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<html lang="en">
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<head>
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<title>Using The TIFF Library</title>
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<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
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<meta http-equiv="content-language" content="en">
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<style type="text/css">
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th {text-align: left; vertical-align: top; font-style: italic; font-weight: normal}
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-->
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</style>
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</head>
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<body lang="en" text="#000000" bgcolor="#ffffff" link="#0000ff" alink="#0000ff" vlink="#0000ff">
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Using The TIFF Library
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<tt>libtiff</tt> is a set of C functions (a library) that support
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the manipulation of TIFF image files.
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The library requires an ANSI C compilation environment for building
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and presumes an ANSI C environment for use.
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<tt>libtiff</tt>
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provides interfaces to image data at several layers of abstraction (and cost).
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At the highest level image data can be read into an 8-bit/sample,
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ABGR pixel raster format without regard for the underlying data organization,
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colorspace, or compression scheme. Below this high-level interface
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the library provides scanline-, strip-, and tile-oriented interfaces that
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return data decompressed but otherwise untransformed. These interfaces
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require that the application first identify the organization of stored
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data and select either a strip-based or tile-based API for manipulating
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data. At the lowest level the library
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provides access to the raw uncompressed strips or tiles,
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returning the data exactly as it appears in the file.
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The material presented in this chapter is a basic introduction
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to the capabilities of the library; it is not an attempt to describe
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everything a developer needs to know about the library or about TIFF.
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Detailed information on the interfaces to the library are given in
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the UNIX
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manual pages that accompany this software.
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Michael Still has also written a useful introduction to libtiff for the
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IBM DeveloperWorks site available at
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http://www.ibm.com/developerworks/linux/library/l-libtiff.
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The following sections are found in this chapter:
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How to tell which version you have
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Library Datatypes
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Memory Management
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Error Handling
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Basic File Handling
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TIFF Directories
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TIFF Tags
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TIFF Compression Schemes
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Byte Order
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Data Placement
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TIFFRGBAImage Support
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Scanline-based Image I/O
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Strip-oriented Image I/O
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Tile-oriented Image I/O
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Other Stuff
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How to tell which version you have
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The software version can be found by looking at the file named
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<tt>VERSION</tt>
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that is located at the top of the source tree; the precise alpha number
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is given in the file <tt>dist/tiff.alpha</tt>.
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If you have need to refer to this
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specific software, you should identify it as:
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|
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<tt>TIFF <version> <alpha></tt>
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where <tt><version></tt> is whatever you get from
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<tt>"cat VERSION"</tt> and <tt><alpha></tt> is
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what you get from <tt>"cat dist/tiff.alpha"</tt>.
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Within an application that uses <tt>libtiff</tt> the <tt>TIFFGetVersion</tt>
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routine will return a pointer to a string that contains software version
|
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information.
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The library include file <tt><tiffio.h></tt> contains a C pre-processor
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define <tt>TIFFLIB_VERSION</tt> that can be used to check library
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version compatiblity at compile time.
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Library Datatypes
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<tt>libtiff</tt> defines a portable programming interface through the
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use of a set of C type definitions.
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These definitions, defined in in the files tiff.h and
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tiffio.h,
|
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isolate the <tt>libtiff</tt> API from the characteristics
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of the underlying machine.
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To insure portable code and correct operation, applications that use
|
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<tt>libtiff</tt> should use the typedefs and follow the function
|
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prototypes for the library API.
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Memory Management
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<tt>libtiff</tt> uses a machine-specific set of routines for managing
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dynamically allocated memory.
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<tt>_TIFFmalloc</tt>, <tt>_TIFFrealloc</tt>, and <tt>_TIFFfree</tt>
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mimic the normal ANSI C routines.
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Any dynamically allocated memory that is to be passed into the library
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should be allocated using these interfaces in order to insure pointer
|
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compatibility on machines with a segmented architecture.
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(On 32-bit UNIX systems these routines just call the normal <tt>malloc</tt>,
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<tt>realloc</tt>, and <tt>free</tt> routines in the C library.)
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To deal with segmented pointer issues <tt>libtiff</tt> also provides
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<tt>_TIFFmemcpy</tt>, <tt>_TIFFmemset</tt>, and <tt>_TIFFmemmove</tt>
|
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routines that mimic the equivalent ANSI C routines, but that are
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intended for use with memory allocated through <tt>_TIFFmalloc</tt>
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and <tt>_TIFFrealloc</tt>.
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|
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Error Handling
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<tt>libtiff</tt> handles most errors by returning an invalid/erroneous
|
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value when returning from a function call.
|
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Various diagnostic messages may also be generated by the library.
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All error messages are directed to a single global error handler
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routine that can be specified with a call to <tt>TIFFSetErrorHandler</tt>.
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Likewise warning messages are directed to a single handler routine
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that can be specified with a call to <tt>TIFFSetWarningHandler</tt>
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Basic File Handling
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The library is modeled after the normal UNIX stdio library.
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For example, to read from an existing TIFF image the
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file must first be opened:
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|
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<tt>#include "tiffio.h"
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main()
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{
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TIFF* tif = TIFFOpen("foo.tif", "r");
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... do stuff ...
|
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TIFFClose(tif);
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}</tt>
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The handle returned by <tt>TIFFOpen</tt> is opaque, that is
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the application is not permitted to know about its contents.
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All subsequent library calls for this file must pass the handle
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as an argument.
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To create or overwrite a TIFF image the file is also opened, but with
|
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a <tt>"w"</tt> argument:
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|
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<tt>#include "tiffio.h"
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main()
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{
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TIFF* tif = TIFFOpen("foo.tif", "w");
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... do stuff ...
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TIFFClose(tif);
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}</tt>
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If the file already exists it is first truncated to zero length.
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Note that unlike the stdio library TIFF image files may not be
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opened for both reading and writing;
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there is no support for altering the contents of a TIFF file.
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<tt>libtiff</tt> buffers much information associated with writing a
|
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valid TIFF image. Consequently, when writing a TIFF image it is necessary
|
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to always call <tt>TIFFClose</tt> or <tt>TIFFFlush</tt> to flush any
|
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buffered information to a file. Note that if you call <tt>TIFFClose</tt>
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you do not need to call <tt>TIFFFlush</tt>.
|
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|
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TIFF Directories
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TIFF supports the storage of multiple images in a single file.
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Each image has an associated data structure termed a directory
|
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that houses all the information about the format and content of the
|
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image data.
|
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Images in a file are usually related but they do not need to be; it
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is perfectly alright to store a color image together with a black and
|
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white image.
|
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Note however that while images may be related their directories are
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not.
|
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That is, each directory stands on its own; their is no need to read
|
|
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an unrelated directory in order to properly interpret the contents
|
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of an image.
|
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|
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<tt>libtiff</tt> provides several routines for reading and writing
|
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directories. In normal use there is no need to explicitly
|
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read or write a directory: the library automatically reads the first
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directory in a file when opened for reading, and directory information
|
|
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to be written is automatically accumulated and written when writing
|
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(assuming <tt>TIFFClose</tt> or <tt>TIFFFlush</tt> are called).
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For a file open for reading the <tt>TIFFSetDirectory</tt> routine can
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be used to select an arbitrary directory; directories are referenced by
|
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number with the numbering starting at 0. Otherwise the
|
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<tt>TIFFReadDirectory</tt> and <tt>TIFFWriteDirectory</tt> routines can
|
|
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be used for sequential access to directories.
|
|
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For example, to count the number of directories in a file the following
|
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code might be used:
|
|
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|
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|
|
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<tt>#include "tiffio.h"
|
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main(int argc, char* argv[])
|
|
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{
|
|
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TIFF* tif = TIFFOpen(argv[1], "r");
|
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if (tif) {
|
|
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int dircount = 0;
|
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do {
|
|
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dircount++;
|
|
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} while (TIFFReadDirectory(tif));
|
|
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printf("%d directories in %s\n", dircount, argv[1]);
|
|
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TIFFClose(tif);
|
|
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}
|
|
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exit(0);
|
|
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}</tt>
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|
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Finally, note that there are several routines for querying the
|
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directory status of an open file:
|
|
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<tt>TIFFCurrentDirectory</tt> returns the index of the current
|
|
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directory and
|
|
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<tt>TIFFLastDirectory</tt> returns an indication of whether the
|
|
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current directory is the last directory in a file.
|
|
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There is also a routine, <tt>TIFFPrintDirectory</tt>, that can
|
|
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be called to print a formatted description of the contents of
|
|
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the current directory; consult the manual page for complete details.
|
|
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|
|
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|
|
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TIFF Tags
|
|
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|
|
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Image-related information such as the image width and height, number
|
|
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of samples, orientation, colorimetric information, etc.
|
|
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are stored in each image
|
|
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directory in fields or tags.
|
|
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Tags are identified by a number that is usually a value registered
|
|
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with the Aldus (now Adobe) Corporation.
|
|
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Beware however that some vendors write
|
|
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TIFF images with tags that are unregistered; in this case interpreting
|
|
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their contents is usually a waste of time.
|
|
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|
|
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|
|
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<tt>libtiff</tt> reads the contents of a directory all at once
|
|
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and converts the on-disk information to an appropriate in-memory
|
|
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form. While the TIFF specification permits an arbitrary set of
|
|
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tags to be defined and used in a file, the library only understands
|
|
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a limited set of tags.
|
|
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Any unknown tags that are encountered in a file are ignored.
|
|
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There is a mechanism to extend the set of tags the library handles
|
|
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without modifying the library itself;
|
|
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this is described elsewhere.
|
|
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|
|
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|
|
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<tt>libtiff</tt> provides two interfaces for getting and setting tag
|
|
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values: <tt>TIFFGetField</tt> and <tt>TIFFSetField</tt>.
|
|
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These routines use a variable argument list-style interface to pass
|
|
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parameters of different type through a single function interface.
|
|
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The get interface takes one or more pointers to memory locations
|
|
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7838c8 |
where the tag values are to be returned and also returns one or
|
|
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7838c8 |
zero according to whether the requested tag is defined in the directory.
|
|
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The set interface takes the tag values either by-reference or
|
|
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by-value.
|
|
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The TIFF specification defines
|
|
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default values for some tags.
|
|
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To get the value of a tag, or its default value if it is undefined,
|
|
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the <tt>TIFFGetFieldDefaulted</tt> interface may be used.
|
|
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|
|
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|
|
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7838c8 |
The manual pages for the tag get and set routines specifiy the exact data types
|
|
Packit |
7838c8 |
and calling conventions required for each tag supported by the library.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
TIFF Compression Schemes
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
<tt>libtiff</tt> includes support for a wide variety of
|
|
Packit |
7838c8 |
data compression schemes.
|
|
Packit |
7838c8 |
In normal operation a compression scheme is automatically used when
|
|
Packit |
7838c8 |
the TIFF <tt>Compression</tt> tag is set, either by opening a file
|
|
Packit |
7838c8 |
for reading, or by setting the tag when writing.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
Compression schemes are implemented by software modules termed codecs
|
|
Packit |
7838c8 |
that implement decoder and encoder routines that hook into the
|
|
Packit |
7838c8 |
core library i/o support.
|
|
Packit |
7838c8 |
Codecs other than those bundled with the library can be registered
|
|
Packit |
7838c8 |
for use with the <tt>TIFFRegisterCODEC</tt> routine.
|
|
Packit |
7838c8 |
This interface can also be used to override the core-library
|
|
Packit |
7838c8 |
implementation for a compression scheme.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
Byte Order
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
The TIFF specification says, and has always said, that
|
|
Packit |
7838c8 |
a correct TIFF
|
|
Packit |
7838c8 |
reader must handle images in big-endian and little-endian byte order.
|
|
Packit |
7838c8 |
<tt>libtiff</tt> conforms in this respect.
|
|
Packit |
7838c8 |
Consequently there is no means to force a specific
|
|
Packit |
7838c8 |
byte order for the data written to a TIFF image file (data is
|
|
Packit |
7838c8 |
written in the native order of the host CPU unless appending to
|
|
Packit |
7838c8 |
an existing file, in which case it is written in the byte order
|
|
Packit |
7838c8 |
specified in the file).
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
Data Placement
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
The TIFF specification requires that all information except an
|
|
Packit |
7838c8 |
8-byte header can be placed anywhere in a file.
|
|
Packit |
7838c8 |
In particular, it is perfectly legitimate for directory information
|
|
Packit |
7838c8 |
to be written after the image data itself.
|
|
Packit |
7838c8 |
Consequently TIFF is inherently not suitable for passing through a
|
|
Packit |
7838c8 |
stream-oriented mechanism such as UNIX pipes.
|
|
Packit |
7838c8 |
Software that require that data be organized in a file in a particular
|
|
Packit |
7838c8 |
order (e.g. directory information before image data) does not
|
|
Packit |
7838c8 |
correctly support TIFF.
|
|
Packit |
7838c8 |
<tt>libtiff</tt> provides no mechanism for controlling the placement
|
|
Packit |
7838c8 |
of data in a file; image data is typically written before directory
|
|
Packit |
7838c8 |
information.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
TIFFRGBAImage Support
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
<tt>libtiff</tt> provides a high-level interface for reading image
|
|
Packit |
7838c8 |
data from a TIFF file. This interface handles the details of
|
|
Packit |
7838c8 |
data organization and format for a wide variety of TIFF files;
|
|
Packit |
7838c8 |
at least the large majority of those files that one would normally
|
|
Packit |
7838c8 |
encounter. Image data is, by default, returned as ABGR
|
|
Packit |
7838c8 |
pixels packed into 32-bit words (8 bits per sample). Rectangular
|
|
Packit |
7838c8 |
rasters can be read or data can be intercepted at an intermediate
|
|
Packit |
7838c8 |
level and packed into memory in a format more suitable to the
|
|
Packit |
7838c8 |
application.
|
|
Packit |
7838c8 |
The library handles all the details of the format of data stored on
|
|
Packit |
7838c8 |
disk and, in most cases, if any colorspace conversions are required:
|
|
Packit |
7838c8 |
bilevel to RGB, greyscale to RGB, CMYK to RGB, YCbCr to RGB, 16-bit
|
|
Packit |
7838c8 |
samples to 8-bit samples, associated/unassociated alpha, etc.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
There are two ways to read image data using this interface. If
|
|
Packit |
7838c8 |
all the data is to be stored in memory and manipulated at once,
|
|
Packit |
7838c8 |
then the routine <tt>TIFFReadRGBAImage</tt> can be used:
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
<tt>#include "tiffio.h"
|
|
Packit |
7838c8 |
main(int argc, char* argv[])
|
|
Packit |
7838c8 |
{
|
|
Packit |
7838c8 |
TIFF* tif = TIFFOpen(argv[1], "r");
|
|
Packit |
7838c8 |
if (tif) {
|
|
Packit |
7838c8 |
uint32 w, h;
|
|
Packit |
7838c8 |
size_t npixels;
|
|
Packit |
7838c8 |
uint32* raster;
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
TIFFGetField(tif, TIFFTAG_IMAGEWIDTH, &w);
|
|
Packit |
7838c8 |
TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &h);
|
|
Packit |
7838c8 |
npixels = w * h;
|
|
Packit |
7838c8 |
raster = (uint32*) _TIFFmalloc(npixels * sizeof (uint32));
|
|
Packit |
7838c8 |
if (raster != NULL) {
|
|
Packit |
7838c8 |
if (TIFFReadRGBAImage(tif, w, h, raster, 0)) {
|
|
Packit |
7838c8 |
...process raster data...
|
|
Packit |
7838c8 |
}
|
|
Packit |
7838c8 |
_TIFFfree(raster);
|
|
Packit |
7838c8 |
}
|
|
Packit |
7838c8 |
TIFFClose(tif);
|
|
Packit |
7838c8 |
}
|
|
Packit |
7838c8 |
exit(0);
|
|
Packit |
7838c8 |
}</tt>
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
Note above that <tt>_TIFFmalloc</tt> is used to allocate memory for
|
|
Packit |
7838c8 |
the raster passed to <tt>TIFFReadRGBAImage</tt>; this is important
|
|
Packit |
7838c8 |
to insure the ``appropriate type of memory'' is passed on machines
|
|
Packit |
7838c8 |
with segmented architectures.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
Alternatively, <tt>TIFFReadRGBAImage</tt> can be replaced with a
|
|
Packit |
7838c8 |
more low-level interface that permits an application to have more
|
|
Packit |
7838c8 |
control over this reading procedure. The equivalent to the above
|
|
Packit |
7838c8 |
is:
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
<tt>#include "tiffio.h"
|
|
Packit |
7838c8 |
main(int argc, char* argv[])
|
|
Packit |
7838c8 |
{
|
|
Packit |
7838c8 |
TIFF* tif = TIFFOpen(argv[1], "r");
|
|
Packit |
7838c8 |
if (tif) {
|
|
Packit |
7838c8 |
TIFFRGBAImage img;
|
|
Packit |
7838c8 |
char emsg[1024];
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
if (TIFFRGBAImageBegin(&img, tif, 0, emsg)) {
|
|
Packit |
7838c8 |
size_t npixels;
|
|
Packit |
7838c8 |
uint32* raster;
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
npixels = img.width * img.height;
|
|
Packit |
7838c8 |
raster = (uint32*) _TIFFmalloc(npixels * sizeof (uint32));
|
|
Packit |
7838c8 |
if (raster != NULL) {
|
|
Packit |
7838c8 |
if (TIFFRGBAImageGet(&img, raster, img.width, img.height)) {
|
|
Packit |
7838c8 |
...process raster data...
|
|
Packit |
7838c8 |
}
|
|
Packit |
7838c8 |
_TIFFfree(raster);
|
|
Packit |
7838c8 |
}
|
|
Packit |
7838c8 |
TIFFRGBAImageEnd(&img);
|
|
Packit |
7838c8 |
} else
|
|
Packit |
7838c8 |
TIFFError(argv[1], emsg);
|
|
Packit |
7838c8 |
TIFFClose(tif);
|
|
Packit |
7838c8 |
}
|
|
Packit |
7838c8 |
exit(0);
|
|
Packit |
7838c8 |
}</tt>
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
However this usage does not take advantage of the more fine-grained
|
|
Packit |
7838c8 |
control that's possible. That is, by using this interface it is
|
|
Packit |
7838c8 |
possible to:
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
repeatedly fetch (and manipulate) an image without opening
|
|
Packit |
7838c8 |
and closing the file
|
|
Packit |
7838c8 |
interpose a method for packing raster pixel data according to
|
|
Packit |
7838c8 |
application-specific needs (or write the data at all)
|
|
Packit |
7838c8 |
interpose methods that handle TIFF formats that are not already
|
|
Packit |
7838c8 |
handled by the core library
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
The first item means that, for example, image viewers that want to
|
|
Packit |
7838c8 |
handle multiple files can cache decoding information in order to
|
|
Packit |
7838c8 |
speedup the work required to display a TIFF image.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
The second item is the main reason for this interface. By interposing
|
|
Packit |
7838c8 |
a "put method" (the routine that is called to pack pixel data in
|
|
Packit |
7838c8 |
the raster) it is possible share the core logic that understands how
|
|
Packit |
7838c8 |
to deal with TIFF while packing the resultant pixels in a format that
|
|
Packit |
7838c8 |
is optimized for the application. This alternate format might be very
|
|
Packit |
7838c8 |
different than the 8-bit per sample ABGR format the library writes by
|
|
Packit |
7838c8 |
default. For example, if the application is going to display the image
|
|
Packit |
7838c8 |
on an 8-bit colormap display the put routine might take the data and
|
|
Packit |
7838c8 |
convert it on-the-fly to the best colormap indices for display.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
The last item permits an application to extend the library
|
|
Packit |
7838c8 |
without modifying the core code.
|
|
Packit |
7838c8 |
By overriding the code provided an application might add support
|
|
Packit |
7838c8 |
for some esoteric flavor of TIFF that it needs, or it might
|
|
Packit |
7838c8 |
substitute a packing routine that is able to do optimizations
|
|
Packit |
7838c8 |
using application/environment-specific information.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
The TIFF image viewer found in tools/sgigt.c is an example
|
|
Packit |
7838c8 |
of an application that makes use of the <tt>TIFFRGBAImage</tt>
|
|
Packit |
7838c8 |
support.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
Scanline-based Image I/O
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
The simplest interface provided by <tt>libtiff</tt> is a
|
|
Packit |
7838c8 |
scanline-oriented interface that can be used to read TIFF
|
|
Packit |
7838c8 |
images that have their image data organized in strips
|
|
Packit |
7838c8 |
(trying to use this interface to read data written in tiles
|
|
Packit |
7838c8 |
will produce errors.)
|
|
Packit |
7838c8 |
A scanline is a one pixel high row of image data whose width
|
|
Packit |
7838c8 |
is the width of the image.
|
|
Packit |
7838c8 |
Data is returned packed if the image data is stored with samples
|
|
Packit |
7838c8 |
packed together, or as arrays of separate samples if the data
|
|
Packit |
7838c8 |
is stored with samples separated.
|
|
Packit |
7838c8 |
The major limitation of the scanline-oriented interface, other
|
|
Packit |
7838c8 |
than the need to first identify an existing file as having a
|
|
Packit |
7838c8 |
suitable organization, is that random access to individual
|
|
Packit |
7838c8 |
scanlines can only be provided when data is not stored in a
|
|
Packit |
7838c8 |
compressed format, or when the number of rows in a strip
|
|
Packit |
7838c8 |
of image data is set to one (<tt>RowsPerStrip</tt> is one).
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
Two routines are provided for scanline-based i/o:
|
|
Packit |
7838c8 |
<tt>TIFFReadScanline</tt>
|
|
Packit |
7838c8 |
and
|
|
Packit |
7838c8 |
<tt>TIFFWriteScanline</tt>.
|
|
Packit |
7838c8 |
For example, to read the contents of a file that
|
|
Packit |
7838c8 |
is assumed to be organized in strips, the following might be used:
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
<tt>#include "tiffio.h"
|
|
Packit |
7838c8 |
main()
|
|
Packit |
7838c8 |
{
|
|
Packit |
7838c8 |
TIFF* tif = TIFFOpen("myfile.tif", "r");
|
|
Packit |
7838c8 |
if (tif) {
|
|
Packit |
7838c8 |
uint32 imagelength;
|
|
Packit |
7838c8 |
tdata_t buf;
|
|
Packit |
7838c8 |
uint32 row;
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imagelength);
|
|
Packit |
7838c8 |
buf = _TIFFmalloc(TIFFScanlineSize(tif));
|
|
Packit |
7838c8 |
for (row = 0; row < imagelength; row++)
|
|
Packit |
7838c8 |
tiffreadscanline(tif, buf, row);
|
|
Packit |
7838c8 |
_tifffree(buf);
|
|
Packit |
7838c8 |
tiffclose(tif);
|
|
Packit |
7838c8 |
}
|
|
Packit |
7838c8 |
}</tt>
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
<tt>TIFFScanlineSize</tt> returns the number of bytes in
|
|
Packit |
7838c8 |
a decoded scanline, as returned by <tt>TIFFReadScanline</tt>.
|
|
Packit |
7838c8 |
Note however that if the file had been create with samples
|
|
Packit |
7838c8 |
written in separate planes, then the above code would only
|
|
Packit |
7838c8 |
read data that contained the first sample of each pixel;
|
|
Packit |
7838c8 |
to handle either case one might use the following instead:
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
<tt>#include "tiffio.h"
|
|
Packit |
7838c8 |
main()
|
|
Packit |
7838c8 |
{
|
|
Packit |
7838c8 |
TIFF* tif = TIFFOpen("myfile.tif", "r");
|
|
Packit |
7838c8 |
if (tif) {
|
|
Packit |
7838c8 |
uint32 imagelength;
|
|
Packit |
7838c8 |
tdata_t buf;
|
|
Packit |
7838c8 |
uint32 row;
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imagelength);
|
|
Packit |
7838c8 |
TIFFGetField(tif, TIFFTAG_PLANARCONFIG, &config);
|
|
Packit |
7838c8 |
buf = _TIFFmalloc(TIFFScanlineSize(tif));
|
|
Packit |
7838c8 |
if (config == PLANARCONFIG_CONTIG) {
|
|
Packit |
7838c8 |
for (row = 0; row < imagelength; row++)
|
|
Packit |
7838c8 |
tiffreadscanline(tif, buf, row);
|
|
Packit |
7838c8 |
} else if (config == planarconfig_separate) {
|
|
Packit |
7838c8 |
uint16 s, nsamples;
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
tiffgetfield(tif, tifftag_samplesperpixel, &nsamples);
|
|
Packit |
7838c8 |
for (s = 0; s < nsamples; s++)
|
|
Packit |
7838c8 |
for (row = 0; row < imagelength; row++)
|
|
Packit |
7838c8 |
tiffreadscanline(tif, buf, row, s);
|
|
Packit |
7838c8 |
}
|
|
Packit |
7838c8 |
_tifffree(buf);
|
|
Packit |
7838c8 |
tiffclose(tif);
|
|
Packit |
7838c8 |
}
|
|
Packit |
7838c8 |
}</tt>
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
Beware however that if the following code were used instead to
|
|
Packit |
7838c8 |
read data in the case <tt>PLANARCONFIG_SEPARATE</tt>,...
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
<tt> for (row = 0; row < imagelength; row++)
|
|
Packit |
7838c8 |
for (s = 0; s < nsamples; s++)
|
|
Packit |
7838c8 |
tiffreadscanline(tif, buf, row, s);</tt>
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
...then problems would arise if <tt>RowsPerStrip</tt> was not one
|
|
Packit |
7838c8 |
because the order in which scanlines are requested would require
|
|
Packit |
7838c8 |
random access to data within strips (something that is not supported
|
|
Packit |
7838c8 |
by the library when strips are compressed).
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
Strip-oriented Image I/O
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
The strip-oriented interfaces provided by the library provide
|
|
Packit |
7838c8 |
access to entire strips of data. Unlike the scanline-oriented
|
|
Packit |
7838c8 |
calls, data can be read or written compressed or uncompressed.
|
|
Packit |
7838c8 |
Accessing data at a strip (or tile) level is often desirable
|
|
Packit |
7838c8 |
because there are no complications with regard to random access
|
|
Packit |
7838c8 |
to data within strips.
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
A simple example of reading an image by strips is:
|
|
Packit |
7838c8 |
|
|
Packit |
7838c8 |
|
|
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<tt>#include "tiffio.h"
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main()
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{
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TIFF* tif = TIFFOpen("myfile.tif", "r");
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if (tif) {
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tdata_t buf;
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tstrip_t strip;
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buf = _TIFFmalloc(TIFFStripSize(tif));
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for (strip = 0; strip < tiffnumberofstrips(tif); strip++)
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tiffreadencodedstrip(tif, strip, buf, (tsize_t) -1);
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_tifffree(buf);
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tiffclose(tif);
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}
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}</tt>
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Notice how a strip size of <tt>-1</tt> is used; <tt>TIFFReadEncodedStrip</tt>
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will calculate the appropriate size in this case.
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The above code reads strips in the order in which the
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data is physically stored in the file. If multiple samples
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are present and data is stored with <tt>PLANARCONFIG_SEPARATE</tt>
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then all the strips of data holding the first sample will be
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read, followed by strips for the second sample, etc.
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Finally, note that the last strip of data in an image may have fewer
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rows in it than specified by the <tt>RowsPerStrip</tt> tag. A
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reader should not assume that each decoded strip contains a full
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set of rows in it.
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The following is an example of how to read raw strips of data from
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a file:
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<tt>#include "tiffio.h"
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main()
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{
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TIFF* tif = TIFFOpen("myfile.tif", "r");
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if (tif) {
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tdata_t buf;
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tstrip_t strip;
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uint32* bc;
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uint32 stripsize;
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TIFFGetField(tif, TIFFTAG_STRIPBYTECOUNTS, &bc);
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stripsize = bc[0];
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buf = _TIFFmalloc(stripsize);
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for (strip = 0; strip < tiffnumberofstrips(tif); strip++) {
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if (bc[strip] > stripsize) {
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buf = _TIFFrealloc(buf, bc[strip]);
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stripsize = bc[strip];
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}
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TIFFReadRawStrip(tif, strip, buf, bc[strip]);
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}
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_TIFFfree(buf);
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TIFFClose(tif);
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}
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}</tt>
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As above the strips are read in the order in which they are
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physically stored in the file; this may be different from the
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logical ordering expected by an application.
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Tile-oriented Image I/O
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Tiles of data may be read and written in a manner similar to strips.
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With this interface, an image is
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broken up into a set of rectangular areas that may have dimensions
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less than the image width and height. All the tiles
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in an image have the same size, and the tile width and length must each
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be a multiple of 16 pixels. Tiles are ordered left-to-right and
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top-to-bottom in an image. As for scanlines, samples can be packed
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contiguously or separately. When separated, all the tiles for a sample
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are colocated in the file. That is, all the tiles for sample 0 appear
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before the tiles for sample 1, etc.
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Tiles and strips may also be extended in a z dimension to form
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volumes. Data volumes are organized as "slices". That is, all the
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data for a slice is colocated. Volumes whose data is organized in
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tiles can also have a tile depth so that data can be organized in
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cubes.
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There are actually two interfaces for tiles.
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One interface is similar to scanlines, to read a tiled image,
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code of the following sort might be used:
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<tt>main()
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{
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TIFF* tif = TIFFOpen("myfile.tif", "r");
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if (tif) {
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uint32 imageWidth, imageLength;
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uint32 tileWidth, tileLength;
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uint32 x, y;
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tdata_t buf;
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TIFFGetField(tif, TIFFTAG_IMAGEWIDTH, &imageWidth);
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TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imageLength);
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TIFFGetField(tif, TIFFTAG_TILEWIDTH, &tileWidth);
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TIFFGetField(tif, TIFFTAG_TILELENGTH, &tileLength);
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buf = _TIFFmalloc(TIFFTileSize(tif));
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for (y = 0; y < imagelength; y += tilelength)
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for (x = 0; x < imagewidth; x += tilewidth)
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tiffreadtile(tif, buf, x, y, 0);
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_tifffree(buf);
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tiffclose(tif);
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}
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}</tt>
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(once again, we assume samples are packed contiguously.)
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Alternatively a direct interface to the low-level data is provided
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a la strips. Tiles can be read with
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<tt>TIFFReadEncodedTile</tt> or <tt>TIFFReadRawTile</tt>,
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and written with <tt>TIFFWriteEncodedTile</tt> or
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<tt>TIFFWriteRawTile</tt>. For example, to read all the tiles in an image:
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<tt>#include "tiffio.h"
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main()
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{
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TIFF* tif = TIFFOpen("myfile.tif", "r");
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if (tif) {
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tdata_t buf;
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ttile_t tile;
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buf = _TIFFmalloc(TIFFTileSize(tif));
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for (tile = 0; tile < tiffnumberoftiles(tif); tile++)
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tiffreadencodedtile(tif, tile, buf, (tsize_t) -1);
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_tifffree(buf);
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tiffclose(tif);
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}
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}</tt>
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Other Stuff
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Some other stuff will almost certainly go here...
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Last updated: $Date: 2016-09-25 20:05:44 $
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</body>
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</html>
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