748 lines
36 KiB
HTML
748 lines
36 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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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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<!--
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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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<table border="0" cellspacing="0" cellpadding="0">
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<tr>
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<td style="padding-left: 1em; padding-right: 1em"><img src="images/cat.gif" width="113" height="146" alt=""></td>
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<td>
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<h1>Using The TIFF Library</h1>
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<p>
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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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</p>
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</td>
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</tr>
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</table>
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<br>
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<p>
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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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</p>
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<p>
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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 <a href="man/index.html">UNIX manual pages</a> that accompany
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this software.
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</p>
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<p>
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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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<a href="http://www.ibm.com/developerworks/linux/library/l-libtiff">http://www.ibm.com/developerworks/linux/library/l-libtiff</a>.
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</p>
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<p>
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The following sections are found in this chapter:
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</p>
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<ul>
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<li><a href="#version">How to tell which version you have</a></li>
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<li><a href="#typedefs">Library Datatypes</a></li>
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<li><a href="#mman">Memory Management</a></li>
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<li><a href="#errors">Error Handling</a></li>
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<li><a href="#fio">Basic File Handling</a></li>
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<li><a href="#dirs">TIFF Directories</a></li>
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<li><a href="#tags">TIFF Tags</a></li>
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<li><a href="#compression">TIFF Compression Schemes</a></li>
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<li><a href="#byteorder">Byte Order</a></li>
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<li><a href="#dataplacement">Data Placement</a></li>
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<li><a href="#tiffrgbaimage">TIFFRGBAImage Support</a></li>
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<li><a href="#scanlines">Scanline-based Image I/O</a></li>
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<li><a href="#strips">Strip-oriented Image I/O</a></li>
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<li><a href="#tiles">Tile-oriented Image I/O</a></li>
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<li><a href="#other">Other Stuff</a></li>
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</ul>
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<hr>
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<h2 id="version">How to tell which version you have</h2>
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<p>
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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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</p>
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<p style="margin-left: 40px">
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<tt>TIFF <<i>version</i>> <<i>alpha</i>></tt>
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</p>
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<p>
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where <tt><<i>version</i>></tt> is whatever you get from
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<tt>"cat VERSION"</tt> and <tt><<i>alpha</i>></tt> is
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what you get from <tt>"cat dist/tiff.alpha"</tt>.
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</p>
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<p>
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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 compatibility at compile time.
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</p>
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<hr>
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<h2 id="typedefs">Library Datatypes</h2>
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<p>
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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 <b>tiff.h</b> and
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<b>tiffio.h</b>,
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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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</p>
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<hr>
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<h2 id="mman">Memory Management</h2>
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<p>
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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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</p>
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<p>
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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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</p>
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<hr>
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<h2 id="errors">Error Handling</h2>
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<p>
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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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</p>
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<hr>
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<h2 id="fio">Basic File Handling</h2>
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<p>
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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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</p>
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<p style="margin-left: 40px">
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<tt>#include "tiffio.h"<br>
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main()<br>
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{<br>
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TIFF* tif = TIFFOpen("foo.tif", "r");<br>
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... do stuff ...<br>
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TIFFClose(tif);<br>
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}</tt>
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</p>
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<p>
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The handle returned by <tt>TIFFOpen</tt> is <i>opaque</i>, 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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</p>
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<p>
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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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<p>
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<p style="margin-left: 40px">
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<tt>#include "tiffio.h"<br>
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main()<br>
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{<br>
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TIFF* tif = TIFFOpen("foo.tif", "w");<br>
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... do stuff ...<br>
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TIFFClose(tif);<br>
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}</tt>
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</p>
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<p>
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If the file already exists it is first truncated to zero length.
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</p>
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<table>
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<tr>
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<td valign=top><img src="images/warning.gif" width="40" height="40" alt=""></td>
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<td><i>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.</i></td>
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</tr>
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</table>
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<p>
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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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</p>
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<hr>
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<h2 id="dirs">TIFF Directories</h2>
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<p>
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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 <i>directory</i>
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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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</p>
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<p>
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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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</p>
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<p>
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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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</p>
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<p style="margin-left: 40px">
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<tt>#include "tiffio.h"<br>
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main(int argc, char* argv[])<br>
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{<br>
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TIFF* tif = TIFFOpen(argv[1], "r");<br>
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if (tif) {<br>
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int dircount = 0;<br>
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do {<br>
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dircount++;<br>
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} while (TIFFReadDirectory(tif));<br>
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printf("%d directories in %s\n", dircount, argv[1]);<br>
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TIFFClose(tif);<br>
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}<br>
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exit(0);<br>
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}</tt>
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</p>
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<p>
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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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</p>
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<hr>
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<h2 id="tags">TIFF Tags</h2>
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<p>
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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 <i>fields</i> or <i>tags</i>.
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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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</p>
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<p>
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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 <a href="addingtags.html">elsewhere</a>.
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</p>
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<p>
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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 <i>get interface</i> takes one or more pointers to memory locations
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where the tag values are to be returned and also returns one or
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zero according to whether the requested tag is defined in the directory.
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The <i>set interface</i> 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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<i>default values</i> 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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</p>
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<p>
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The manual pages for the tag get and set routines specifiy the exact data types
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and calling conventions required for each tag supported by the library.
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</p>
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<hr>
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<h2 id="compression">TIFF Compression Schemes</h2>
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<p>
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<tt>libtiff</tt> includes support for a wide variety of
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data compression schemes.
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In normal operation a compression scheme is automatically used when
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the TIFF <tt>Compression</tt> tag is set, either by opening a file
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for reading, or by setting the tag when writing.
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</p>
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<p>
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Compression schemes are implemented by software modules termed <i>codecs</i>
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that implement decoder and encoder routines that hook into the
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core library i/o support.
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Codecs other than those bundled with the library can be registered
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for use with the <tt>TIFFRegisterCODEC</tt> routine.
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This interface can also be used to override the core-library
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implementation for a compression scheme.
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</p>
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<hr>
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<h2 id="byteorder">Byte Order</h2>
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<p>
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The TIFF specification says, and has always said, that
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<em>a correct TIFF
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reader must handle images in big-endian and little-endian byte order</em>.
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<tt>libtiff</tt> conforms in this respect.
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Consequently there is no means to force a specific
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byte order for the data written to a TIFF image file (data is
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written in the native order of the host CPU unless appending to
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an existing file, in which case it is written in the byte order
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specified in the file).
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</p>
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<hr>
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<h2 id="dataplacement">Data Placement</h2>
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<p>
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The TIFF specification requires that all information except an
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8-byte header can be placed anywhere in a file.
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In particular, it is perfectly legitimate for directory information
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to be written after the image data itself.
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Consequently TIFF is inherently not suitable for passing through a
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stream-oriented mechanism such as UNIX pipes.
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Software that require that data be organized in a file in a particular
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order (e.g. directory information before image data) does not
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correctly support TIFF.
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<tt>libtiff</tt> provides no mechanism for controlling the placement
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of data in a file; image data is typically written before directory
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information.
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</p>
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<hr>
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<h2 id="tiffrgbaimage">TIFFRGBAImage Support</h2>
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<p>
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<tt>libtiff</tt> provides a high-level interface for reading image
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data from a TIFF file. This interface handles the details of
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data organization and format for a wide variety of TIFF files;
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at least the large majority of those files that one would normally
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encounter. Image data is, by default, returned as ABGR
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pixels packed into 32-bit words (8 bits per sample). Rectangular
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rasters can be read or data can be intercepted at an intermediate
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level and packed into memory in a format more suitable to the
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application.
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The library handles all the details of the format of data stored on
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disk and, in most cases, if any colorspace conversions are required:
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bilevel to RGB, greyscale to RGB, CMYK to RGB, YCbCr to RGB, 16-bit
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samples to 8-bit samples, associated/unassociated alpha, etc.
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</p>
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<p>
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There are two ways to read image data using this interface. If
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all the data is to be stored in memory and manipulated at once,
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then the routine <tt>TIFFReadRGBAImage</tt> can be used:
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</p>
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<p>
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<p style="margin-left: 40px">
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<tt>#include "tiffio.h"<br>
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main(int argc, char* argv[])<br>
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{<br>
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TIFF* tif = TIFFOpen(argv[1], "r");<br>
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if (tif) {<br>
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uint32 w, h;<br>
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size_t npixels;<br>
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uint32* raster;<br>
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<br>
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TIFFGetField(tif, TIFFTAG_IMAGEWIDTH, &w);<br>
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TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &h);<br>
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npixels = w * h;<br>
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raster = (uint32*) _TIFFmalloc(npixels * sizeof (uint32));<br>
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if (raster != NULL) {<br>
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if (TIFFReadRGBAImage(tif, w, h, raster, 0)) {<br>
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...process raster data...<br>
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}<br>
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_TIFFfree(raster);<br>
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}<br>
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TIFFClose(tif);<br>
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}<br>
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exit(0);<br>
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}</tt>
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</p>
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<p>
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Note above that <tt>_TIFFmalloc</tt> is used to allocate memory for
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the raster passed to <tt>TIFFReadRGBAImage</tt>; this is important
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to insure the ``appropriate type of memory'' is passed on machines
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with segmented architectures.
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</p>
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<p>
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Alternatively, <tt>TIFFReadRGBAImage</tt> can be replaced with a
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more low-level interface that permits an application to have more
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control over this reading procedure. The equivalent to the above
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is:
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</p>
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<p style="margin-left: 40px">
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<tt>#include "tiffio.h"<br>
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main(int argc, char* argv[])<br>
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{<br>
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TIFF* tif = TIFFOpen(argv[1], "r");<br>
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if (tif) {<br>
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TIFFRGBAImage img;<br>
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char emsg[1024];<br>
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<br>
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if (TIFFRGBAImageBegin(&img, tif, 0, emsg)) {<br>
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size_t npixels;<br>
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uint32* raster;<br>
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<br>
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npixels = img.width * img.height;<br>
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raster = (uint32*) _TIFFmalloc(npixels * sizeof (uint32));<br>
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if (raster != NULL) {<br>
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if (TIFFRGBAImageGet(&img, raster, img.width, img.height)) {<br>
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...process raster data...<br>
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}<br>
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_TIFFfree(raster);<br>
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}<br>
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TIFFRGBAImageEnd(&img);<br>
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} else<br>
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TIFFError(argv[1], emsg);<br>
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TIFFClose(tif);<br>
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}<br>
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exit(0);<br>
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}</tt>
|
|
</p>
|
|
<p>
|
|
However this usage does not take advantage of the more fine-grained
|
|
control that's possible. That is, by using this interface it is
|
|
possible to:
|
|
</p>
|
|
<ul>
|
|
<li>repeatedly fetch (and manipulate) an image without opening
|
|
and closing the file</li>
|
|
<li>interpose a method for packing raster pixel data according to
|
|
application-specific needs (or write the data at all)</li>
|
|
<li>interpose methods that handle TIFF formats that are not already
|
|
handled by the core library</li>
|
|
</ul>
|
|
<p>
|
|
The first item means that, for example, image viewers that want to
|
|
handle multiple files can cache decoding information in order to
|
|
speedup the work required to display a TIFF image.
|
|
</p>
|
|
<p>
|
|
The second item is the main reason for this interface. By interposing
|
|
a "put method" (the routine that is called to pack pixel data in
|
|
the raster) it is possible share the core logic that understands how
|
|
to deal with TIFF while packing the resultant pixels in a format that
|
|
is optimized for the application. This alternate format might be very
|
|
different than the 8-bit per sample ABGR format the library writes by
|
|
default. For example, if the application is going to display the image
|
|
on an 8-bit colormap display the put routine might take the data and
|
|
convert it on-the-fly to the best colormap indices for display.
|
|
</p>
|
|
<p>
|
|
The last item permits an application to extend the library
|
|
without modifying the core code.
|
|
By overriding the code provided an application might add support
|
|
for some esoteric flavor of TIFF that it needs, or it might
|
|
substitute a packing routine that is able to do optimizations
|
|
using application/environment-specific information.
|
|
</p>
|
|
<p>
|
|
The TIFF image viewer found in <b>tools/sgigt.c</b> is an example
|
|
of an application that makes use of the <tt>TIFFRGBAImage</tt>
|
|
support.
|
|
</p>
|
|
<hr>
|
|
<h2 id="scanlines">Scanline-based Image I/O</h2>
|
|
<p>
|
|
The simplest interface provided by <tt>libtiff</tt> is a
|
|
scanline-oriented interface that can be used to read TIFF
|
|
images that have their image data organized in strips
|
|
(trying to use this interface to read data written in tiles
|
|
will produce errors.)
|
|
A scanline is a one pixel high row of image data whose width
|
|
is the width of the image.
|
|
Data is returned packed if the image data is stored with samples
|
|
packed together, or as arrays of separate samples if the data
|
|
is stored with samples separated.
|
|
The major limitation of the scanline-oriented interface, other
|
|
than the need to first identify an existing file as having a
|
|
suitable organization, is that random access to individual
|
|
scanlines can only be provided when data is not stored in a
|
|
compressed format, or when the number of rows in a strip
|
|
of image data is set to one (<tt>RowsPerStrip</tt> is one).
|
|
</p>
|
|
<p>
|
|
Two routines are provided for scanline-based i/o:
|
|
<tt>TIFFReadScanline</tt>
|
|
and
|
|
<tt>TIFFWriteScanline</tt>.
|
|
For example, to read the contents of a file that
|
|
is assumed to be organized in strips, the following might be used:
|
|
</p>
|
|
<p style="margin-left: 40px">
|
|
<tt>#include "tiffio.h"<br>
|
|
main()<br>
|
|
{<br>
|
|
TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
|
|
if (tif) {<br>
|
|
uint32 imagelength;<br>
|
|
tdata_t buf;<br>
|
|
uint32 row;<br>
|
|
<br>
|
|
TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imagelength);<br>
|
|
buf = _TIFFmalloc(TIFFScanlineSize(tif));<br>
|
|
for (row = 0; row < imagelength; row++)<br>
|
|
tiffreadscanline(tif, buf, row);<br>
|
|
_tifffree(buf);<br>
|
|
tiffclose(tif);<br>
|
|
}<br>
|
|
}</tt>
|
|
</p>
|
|
<p>
|
|
<tt>TIFFScanlineSize</tt> returns the number of bytes in
|
|
a decoded scanline, as returned by <tt>TIFFReadScanline</tt>.
|
|
Note however that if the file had been create with samples
|
|
written in separate planes, then the above code would only
|
|
read data that contained the first sample of each pixel;
|
|
to handle either case one might use the following instead:
|
|
</p>
|
|
<p style="margin-left: 40px">
|
|
<tt>#include "tiffio.h"<br>
|
|
main()<br>
|
|
{<br>
|
|
TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
|
|
if (tif) {<br>
|
|
uint32 imagelength;<br>
|
|
tdata_t buf;<br>
|
|
uint32 row;<br>
|
|
<br>
|
|
TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imagelength);<br>
|
|
TIFFGetField(tif, TIFFTAG_PLANARCONFIG, &config);<br>
|
|
buf = _TIFFmalloc(TIFFScanlineSize(tif));<br>
|
|
if (config == PLANARCONFIG_CONTIG) {<br>
|
|
for (row = 0; row < imagelength; row++)<br>
|
|
tiffreadscanline(tif, buf, row);<br>
|
|
} else if (config == planarconfig_separate) {<br>
|
|
uint16 s, nsamples;<br>
|
|
<br>
|
|
tiffgetfield(tif, tifftag_samplesperpixel, &nsamples);<br>
|
|
for (s = 0; s < nsamples; s++)<br>
|
|
for (row = 0; row < imagelength; row++)<br>
|
|
tiffreadscanline(tif, buf, row, s);<br>
|
|
}<br>
|
|
_tifffree(buf);<br>
|
|
tiffclose(tif);<br>
|
|
}<br>
|
|
}</tt>
|
|
</p>
|
|
<p>
|
|
Beware however that if the following code were used instead to
|
|
read data in the case <tt>PLANARCONFIG_SEPARATE</tt>,...
|
|
</p>
|
|
<p style="margin-left: 40px">
|
|
<tt> for (row = 0; row < imagelength; row++)<br>
|
|
for (s = 0; s < nsamples; s++)<br>
|
|
tiffreadscanline(tif, buf, row, s);</tt>
|
|
</p>
|
|
<p>
|
|
...then problems would arise if <tt>RowsPerStrip</tt> was not one
|
|
because the order in which scanlines are requested would require
|
|
random access to data within strips (something that is not supported
|
|
by the library when strips are compressed).
|
|
</p>
|
|
<hr>
|
|
<h2 id="strips">Strip-oriented Image I/O</h2>
|
|
<p>
|
|
The strip-oriented interfaces provided by the library provide
|
|
access to entire strips of data. Unlike the scanline-oriented
|
|
calls, data can be read or written compressed or uncompressed.
|
|
Accessing data at a strip (or tile) level is often desirable
|
|
because there are no complications with regard to random access
|
|
to data within strips.
|
|
</p>
|
|
<p>
|
|
A simple example of reading an image by strips is:
|
|
</p>
|
|
<p style="margin-left: 40px">
|
|
<tt>#include "tiffio.h"<br>
|
|
main()<br>
|
|
{<br>
|
|
TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
|
|
if (tif) {<br>
|
|
tdata_t buf;<br>
|
|
tstrip_t strip;<br>
|
|
<br>
|
|
buf = _TIFFmalloc(TIFFStripSize(tif));<br>
|
|
for (strip = 0; strip < tiffnumberofstrips(tif); strip++)<br>
|
|
tiffreadencodedstrip(tif, strip, buf, (tsize_t) -1);<br>
|
|
_tifffree(buf);<br>
|
|
tiffclose(tif);<br>
|
|
}<br>
|
|
}</tt>
|
|
</p>
|
|
<p>
|
|
Notice how a strip size of <tt>-1</tt> is used; <tt>TIFFReadEncodedStrip</tt>
|
|
will calculate the appropriate size in this case.
|
|
</p>
|
|
<p>
|
|
The above code reads strips in the order in which the
|
|
data is physically stored in the file. If multiple samples
|
|
are present and data is stored with <tt>PLANARCONFIG_SEPARATE</tt>
|
|
then all the strips of data holding the first sample will be
|
|
read, followed by strips for the second sample, etc.
|
|
</p>
|
|
<p>
|
|
Finally, note that the last strip of data in an image may have fewer
|
|
rows in it than specified by the <tt>RowsPerStrip</tt> tag. A
|
|
reader should not assume that each decoded strip contains a full
|
|
set of rows in it.
|
|
</p>
|
|
<p>
|
|
The following is an example of how to read raw strips of data from
|
|
a file:
|
|
</p>
|
|
<p style="margin-left: 40px">
|
|
<tt>#include "tiffio.h"<br>
|
|
main()<br>
|
|
{<br>
|
|
TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
|
|
if (tif) {<br>
|
|
tdata_t buf;<br>
|
|
tstrip_t strip;<br>
|
|
uint32* bc;<br>
|
|
uint32 stripsize;<br>
|
|
<br>
|
|
TIFFGetField(tif, TIFFTAG_STRIPBYTECOUNTS, &bc);<br>
|
|
stripsize = bc[0];<br>
|
|
buf = _TIFFmalloc(stripsize);<br>
|
|
for (strip = 0; strip < tiffnumberofstrips(tif); strip++) {<br>
|
|
if (bc[strip] > stripsize) {<br>
|
|
buf = _TIFFrealloc(buf, bc[strip]);<br>
|
|
stripsize = bc[strip];<br>
|
|
}<br>
|
|
TIFFReadRawStrip(tif, strip, buf, bc[strip]);<br>
|
|
}<br>
|
|
_TIFFfree(buf);<br>
|
|
TIFFClose(tif);<br>
|
|
}<br>
|
|
}</tt>
|
|
</p>
|
|
<p>
|
|
As above the strips are read in the order in which they are
|
|
physically stored in the file; this may be different from the
|
|
logical ordering expected by an application.
|
|
</p>
|
|
<hr>
|
|
<h2 id="tiles">Tile-oriented Image I/O</h2>
|
|
<p>
|
|
Tiles of data may be read and written in a manner similar to strips.
|
|
With this interface, an image is
|
|
broken up into a set of rectangular areas that may have dimensions
|
|
less than the image width and height. All the tiles
|
|
in an image have the same size, and the tile width and length must each
|
|
be a multiple of 16 pixels. Tiles are ordered left-to-right and
|
|
top-to-bottom in an image. As for scanlines, samples can be packed
|
|
contiguously or separately. When separated, all the tiles for a sample
|
|
are colocated in the file. That is, all the tiles for sample 0 appear
|
|
before the tiles for sample 1, etc.
|
|
</p>
|
|
<p>
|
|
Tiles and strips may also be extended in a z dimension to form
|
|
volumes. Data volumes are organized as "slices". That is, all the
|
|
data for a slice is colocated. Volumes whose data is organized in
|
|
tiles can also have a tile depth so that data can be organized in
|
|
cubes.
|
|
</p>
|
|
<p>
|
|
There are actually two interfaces for tiles.
|
|
One interface is similar to scanlines, to read a tiled image,
|
|
code of the following sort might be used:
|
|
</p>
|
|
<p style="margin-left: 40px">
|
|
<tt>main()<br>
|
|
{<br>
|
|
TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
|
|
if (tif) {<br>
|
|
uint32 imageWidth, imageLength;<br>
|
|
uint32 tileWidth, tileLength;<br>
|
|
uint32 x, y;<br>
|
|
tdata_t buf;<br>
|
|
<br>
|
|
TIFFGetField(tif, TIFFTAG_IMAGEWIDTH, &imageWidth);<br>
|
|
TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imageLength);<br>
|
|
TIFFGetField(tif, TIFFTAG_TILEWIDTH, &tileWidth);<br>
|
|
TIFFGetField(tif, TIFFTAG_TILELENGTH, &tileLength);<br>
|
|
buf = _TIFFmalloc(TIFFTileSize(tif));<br>
|
|
for (y = 0; y < imagelength; y += tilelength)<br>
|
|
for (x = 0; x < imagewidth; x += tilewidth)<br>
|
|
tiffreadtile(tif, buf, x, y, 0);<br>
|
|
_tifffree(buf);<br>
|
|
tiffclose(tif);<br>
|
|
}<br>
|
|
}</tt>
|
|
</p>
|
|
<p>
|
|
(once again, we assume samples are packed contiguously.)
|
|
</p>
|
|
<p>
|
|
Alternatively a direct interface to the low-level data is provided
|
|
a la strips. Tiles can be read with
|
|
<tt>TIFFReadEncodedTile</tt> or <tt>TIFFReadRawTile</tt>,
|
|
and written with <tt>TIFFWriteEncodedTile</tt> or
|
|
<tt>TIFFWriteRawTile</tt>. For example, to read all the tiles in an image:
|
|
</p>
|
|
<p style="margin-left: 40px">
|
|
<tt>#include "tiffio.h"<br>
|
|
main()<br>
|
|
{<br>
|
|
TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
|
|
if (tif) {<br>
|
|
tdata_t buf;<br>
|
|
ttile_t tile;<br>
|
|
<br>
|
|
buf = _TIFFmalloc(TIFFTileSize(tif));<br>
|
|
for (tile = 0; tile < tiffnumberoftiles(tif); tile++)<br>
|
|
tiffreadencodedtile(tif, tile, buf, (tsize_t) -1);<br>
|
|
_tifffree(buf);<br>
|
|
tiffclose(tif);<br>
|
|
}<br>
|
|
}</tt>
|
|
</p>
|
|
<hr>
|
|
<h2 id="other">Other Stuff</h2>
|
|
<p>
|
|
Some other stuff will almost certainly go here...
|
|
</p>
|
|
<hr>
|
|
<p>
|
|
Last updated: $Date: 2016-09-25 20:05:44 $
|
|
</p>
|
|
</body>
|
|
</html>
|