
|
|
Packit |
0ba690 |
or any other MNG chunks; your application must provide its own support for
|
|
Packit |
0ba690 |
them. You may wish to consider using libmng (available at
|
|
Packit |
0ba690 |
http://www.libmng.com) instead.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH VII. Changes to Libpng from version 0.88
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
It should be noted that versions of libpng later than 0.96 are not
|
|
Packit |
0ba690 |
distributed by the original libpng author, Guy Schalnat, nor by
|
|
Packit |
0ba690 |
Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
|
|
Packit |
0ba690 |
distributed versions 0.89 through 0.96, but rather by another member
|
|
Packit |
0ba690 |
of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
|
|
Packit |
0ba690 |
still alive and well, but they have moved on to other things.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The old libpng functions png_read_init(), png_write_init(),
|
|
Packit |
0ba690 |
png_info_init(), png_read_destroy(), and png_write_destroy() have been
|
|
Packit |
0ba690 |
moved to PNG_INTERNAL in version 0.95 to discourage their use. These
|
|
Packit |
0ba690 |
functions will be removed from libpng version 2.0.0.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The preferred method of creating and initializing the libpng structures is
|
|
Packit |
0ba690 |
via the png_create_read_struct(), png_create_write_struct(), and
|
|
Packit |
0ba690 |
png_create_info_struct() because they isolate the size of the structures
|
|
Packit |
0ba690 |
from the application, allow version error checking, and also allow the
|
|
Packit |
0ba690 |
use of custom error handling routines during the initialization, which
|
|
Packit |
0ba690 |
the old functions do not. The functions png_read_destroy() and
|
|
Packit |
0ba690 |
png_write_destroy() do not actually free the memory that libpng
|
|
Packit |
0ba690 |
allocated for these structs, but just reset the data structures, so they
|
|
Packit |
0ba690 |
can be used instead of png_destroy_read_struct() and
|
|
Packit |
0ba690 |
png_destroy_write_struct() if you feel there is too much system overhead
|
|
Packit |
0ba690 |
allocating and freeing the png_struct for each image read.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Setting the error callbacks via png_set_message_fn() before
|
|
Packit |
0ba690 |
png_read_init() as was suggested in libpng-0.88 is no longer supported
|
|
Packit |
0ba690 |
because this caused applications that do not use custom error functions
|
|
Packit |
0ba690 |
to fail if the png_ptr was not initialized to zero. It is still possible
|
|
Packit |
0ba690 |
to set the error callbacks AFTER png_read_init(), or to change them with
|
|
Packit |
0ba690 |
png_set_error_fn(), which is essentially the same function, but with a new
|
|
Packit |
0ba690 |
name to force compilation errors with applications that try to use the old
|
|
Packit |
0ba690 |
method.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Support for the sCAL, iCCP, iTXt, and sPLT chunks was added at libpng-1.0.6;
|
|
Packit |
0ba690 |
however, iTXt support was not enabled by default.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Starting with version 1.0.7, you can find out which version of the library
|
|
Packit |
0ba690 |
you are using at run-time:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_uint_32 libpng_vn = png_access_version_number();
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The number libpng_vn is constructed from the major version, minor
|
|
Packit |
0ba690 |
version with leading zero, and release number with leading zero,
|
|
Packit |
0ba690 |
(e.g., libpng_vn for version 1.0.7 is 10007).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
You can also check which version of png.h you used when compiling your
|
|
Packit |
0ba690 |
application:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_uint_32 application_vn = PNG_LIBPNG_VER;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Support for user memory management was enabled by default. To
|
|
Packit |
0ba690 |
accomplish this, the functions png_create_read_struct_2(),
|
|
Packit |
0ba690 |
png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
|
|
Packit |
0ba690 |
png_malloc_default(), and png_free_default() were added.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Support for the iTXt chunk has been enabled by default as of
|
|
Packit |
0ba690 |
version 1.2.41.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Support for certain MNG features was enabled.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Support for numbered error messages was added. However, we never got
|
|
Packit |
0ba690 |
around to actually numbering the error messages. The function
|
|
Packit |
0ba690 |
png_set_strip_error_numbers() was added (Note: the prototype for this
|
|
Packit |
0ba690 |
function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
|
|
Packit |
0ba690 |
builds of libpng-1.2.15. It was restored in libpng-1.2.36).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The png_malloc_warn() function was added at libpng-1.2.3. This issues
|
|
Packit |
0ba690 |
a png_warning and returns NULL instead of aborting when it fails to
|
|
Packit |
0ba690 |
acquire the requested memory allocation.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Support for setting user limits on image width and height was enabled
|
|
Packit |
0ba690 |
by default. The functions png_set_user_limits(), png_get_user_width_max(),
|
|
Packit |
0ba690 |
and png_get_user_height_max() were added at libpng-1.2.6.
|
|
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0ba690 |
|
|
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The png_set_add_alpha() function was added at libpng-1.2.7.
|
|
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0ba690 |
|
|
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The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
|
|
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0ba690 |
Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
|
|
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0ba690 |
tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
|
|
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0ba690 |
deprecated.
|
|
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0ba690 |
|
|
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A number of macro definitions in support of runtime selection of
|
|
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assembler code features (especially Intel MMX code support) were
|
|
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added at libpng-1.2.0:
|
|
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0ba690 |
|
|
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PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
|
|
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PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
|
|
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PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
|
|
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0ba690 |
PNG_ASM_FLAG_MMX_READ_INTERLACE
|
|
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0ba690 |
PNG_ASM_FLAG_MMX_READ_FILTER_SUB
|
|
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0ba690 |
PNG_ASM_FLAG_MMX_READ_FILTER_UP
|
|
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0ba690 |
PNG_ASM_FLAG_MMX_READ_FILTER_AVG
|
|
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PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
|
|
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PNG_ASM_FLAGS_INITIALIZED
|
|
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PNG_MMX_READ_FLAGS
|
|
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PNG_MMX_FLAGS
|
|
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PNG_MMX_WRITE_FLAGS
|
|
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PNG_MMX_FLAGS
|
|
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0ba690 |
|
|
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We added the following functions in support of runtime
|
|
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selection of assembler code features:
|
|
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0ba690 |
|
|
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0ba690 |
png_get_mmx_flagmask()
|
|
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png_set_mmx_thresholds()
|
|
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0ba690 |
png_get_asm_flags()
|
|
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0ba690 |
png_get_mmx_bitdepth_threshold()
|
|
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0ba690 |
png_get_mmx_rowbytes_threshold()
|
|
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0ba690 |
png_set_asm_flags()
|
|
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|
|
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We replaced all of these functions with simple stubs in libpng-1.2.20,
|
|
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when the Intel assembler code was removed due to a licensing issue.
|
|
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|
|
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These macros are deprecated:
|
|
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|
|
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PNG_READ_TRANSFORMS_NOT_SUPPORTED
|
|
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0ba690 |
PNG_PROGRESSIVE_READ_NOT_SUPPORTED
|
|
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0ba690 |
PNG_NO_SEQUENTIAL_READ_SUPPORTED
|
|
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0ba690 |
PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
|
|
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0ba690 |
PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
|
|
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PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
|
|
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|
|
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They have been replaced, respectively, by:
|
|
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|
|
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PNG_NO_READ_TRANSFORMS
|
|
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PNG_NO_PROGRESSIVE_READ
|
|
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PNG_NO_SEQUENTIAL_READ
|
|
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0ba690 |
PNG_NO_WRITE_TRANSFORMS
|
|
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PNG_NO_READ_ANCILLARY_CHUNKS
|
|
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0ba690 |
PNG_NO_WRITE_ANCILLARY_CHUNKS
|
|
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0ba690 |
|
|
Packit |
0ba690 |
PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
|
|
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0ba690 |
deprecated since libpng-1.0.16 and libpng-1.2.6.
|
|
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0ba690 |
|
|
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0ba690 |
The function
|
|
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0ba690 |
png_check_sig(sig, num)
|
|
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0ba690 |
was replaced with
|
|
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0ba690 |
!png_sig_cmp(sig, 0, num)
|
|
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0ba690 |
It has been deprecated since libpng-0.90.
|
|
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0ba690 |
|
|
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The function
|
|
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0ba690 |
png_set_gray_1_2_4_to_8()
|
|
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0ba690 |
which also expands tRNS to alpha was replaced with
|
|
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0ba690 |
png_set_expand_gray_1_2_4_to_8()
|
|
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0ba690 |
which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
|
|
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0ba690 |
|
|
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.SH IX. (Omitted)
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Starting with libpng-1.2.54, attempting to set an over-length
|
|
Packit |
0ba690 |
PLTE chunk is an error. Previously this requirement of the PNG specification
|
|
Packit |
0ba690 |
was not enforced, and the palette was always limited to 256 entries.
|
|
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0ba690 |
An over-length PLTE chunk found in an input PNG is silently truncated.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH X. Detecting libpng
|
|
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0ba690 |
|
|
Packit |
0ba690 |
The png_get_io_ptr() function has been present since libpng-0.88, has never
|
|
Packit |
0ba690 |
changed, and is unaffected by conditional compilation macros. It is the
|
|
Packit |
0ba690 |
best choice for use in configure scripts for detecting the presence of any
|
|
Packit |
0ba690 |
libpng version since 0.88. In an autoconf "configure.in" you could use
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
AC_CHECK_LIB(png, png_get_io_ptr, ...
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH XI. Source code repository
|
|
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0ba690 |
|
|
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0ba690 |
Since about February 2009, version 1.2.34, libpng has been under "git" source
|
|
Packit |
0ba690 |
control. The git repository was built from old libpng-x.y.z.tar.gz files
|
|
Packit |
0ba690 |
going back to version 0.70. You can access the git repository (read only)
|
|
Packit |
0ba690 |
at
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
git://git.code.sf.net/p/libpng/code
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
or you can browse it with a web browser by selecting the "code" button at
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
https://sourceforge.net/projects/libpng/
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Patches can be sent to glennrp at users.sourceforge.net or to
|
|
Packit |
0ba690 |
png-mng-implement at lists.sourceforge.net or you can upload them to
|
|
Packit |
0ba690 |
the libpng bug tracker at
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
http://libpng.sourceforge.net
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH XII. Coding style
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Our coding style is similar to the "Allman" style
|
|
Packit |
0ba690 |
(See http://en.wikipedia.org/wiki/Indent_style#Allman_style), with curly
|
|
Packit |
0ba690 |
braces on separate lines:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (condition)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
action;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
else if (another condition)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
another action;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The braces can be omitted from simple one-line actions:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
if (condition)
|
|
Packit |
0ba690 |
return (0);
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
We use 3-space indentation, except for continued statements which
|
|
Packit |
0ba690 |
are usually indented the same as the first line of the statement
|
|
Packit |
0ba690 |
plus four more spaces.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
For macro definitions we use 2-space indentation, always leaving the "#"
|
|
Packit |
0ba690 |
in the first column.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
#ifndef PNG_NO_FEATURE
|
|
Packit |
0ba690 |
# ifndef PNG_FEATURE_SUPPORTED
|
|
Packit |
0ba690 |
# define PNG_FEATURE_SUPPORTED
|
|
Packit |
0ba690 |
# endif
|
|
Packit |
0ba690 |
#endif
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Comments appear with the leading "/*" at the same indentation as
|
|
Packit |
0ba690 |
the statement that follows the comment:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* Single-line comment */
|
|
Packit |
0ba690 |
statement;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* Multiple-line
|
|
Packit |
0ba690 |
* comment
|
|
Packit |
0ba690 |
*/
|
|
Packit |
0ba690 |
statement;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Very short comments can be placed at the end of the statement
|
|
Packit |
0ba690 |
to which they pertain:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
statement; /* comment */
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
We don't use C++ style ("//") comments. We have, however,
|
|
Packit |
0ba690 |
used them in the past in some now-abandoned MMX assembler
|
|
Packit |
0ba690 |
code.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Functions and their curly braces are not indented, and
|
|
Packit |
0ba690 |
exported functions are marked with PNGAPI:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* This is a public function that is visible to
|
|
Packit |
0ba690 |
* application programers. It does thus-and-so.
|
|
Packit |
0ba690 |
*/
|
|
Packit |
0ba690 |
void PNGAPI
|
|
Packit |
0ba690 |
png_exported_function(png_ptr, png_info, foo)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
body;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The prototypes for all exported functions appear in png.h,
|
|
Packit |
0ba690 |
above the comment that says
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* Maintainer: Put new public prototypes here ... */
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
We mark all non-exported functions with "/* PRIVATE */"":
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
void /* PRIVATE */
|
|
Packit |
0ba690 |
png_non_exported_function(png_ptr, png_info, foo)
|
|
Packit |
0ba690 |
{
|
|
Packit |
0ba690 |
body;
|
|
Packit |
0ba690 |
}
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The prototypes for non-exported functions (except for those in
|
|
Packit |
0ba690 |
pngtest) appear in
|
|
Packit |
0ba690 |
the PNG_INTERNAL section of png.h
|
|
Packit |
0ba690 |
above the comment that says
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
/* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The names of all exported functions and variables begin
|
|
Packit |
0ba690 |
with "png_", and all publicly visible C preprocessor
|
|
Packit |
0ba690 |
macros begin with "PNG".
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
We put a space after each comma and after each semicolon
|
|
Packit |
0ba690 |
in "for" statments, and we put spaces before and after each
|
|
Packit |
0ba690 |
C binary operator and after "for" or "while". We don't
|
|
Packit |
0ba690 |
put a space between a typecast and the expression being
|
|
Packit |
0ba690 |
cast, nor do we put one between a function name and the
|
|
Packit |
0ba690 |
left parenthesis that follows it:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
for (i = 2; i > 0; --i)
|
|
Packit |
0ba690 |
y[i] = a(x) + (int)b;
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
We prefer #ifdef and #ifndef to #if defined() and if !defined()
|
|
Packit |
0ba690 |
when there is only one macro being tested.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
We do not use the TAB character for indentation in the C sources.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Lines do not exceed 80 characters.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Other rules can be inferred by inspecting the libpng source.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH XIII. Y2K Compliance in libpng
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Since the PNG Development group is an ad-hoc body, we can't make
|
|
Packit |
0ba690 |
an official declaration.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This is your unofficial assurance that libpng from version 0.71 and
|
|
Packit |
0ba690 |
upward through 1.2.57 are Y2K compliant. It is my belief that earlier
|
|
Packit |
0ba690 |
versions were also Y2K compliant.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Libpng only has three year fields. One is a 2-byte unsigned integer that
|
|
Packit |
0ba690 |
will hold years up to 65535. The other two hold the date in text
|
|
Packit |
0ba690 |
format, and will hold years up to 9999.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The integer is
|
|
Packit |
0ba690 |
"png_uint_16 year" in png_time_struct.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The strings are
|
|
Packit |
0ba690 |
"png_charp time_buffer" in png_struct and
|
|
Packit |
0ba690 |
"near_time_buffer", which is a local character string in png.c.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
There are seven time-related functions:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
png_convert_to_rfc_1123() in png.c
|
|
Packit |
0ba690 |
(formerly png_convert_to_rfc_1152() in error)
|
|
Packit |
0ba690 |
png_convert_from_struct_tm() in pngwrite.c, called
|
|
Packit |
0ba690 |
in pngwrite.c
|
|
Packit |
0ba690 |
png_convert_from_time_t() in pngwrite.c
|
|
Packit |
0ba690 |
png_get_tIME() in pngget.c
|
|
Packit |
0ba690 |
png_handle_tIME() in pngrutil.c, called in pngread.c
|
|
Packit |
0ba690 |
png_set_tIME() in pngset.c
|
|
Packit |
0ba690 |
png_write_tIME() in pngwutil.c, called in pngwrite.c
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
All appear to handle dates properly in a Y2K environment. The
|
|
Packit |
0ba690 |
png_convert_from_time_t() function calls gmtime() to convert from system
|
|
Packit |
0ba690 |
clock time, which returns (year - 1900), which we properly convert to
|
|
Packit |
0ba690 |
the full 4-digit year. There is a possibility that applications using
|
|
Packit |
0ba690 |
libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
|
|
Packit |
0ba690 |
function, or that they are incorrectly passing only a 2-digit year
|
|
Packit |
0ba690 |
instead of "year - 1900" into the png_convert_from_struct_tm() function,
|
|
Packit |
0ba690 |
but this is not under our control. The libpng documentation has always
|
|
Packit |
0ba690 |
stated that it works with 4-digit years, and the APIs have been
|
|
Packit |
0ba690 |
documented as such.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
|
|
Packit |
0ba690 |
integer to hold the year, and can hold years as large as 65535.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
zlib, upon which libpng depends, is also Y2K compliant. It contains
|
|
Packit |
0ba690 |
no date-related code.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Glenn Randers-Pehrson
|
|
Packit |
0ba690 |
libpng maintainer
|
|
Packit |
0ba690 |
PNG Development Group
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.SH NOTE
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Note about libpng version numbers:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Due to various miscommunications, unforeseen code incompatibilities
|
|
Packit |
0ba690 |
and occasional factors outside the authors' control, version numbering
|
|
Packit |
0ba690 |
on the library has not always been consistent and straightforward.
|
|
Packit |
0ba690 |
The following table summarizes matters since version 0.89c, which was
|
|
Packit |
0ba690 |
the first widely used release:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
source png.h png.h shared-lib
|
|
Packit |
0ba690 |
version string int version
|
|
Packit |
0ba690 |
------- ------ ----- ----------
|
|
Packit |
0ba690 |
0.89c "1.0 beta 3" 0.89 89 1.0.89
|
|
Packit |
0ba690 |
0.90 "1.0 beta 4" 0.90 90 0.90 [should have been 2.0.90]
|
|
Packit |
0ba690 |
0.95 "1.0 beta 5" 0.95 95 0.95 [should have been 2.0.95]
|
|
Packit |
0ba690 |
0.96 "1.0 beta 6" 0.96 96 0.96 [should have been 2.0.96]
|
|
Packit |
0ba690 |
0.97b "1.00.97 beta 7" 1.00.97 97 1.0.1 [should have been 2.0.97]
|
|
Packit |
0ba690 |
0.97c 0.97 97 2.0.97
|
|
Packit |
0ba690 |
0.98 0.98 98 2.0.98
|
|
Packit |
0ba690 |
0.99 0.99 98 2.0.99
|
|
Packit |
0ba690 |
0.99a-m 0.99 99 2.0.99
|
|
Packit |
0ba690 |
1.00 1.00 100 2.1.0 [100 should be 10000]
|
|
Packit |
0ba690 |
1.0.0 (from here on, the 100 2.1.0 [100 should be 10000]
|
|
Packit |
0ba690 |
1.0.1 png.h string is 10001 2.1.0
|
|
Packit |
0ba690 |
1.0.1a-e identical to the 10002 from here on, the shared library
|
|
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0ba690 |
1.0.2 source version) 10002 is 2.V where V is the source code
|
|
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1.0.2a-b 10003 version, except as noted.
|
|
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1.0.3 10003
|
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1.0.3a-d 10004
|
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1.0.4 10004
|
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1.0.4a-f 10005
|
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1.0.5 (+ 2 patches) 10005
|
|
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1.0.5a-d 10006
|
|
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1.0.5e-r 10100 (not source compatible)
|
|
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1.0.5s-v 10006 (not binary compatible)
|
|
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1.0.6 (+ 3 patches) 10006 (still binary incompatible)
|
|
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1.0.6d-f 10007 (still binary incompatible)
|
|
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1.0.6g 10007
|
|
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1.0.6h 10007 10.6h (testing xy.z so-numbering)
|
|
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1.0.6i 10007 10.6i
|
|
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1.0.6j 10007 2.1.0.6j (incompatible with 1.0.0)
|
|
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1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14 (binary compatible)
|
|
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1.0.7beta15-18 1 10007 2.1.0.7beta15-18 (binary compatible)
|
|
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1.0.7rc1-2 1 10007 2.1.0.7rc1-2 (binary compatible)
|
|
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1.0.7 1 10007 (still compatible)
|
|
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...
|
|
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1.0.19 10 10019 10.so.0.19[.0]
|
|
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...
|
|
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0ba690 |
1.0.67 10 10067 10.so.0.67[.0]
|
|
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1.2.57 13 10257 12.so.0.57[.0]
|
|
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|
|
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Henceforth the source version will match the shared-library minor
|
|
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and patch numbers; the shared-library major version number will be
|
|
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0ba690 |
used for changes in backward compatibility, as it is intended. The
|
|
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PNG_PNGLIB_VER macro, which is not used within libpng but is available
|
|
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0ba690 |
for applications, is an unsigned integer of the form xyyzz corresponding
|
|
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0ba690 |
to the source version x.y.z (leading zeros in y and z). Beta versions
|
|
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0ba690 |
were given the previous public release number plus a letter, until
|
|
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0ba690 |
version 1.0.6j; from then on they were given the upcoming public
|
|
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release number plus "betaNN" or "rcNN".
|
|
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|
|
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.SH "SEE ALSO"
|
|
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.IR libpngpf(3) ", " png(5)
|
|
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.LP
|
|
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.IR libpng :
|
|
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.IP
|
|
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http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
|
|
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http://www.libpng.org/pub/png
|
|
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|
|
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.LP
|
|
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.IR zlib :
|
|
Packit |
0ba690 |
.IP
|
|
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0ba690 |
(generally) at the same location as
|
|
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.I libpng
|
|
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0ba690 |
or at
|
|
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0ba690 |
.br
|
|
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0ba690 |
ftp://ftp.info-zip.org/pub/infozip/zlib
|
|
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0ba690 |
|
|
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0ba690 |
.LP
|
|
Packit |
0ba690 |
.IR PNG specification: RFC 2083
|
|
Packit |
0ba690 |
.IP
|
|
Packit |
0ba690 |
(generally) at the same location as
|
|
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0ba690 |
.I libpng
|
|
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0ba690 |
or at
|
|
Packit |
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.br
|
|
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ftp://ftp.rfc-editor.org:/in-notes/rfc2083.txt
|
|
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.br
|
|
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or (as a W3C Recommendation) at
|
|
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.br
|
|
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0ba690 |
http://www.w3.org/TR/REC-png.html
|
|
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0ba690 |
|
|
Packit |
0ba690 |
.LP
|
|
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0ba690 |
In the case of any inconsistency between the PNG specification
|
|
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0ba690 |
and this library, the specification takes precedence.
|
|
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0ba690 |
|
|
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.SH AUTHORS
|
|
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This man page: Glenn Randers-Pehrson
|
|
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<glennrp at users.sourceforge.net>
|
|
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|
|
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0ba690 |
The contributing authors would like to thank all those who helped
|
|
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with testing, bug fixes, and patience. This wouldn't have been
|
|
Packit |
0ba690 |
possible without all of you.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Thanks to Frank J. T. Wojcik for helping with the documentation.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Libpng version 1.2.57 - December 29, 2016:
|
|
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0ba690 |
Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
|
|
Packit |
0ba690 |
Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Supported by the PNG development group
|
|
Packit |
0ba690 |
.br
|
|
Packit |
0ba690 |
png-mng-implement at lists.sf.net
|
|
Packit |
0ba690 |
(subscription required; visit
|
|
Packit |
0ba690 |
png-mng-implement at lists.sourceforge.net (subscription required; visit
|
|
Packit |
0ba690 |
https://lists.sourceforge.net/lists/listinfo/png-mng-implement
|
|
Packit |
0ba690 |
to subscribe).
|
|
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0ba690 |
|
|
Packit |
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.SH NOTICES:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
This copy of the libpng notices is provided for your convenience. In case of
|
|
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0ba690 |
any discrepancy between this copy and the notices in the file png.h that is
|
|
Packit |
0ba690 |
included in the libpng distribution, the latter shall prevail.
|
|
Packit |
0ba690 |
|
|
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0ba690 |
COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
If you modify libpng you may insert additional notices immediately following
|
|
Packit |
0ba690 |
this sentence.
|
|
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0ba690 |
|
|
Packit |
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This code is released under the libpng license.
|
|
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0ba690 |
|
|
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0ba690 |
libpng versions 1.0.7, July 1, 2000, through 1.2.57, December 29, 2016, are
|
|
Packit |
0ba690 |
Copyright (c) 2000-2002, 2004, 2006-2016 Glenn Randers-Pehrson, are
|
|
Packit |
0ba690 |
derived from libpng-1.0.6, and are distributed according to the same
|
|
Packit |
0ba690 |
disclaimer and license as libpng-1.0.6 with the following individuals
|
|
Packit |
0ba690 |
added to the list of Contributing Authors:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Simon-Pierre Cadieux
|
|
Packit |
0ba690 |
Eric S. Raymond
|
|
Packit |
0ba690 |
Cosmin Truta
|
|
Packit |
0ba690 |
Gilles Vollant
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
and with the following additions to the disclaimer:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
There is no warranty against interference with your enjoyment of the
|
|
Packit |
0ba690 |
library or against infringement. There is no warranty that our
|
|
Packit |
0ba690 |
efforts or the library will fulfill any of your particular purposes
|
|
Packit |
0ba690 |
or needs. This library is provided with all faults, and the entire
|
|
Packit |
0ba690 |
risk of satisfactory quality, performance, accuracy, and effort is with
|
|
Packit |
0ba690 |
the user.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
|
|
Packit |
0ba690 |
Copyright (c) 1998-2000 Glenn Randers-Pehrson, are derived from
|
|
Packit |
0ba690 |
libpng-0.96, and are distributed according to the same disclaimer and
|
|
Packit |
0ba690 |
license as libpng-0.96, with the following individuals added to the list
|
|
Packit |
0ba690 |
of Contributing Authors:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Tom Lane
|
|
Packit |
0ba690 |
Glenn Randers-Pehrson
|
|
Packit |
0ba690 |
Willem van Schaik
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
libpng versions 0.89, June 1996, through 0.96, May 1997, are
|
|
Packit |
0ba690 |
Copyright (c) 1996-1997 Andreas Dilger, are derived from libpng-0.88,
|
|
Packit |
0ba690 |
and are distributed according to the same disclaimer and license as
|
|
Packit |
0ba690 |
libpng-0.88, with the following individuals added to the list of
|
|
Packit |
0ba690 |
Contributing Authors:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
John Bowler
|
|
Packit |
0ba690 |
Kevin Bracey
|
|
Packit |
0ba690 |
Sam Bushell
|
|
Packit |
0ba690 |
Magnus Holmgren
|
|
Packit |
0ba690 |
Greg Roelofs
|
|
Packit |
0ba690 |
Tom Tanner
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
libpng versions 0.5, May 1995, through 0.88, January 1996, are
|
|
Packit |
0ba690 |
Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
For the purposes of this copyright and license, "Contributing Authors"
|
|
Packit |
0ba690 |
is defined as the following set of individuals:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Andreas Dilger
|
|
Packit |
0ba690 |
Dave Martindale
|
|
Packit |
0ba690 |
Guy Eric Schalnat
|
|
Packit |
0ba690 |
Paul Schmidt
|
|
Packit |
0ba690 |
Tim Wegner
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The PNG Reference Library is supplied "AS IS". The Contributing Authors
|
|
Packit |
0ba690 |
and Group 42, Inc. disclaim all warranties, expressed or implied,
|
|
Packit |
0ba690 |
including, without limitation, the warranties of merchantability and of
|
|
Packit |
0ba690 |
fitness for any purpose. The Contributing Authors and Group 42, Inc.
|
|
Packit |
0ba690 |
assume no liability for direct, indirect, incidental, special, exemplary,
|
|
Packit |
0ba690 |
or consequential damages, which may result from the use of the PNG
|
|
Packit |
0ba690 |
Reference Library, even if advised of the possibility of such damage.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Permission is hereby granted to use, copy, modify, and distribute this
|
|
Packit |
0ba690 |
source code, or portions hereof, for any purpose, without fee, subject
|
|
Packit |
0ba690 |
to the following restrictions:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
1. The origin of this source code must not be misrepresented.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
2. Altered versions must be plainly marked as such and must not
|
|
Packit |
0ba690 |
be misrepresented as being the original source.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
3. This Copyright notice may not be removed or altered from any
|
|
Packit |
0ba690 |
source or altered source distribution.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
The Contributing Authors and Group 42, Inc. specifically permit, without
|
|
Packit |
0ba690 |
fee, and encourage the use of this source code as a component to
|
|
Packit |
0ba690 |
supporting the PNG file format in commercial products. If you use this
|
|
Packit |
0ba690 |
source code in a product, acknowledgment is not required but would be
|
|
Packit |
0ba690 |
appreciated.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
END OF COPYRIGHT NOTICE, DISCLAIMER, and LICENSE.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
A "png_get_copyright" function is available, for convenient use in "about"
|
|
Packit |
0ba690 |
boxes and the like:
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
printf("%s", png_get_copyright(NULL));
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Also, the PNG logo (in PNG format, of course) is supplied in the
|
|
Packit |
0ba690 |
files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Libpng is OSI Certified Open Source Software. OSI Certified Open Source is
|
|
Packit |
0ba690 |
a certification mark of the Open Source Initiative. OSI has not addressed
|
|
Packit |
0ba690 |
the additional disclaimers inserted at version 1.0.7.
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
Glenn Randers-Pehrson
|
|
Packit |
0ba690 |
glennrp at users.sourceforge.net
|
|
Packit |
0ba690 |
December 29, 2016
|
|
Packit |
0ba690 |
|
|
Packit |
0ba690 |
.\" end of man page
|
|
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0ba690 |
|