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<title>TIFFRGBAImage</title>
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<body>
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TIFFRGBAImage
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NAME
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SYNOPSIS
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DESCRIPTION
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ALTERNATE RASTER FORMATS
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SIMULTANEOUS RASTER STORE AND DISPLAY
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SUPPORTING ADDITIONAL TIFF FORMATS
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NOTES
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RETURN VALUES
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DIAGNOSTICS
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SEE ALSO
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NAME
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       cols="2" cellspacing="0" cellpadding="0">
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TIFFRGBAImageOK, TIFFRGBAImageBegin, TIFFRGBAImageGet,
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TIFFRGBAImageEnd − read and decode an image into a
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raster
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SYNOPSIS
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       cols="2" cellspacing="0" cellpadding="0">
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#include <tiffio.h>
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typedef unsigned char TIFFRGBValue; typedef struct
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_TIFFRGBAImage TIFFRGBAImage;
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int TIFFRGBAImageOK(TIFF *tif, char
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emsg[1024])
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int TIFFRGBAImageBegin(TIFFRGBAImage *img,
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TIFF* tif, int stopOnError,
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char emsg[1024])
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int TIFFRGBAImageGet(TIFFRGBAImage *img,
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uint32* raster, uint32 width ,
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uint32 height)
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void TIFFRGBAImageEnd(TIFFRGBAImage
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*img)
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DESCRIPTION
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The routines described here provide a high-level
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interface through which <small>TIFF</small> images may be
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read into memory. Images may be strip- or tile-based and
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have a variety of different characteristics: bits/sample,
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samples/pixel, photometric, etc. Decoding state is
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encapsulated in a TIFFRGBAImage structure making it
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possible to capture state for multiple images and quickly
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switch between them. The target raster format can be
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customized to a particular application’s needs by
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installing custom routines that manipulate image data
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according to application requirements.
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The default usage for these routines is: check if an
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image can be processed using TIFFRGBAImageOK,
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construct a decoder state block using
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TIFFRGBAImageBegin, read and decode an image into a
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target raster using TIFFRGBAImageGet, and then
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release resources using TIFFRGBAImageEnd.
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TIFFRGBAImageGet can be called multiple times to
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decode an image using different state parameters. If
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multiple images are to be displayed and there is not enough
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space for each of the decoded rasters, multiple state blocks
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can be managed and then calls can be made to
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TIFFRGBAImageGet as needed to display an image.
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The generated raster is assumed to be an array of
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width times height 32-bit entries, where
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width must be less than or equal to the width of the
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image (height may be any non-zero size). If the
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raster dimensions are smaller than the image, the image data
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is cropped to the raster bounds. If the raster height is
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greater than that of the image, then the image data are
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placed in the lower part of the raster. (Note that the
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raster is assume to be organized such that the pixel at
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location (x,y) is
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raster[y*width+x]; with the
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raster origin in the lower-left hand corner.)
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Raster pixels are 8-bit packed red, green, blue, alpha
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samples. The macros TIFFGetR, TIFFGetG,
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TIFFGetB, and TIFFGetA should be used to
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access individual samples. Images without Associated Alpha
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matting information have a constant Alpha of 1.0 (255).
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TIFFRGBAImageGet converts non-8-bit images by
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scaling sample values. Palette, grayscale, bilevel,
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<small>CMYK</small> , and YCbCr images are converted to
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<small>RGB</small> transparently. Raster pixels are returned
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uncorrected by any colorimetry information present in the
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directory.
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The parameter stopOnError specifies how to act if
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an error is encountered while reading the image. If
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stopOnError is non-zero, then an error will terminate
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the operation; otherwise TIFFRGBAImageGet will
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continue processing data until all the possible data in the
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image have been requested.
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ALTERNATE RASTER FORMATS
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       cols="2" cellspacing="0" cellpadding="0">
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To use the core support for reading and processing
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<small>TIFF</small> images, but write the resulting raster
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data in a different format one need only override the
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‘‘put methods’’ used to store
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raster data. These methods are are defined in the
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TIFFRGBAImage structure and initially setup by
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TIFFRGBAImageBegin to point to routines that pack
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raster data in the default <small>ABGR</small> pixel format.
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Two different routines are used according to the physical
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organization of the image data in the file:
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PlanarConfiguration=1 (packed samples), and
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PlanarConfiguration=2 (separated samples). Note that
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this mechanism can be used to transform the data before
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storing it in the raster. For example one can convert data
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to colormap indices for display on a colormap display.
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SIMULTANEOUS RASTER STORE AND DISPLAY
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It is simple to display an image as it is being read into
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memory by overriding the put methods as described above for
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supporting alternate raster formats. Simply keep a reference
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to the default put methods setup by
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TIFFRGBAImageBegin and then invoke them before or
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after each display operation. For example, the
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tiffgt(1) utility uses the following put method to
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update the display as the raster is being filled:
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static void
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putContigAndDraw(TIFFRGBAImage* img, uint32* raster,
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    uint32 x, uint32 y, uint32 w, uint32 h,
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    int32 fromskew, int32 toskew,
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    unsigned char* cp)
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{
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    (*putContig)(img, raster, x, y, w, h, fromskew, toskew, cp);
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    if (x+w == width) {
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     w = width;
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     if (img->orientation == ORIENTATION_TOPLEFT)
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         lrectwrite(0, y-(h-1), w-1, y, raster-x-(h-1)*w);
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     else
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         lrectwrite(0, y, w-1, y+h-1, raster);
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    }
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}
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(the original routine provided by the library is saved in
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the variable putContig.)
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SUPPORTING ADDITIONAL TIFF FORMATS
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The TIFFRGBAImage routines support the most
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commonly encountered flavors of <small>TIFF.</small> It is
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possible to extend this support by overriding the
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‘‘get method’’ invoked by
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TIFFRGBAImageGet to read <small>TIFF</small> image
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data. Details of doing this are a bit involved, it is best
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to make a copy of an existing get method and modify it to
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suit the needs of an application.
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NOTES
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       cols="2" cellspacing="0" cellpadding="0">
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Samples must be either 1, 2, 4, 8, or 16 bits.
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Colorimetric samples/pixel must be either 1, 3, or 4 (i.e.
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SamplesPerPixel minus ExtraSamples).
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Palette image colormaps that appear to be incorrectly
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written as 8-bit values are automatically scaled to
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16-bits.
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RETURN VALUES
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       cols="2" cellspacing="0" cellpadding="0">
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All routines return 1 if the operation was successful.
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Otherwise, 0 is returned if an error was encountered and
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stopOnError is zero.
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DIAGNOSTICS
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       cols="2" cellspacing="0" cellpadding="0">
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All error messages are directed to the
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TIFFError(3TIFF) routine.
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Sorry, can not handle %d-bit pictures. The image
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had BitsPerSample other than 1, 2, 4, 8, or 16.
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Sorry, can not handle %d-channel images. The image
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had SamplesPerPixel other than 1, 3, or 4.
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Missing needed "PhotometricInterpretation"
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tag. The image did not have a tag that describes how to
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display the data.
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No "PhotometricInterpretation" tag, assuming
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RGB. The image was missing a tag that describes how to
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display it, but because it has 3 or 4 samples/pixel, it is
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assumed to be <small>RGB.</small>
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No "PhotometricInterpretation" tag, assuming
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min-is-black. The image was missing a tag that describes
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how to display it, but because it has 1 sample/pixel, it is
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assumed to be a grayscale or bilevel image.
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No space for photometric conversion table. There
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was insufficient memory for a table used to convert image
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samples to 8-bit <small>RGB.</small>
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Missing required "Colormap" tag. A
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Palette image did not have a required Colormap
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tag.
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No space for tile buffer. There was insufficient
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memory to allocate an i/o buffer.
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No space for strip buffer. There was insufficient
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memory to allocate an i/o buffer.
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Can not handle format. The image has a format
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(combination of BitsPerSample,
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SamplesPerPixel, and
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PhotometricInterpretation) that can not be
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handled.
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No space for B&W mapping table. There was
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insufficient memory to allocate a table used to map
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grayscale data to <small>RGB.</small>
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No space for Palette mapping table. There was
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insufficient memory to allocate a table used to map data to
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8-bit <small>RGB.</small>
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SEE ALSO
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       cols="2" cellspacing="0" cellpadding="0">
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TIFFOpen(3TIFF), TIFFReadRGBAImage(3TIFF),
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TIFFReadRGBAImageOriented(3TIFF),
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TIFFReadRGBAStrip(3TIFF),
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TIFFReadRGBATile(3TIFF), libtiff(3TIFF)
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Libtiff library home page:
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http://www.simplesystems.org/libtiff/
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</body>
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</html>

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