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1	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
2	<html lang="en">
3	<head>
4	<title>Using The TIFF Library</title>
5	<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
6	<meta http-equiv="content-language" content="en">
7	<style type="text/css">
8	<!--
9	th {text-align: left; vertical-align: top; font-style: italic; font-weight: normal}
10	-->
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12	</head>
13	<body lang="en" text="#000000" bgcolor="#ffffff" link="#0000ff" alink="#0000ff" vlink="#0000ff">
14	<table border="0" cellspacing="0" cellpadding="0">
15	<tr>
16	<td style="padding-left: 1em; padding-right: 1em"><img src="images/cat.gif" width="113" height="146" alt=""></td>
17	<td>
18	<h1>Using The TIFF Library</h1>
19	<p>
20	<tt>libtiff</tt> is a set of C functions (a library) that support
21	the manipulation of TIFF image files.
22	The library requires an ANSI C compilation environment for building
23	and presumes an ANSI C environment for use.
24	</p>
25	</td>
26	</tr>
27	</table>
28	<br>
29	<p>
30	<tt>libtiff</tt>
31	provides interfaces to image data at several layers of abstraction (and cost).
32	At the highest level image data can be read into an 8-bit/sample,
33	ABGR pixel raster format without regard for the underlying data organization,
34	colorspace, or compression scheme. Below this high-level interface
35	the library provides scanline-, strip-, and tile-oriented interfaces that
36	return data decompressed but otherwise untransformed. These interfaces
37	require that the application first identify the organization of stored
38	data and select either a strip-based or tile-based API for manipulating
39	data. At the lowest level the library
40	provides access to the raw uncompressed strips or tiles,
41	returning the data exactly as it appears in the file.
42	</p>
43	<p>
44	The material presented in this chapter is a basic introduction
45	to the capabilities of the library; it is not an attempt to describe
46	everything a developer needs to know about the library or about TIFF.
47	Detailed information on the interfaces to the library are given in
48	the <a href="http://www.remotesensing.org/libtiff/man/index.html">UNIX
49	manual pages</a> that accompany this software.
50	</p>
51	<p>
52	Michael Still has also written a useful introduction to libtiff for the
53	IBM DeveloperWorks site available at
54	<a href="http://www.ibm.com/developerworks/linux/library/l-libtiff">http://www.ibm.com/developerworks/linux/library/l-libtiff</a>.
55	</p>
56	<p>
57	The following sections are found in this chapter:
58	</p>
59	<ul>
60	<li><a href="#version">How to tell which version you have</a></li>
61	<li><a href="#typedefs">Library Datatypes</a></li>
62	<li><a href="#mman">Memory Management</a></li>
63	<li><a href="#errors">Error Handling</a></li>
64	<li><a href="#fio">Basic File Handling</a></li>
65	<li><a href="#dirs">TIFF Directories</a></li>
66	<li><a href="#tags">TIFF Tags</a></li>
67	<li><a href="#compression">TIFF Compression Schemes</a></li>
68	<li><a href="#byteorder">Byte Order</a></li>
69	<li><a href="#dataplacement">Data Placement</a></li>
70	<li><a href="#tiffrgbaimage">TIFFRGBAImage Support</a></li>
71	<li><a href="#scanlines">Scanline-based Image I/O</a></li>
72	<li><a href="#strips">Strip-oriented Image I/O</a></li>
73	<li><a href="#tiles">Tile-oriented Image I/O</a></li>
74	<li><a href="#other">Other Stuff</a></li>
75	</ul>
76	<hr>
77	<h2 id="version">How to tell which version you have</h2>
78	<p>
79	The software version can be found by looking at the file named
80	<tt>VERSION</tt>
81	that is located at the top of the source tree; the precise alpha number
82	is given in the file <tt>dist/tiff.alpha</tt>.
83	If you have need to refer to this
84	specific software, you should identify it as:
85	</p>
86	<p style="margin-left: 40px">
87	<tt>TIFF <<i>version</i>> <<i>alpha</i>></tt>
88	</p>
89	<p>
90	where <tt><<i>version</i>></tt> is whatever you get from
91	<tt>"cat VERSION"</tt> and <tt><<i>alpha</i>></tt> is
92	what you get from <tt>"cat dist/tiff.alpha"</tt>.
93	</p>
94	<p>
95	Within an application that uses <tt>libtiff</tt> the <tt>TIFFGetVersion</tt>
96	routine will return a pointer to a string that contains software version
97	information.
98	The library include file <tt><tiffio.h></tt> contains a C pre-processor
99	define <tt>TIFFLIB_VERSION</tt> that can be used to check library
100	version compatiblity at compile time.
101	</p>
102	<hr>
103	<h2 id="typedefs">Library Datatypes</h2>
104	<p>
105	<tt>libtiff</tt> defines a portable programming interface through the
106	use of a set of C type definitions.
107	These definitions, defined in in the files <b>tiff.h</b> and
108	<b>tiffio.h</b>,
109	isolate the <tt>libtiff</tt> API from the characteristics
110	of the underlying machine.
111	To insure portable code and correct operation, applications that use
112	<tt>libtiff</tt> should use the typedefs and follow the function
113	prototypes for the library API.
114	</p>
115	<hr>
116	<h2 id="mman">Memory Management</h2>
117	<p>
118	<tt>libtiff</tt> uses a machine-specific set of routines for managing
119	dynamically allocated memory.
120	<tt>_TIFFmalloc</tt>, <tt>_TIFFrealloc</tt>, and <tt>_TIFFfree</tt>
121	mimic the normal ANSI C routines.
122	Any dynamically allocated memory that is to be passed into the library
123	should be allocated using these interfaces in order to insure pointer
124	compatibility on machines with a segmented architecture.
125	(On 32-bit UNIX systems these routines just call the normal <tt>malloc</tt>,
126	<tt>realloc</tt>, and <tt>free</tt> routines in the C library.)
127	</p>
128	<p>
129	To deal with segmented pointer issues <tt>libtiff</tt> also provides
130	<tt>_TIFFmemcpy</tt>, <tt>_TIFFmemset</tt>, and <tt>_TIFFmemmove</tt>
131	routines that mimic the equivalent ANSI C routines, but that are
132	intended for use with memory allocated through <tt>_TIFFmalloc</tt>
133	and <tt>_TIFFrealloc</tt>.
134	</p>
135	<hr>
136	<h2 id="errors">Error Handling</h2>
137	<p>
138	<tt>libtiff</tt> handles most errors by returning an invalid/erroneous
139	value when returning from a function call.
140	Various diagnostic messages may also be generated by the library.
141	All error messages are directed to a single global error handler
142	routine that can be specified with a call to <tt>TIFFSetErrorHandler</tt>.
143	Likewise warning messages are directed to a single handler routine
144	that can be specified with a call to <tt>TIFFSetWarningHandler</tt>
145	</p>
146	<hr>
147	<h2 id="fio">Basic File Handling</h2>
148	<p>
149	The library is modeled after the normal UNIX stdio library.
150	For example, to read from an existing TIFF image the
151	file must first be opened:
152	</p>
153	<p style="margin-left: 40px">
154	<tt>#include "tiffio.h"<br>
155	main()<br>
156	{<br>
157	TIFF* tif = TIFFOpen("foo.tif", "r");<br>
158	... do stuff ...<br>
159	TIFFClose(tif);<br>
160	}</tt>
161	</p>
162	<p>
163	The handle returned by <tt>TIFFOpen</tt> is <i>opaque</i>, that is
164	the application is not permitted to know about its contents.
165	All subsequent library calls for this file must pass the handle
166	as an argument.
167	</p>
168	<p>
169	To create or overwrite a TIFF image the file is also opened, but with
170	a <tt>"w"</tt> argument:
171	<p>
172	<p style="margin-left: 40px">
173	<tt>#include "tiffio.h"<br>
174	main()<br>
175	{<br>
176	TIFF* tif = TIFFOpen("foo.tif", "w");<br>
177	... do stuff ...<br>
178	TIFFClose(tif);<br>
179	}</tt>
180	</p>
181	<p>
182	If the file already exists it is first truncated to zero length.
183	</p>
184	<table>
185	<tr>
186	<td valign=top><img src="images/warning.gif" width="40" height="40" alt=""></td>
187	<td><i>Note that unlike the stdio library TIFF image files may not be
188	opened for both reading and writing;
189	there is no support for altering the contents of a TIFF file.</i></td>
190	</tr>
191	</table>
192	<p>
193	<tt>libtiff</tt> buffers much information associated with writing a
194	valid TIFF image. Consequently, when writing a TIFF image it is necessary
195	to always call <tt>TIFFClose</tt> or <tt>TIFFFlush</tt> to flush any
196	buffered information to a file. Note that if you call <tt>TIFFClose</tt>
197	you do not need to call <tt>TIFFFlush</tt>.
198	</p>
199	<hr>
200	<h2 id="dirs">TIFF Directories</h2>
201	<p>
202	TIFF supports the storage of multiple images in a single file.
203	Each image has an associated data structure termed a <i>directory</i>
204	that houses all the information about the format and content of the
205	image data.
206	Images in a file are usually related but they do not need to be; it
207	is perfectly alright to store a color image together with a black and
208	white image.
209	Note however that while images may be related their directories are
210	not.
211	That is, each directory stands on its own; their is no need to read
212	an unrelated directory in order to properly interpret the contents
213	of an image.
214	</p>
215	<p>
216	<tt>libtiff</tt> provides several routines for reading and writing
217	directories. In normal use there is no need to explicitly
218	read or write a directory: the library automatically reads the first
219	directory in a file when opened for reading, and directory information
220	to be written is automatically accumulated and written when writing
221	(assuming <tt>TIFFClose</tt> or <tt>TIFFFlush</tt> are called).
222	</p>
223	<p>
224	For a file open for reading the <tt>TIFFSetDirectory</tt> routine can
225	be used to select an arbitrary directory; directories are referenced by
226	number with the numbering starting at 0. Otherwise the
227	<tt>TIFFReadDirectory</tt> and <tt>TIFFWriteDirectory</tt> routines can
228	be used for sequential access to directories.
229	For example, to count the number of directories in a file the following
230	code might be used:
231	</p>
232	<p style="margin-left: 40px">
233	<tt>#include "tiffio.h"<br>
234	main(int argc, char* argv[])<br>
235	{<br>
236	TIFF* tif = TIFFOpen(argv[1], "r");<br>
237	if (tif) {<br>
238	int dircount = 0;<br>
239	do {<br>
240	dircount++;<br>
241	} while (TIFFReadDirectory(tif));<br>
242	printf("%d directories in %s\n", dircount, argv[1]);<br>
243	TIFFClose(tif);<br>
244	}<br>
245	exit(0);<br>
246	}</tt>
247	</p>
248	<p>
249	Finally, note that there are several routines for querying the
250	directory status of an open file:
251	<tt>TIFFCurrentDirectory</tt> returns the index of the current
252	directory and
253	<tt>TIFFLastDirectory</tt> returns an indication of whether the
254	current directory is the last directory in a file.
255	There is also a routine, <tt>TIFFPrintDirectory</tt>, that can
256	be called to print a formatted description of the contents of
257	the current directory; consult the manual page for complete details.
258	</p>
259	<hr>
260	<h2 id="tags">TIFF Tags</h2>
261	<p>
262	Image-related information such as the image width and height, number
263	of samples, orientation, colorimetric information, etc.
264	are stored in each image
265	directory in <i>fields</i> or <i>tags</i>.
266	Tags are identified by a number that is usually a value registered
267	with the Aldus (now Adobe) Corporation.
268	Beware however that some vendors write
269	TIFF images with tags that are unregistered; in this case interpreting
270	their contents is usually a waste of time.
271	</p>
272	<p>
273	<tt>libtiff</tt> reads the contents of a directory all at once
274	and converts the on-disk information to an appropriate in-memory
275	form. While the TIFF specification permits an arbitrary set of
276	tags to be defined and used in a file, the library only understands
277	a limited set of tags.
278	Any unknown tags that are encountered in a file are ignored.
279	There is a mechanism to extend the set of tags the library handles
280	without modifying the library itself;
281	this is described <a href="addingtags.html">elsewhere</a>.
282	</p>
283	<p>
284	<tt>libtiff</tt> provides two interfaces for getting and setting tag
285	values: <tt>TIFFGetField</tt> and <tt>TIFFSetField</tt>.
286	These routines use a variable argument list-style interface to pass
287	parameters of different type through a single function interface.
288	The <i>get interface</i> takes one or more pointers to memory locations
289	where the tag values are to be returned and also returns one or
290	zero according to whether the requested tag is defined in the directory.
291	The <i>set interface</i> takes the tag values either by-reference or
292	by-value.
293	The TIFF specification defines
294	<i>default values</i> for some tags.
295	To get the value of a tag, or its default value if it is undefined,
296	the <tt>TIFFGetFieldDefaulted</tt> interface may be used.
297	</p>
298	<p>
299	The manual pages for the tag get and set routines specifiy the exact data types
300	and calling conventions required for each tag supported by the library.
301	</p>
302	<hr>
303	<h2 id="compression">TIFF Compression Schemes</h2>
304	<p>
305	<tt>libtiff</tt> includes support for a wide variety of
306	data compression schemes.
307	In normal operation a compression scheme is automatically used when
308	the TIFF <tt>Compression</tt> tag is set, either by opening a file
309	for reading, or by setting the tag when writing.
310	</p>
311	<p>
312	Compression schemes are implemented by software modules termed <i>codecs</i>
313	that implement decoder and encoder routines that hook into the
314	core library i/o support.
315	Codecs other than those bundled with the library can be registered
316	for use with the <tt>TIFFRegisterCODEC</tt> routine.
317	This interface can also be used to override the core-library
318	implementation for a compression scheme.
319	</p>
320	<hr>
321	<h2 id="byteorder">Byte Order</h2>
322	<p>
323	The TIFF specification says, and has always said, that
324	<em>a correct TIFF
325	reader must handle images in big-endian and little-endian byte order</em>.
326	<tt>libtiff</tt> conforms in this respect.
327	Consequently there is no means to force a specific
328	byte order for the data written to a TIFF image file (data is
329	written in the native order of the host CPU unless appending to
330	an existing file, in which case it is written in the byte order
331	specified in the file).
332	</p>
333	<hr>
334	<h2 id="dataplacement">Data Placement</h2>
335	<p>
336	The TIFF specification requires that all information except an
337	8-byte header can be placed anywhere in a file.
338	In particular, it is perfectly legitimate for directory information
339	to be written after the image data itself.
340	Consequently TIFF is inherently not suitable for passing through a
341	stream-oriented mechanism such as UNIX pipes.
342	Software that require that data be organized in a file in a particular
343	order (e.g. directory information before image data) does not
344	correctly support TIFF.
345	<tt>libtiff</tt> provides no mechanism for controlling the placement
346	of data in a file; image data is typically written before directory
347	information.
348	</p>
349	<hr>
350	<h2 id="tiffrgbaimage">TIFFRGBAImage Support</h2>
351	<p>
352	<tt>libtiff</tt> provides a high-level interface for reading image
353	data from a TIFF file. This interface handles the details of
354	data organization and format for a wide variety of TIFF files;
355	at least the large majority of those files that one would normally
356	encounter. Image data is, by default, returned as ABGR
357	pixels packed into 32-bit words (8 bits per sample). Rectangular
358	rasters can be read or data can be intercepted at an intermediate
359	level and packed into memory in a format more suitable to the
360	application.
361	The library handles all the details of the format of data stored on
362	disk and, in most cases, if any colorspace conversions are required:
363	bilevel to RGB, greyscale to RGB, CMYK to RGB, YCbCr to RGB, 16-bit
364	samples to 8-bit samples, associated/unassociated alpha, etc.
365	</p>
366	<p>
367	There are two ways to read image data using this interface. If
368	all the data is to be stored in memory and manipulated at once,
369	then the routine <tt>TIFFReadRGBAImage</tt> can be used:
370	</p>
371	<p>
372	<p style="margin-left: 40px">
373	<tt>#include "tiffio.h"<br>
374	main(int argc, char* argv[])<br>
375	{<br>
376	TIFF* tif = TIFFOpen(argv[1], "r");<br>
377	if (tif) {<br>
378	uint32 w, h;<br>
379	size_t npixels;<br>
380	uint32* raster;<br>
381	<br>
382	TIFFGetField(tif, TIFFTAG_IMAGEWIDTH, &w);<br>
383	TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &h);<br>
384	npixels = w * h;<br>
385	raster = (uint32) _TIFFmalloc(npixels sizeof (uint32));<br>
386	if (raster != NULL) {<br>
387	if (TIFFReadRGBAImage(tif, w, h, raster, 0)) {<br>
388	...process raster data...<br>
389	}<br>
390	_TIFFfree(raster);<br>
391	}<br>
392	TIFFClose(tif);<br>
393	}<br>
394	exit(0);<br>
395	}</tt>
396	</p>
397	<p>
398	Note above that <tt>_TIFFmalloc</tt> is used to allocate memory for
399	the raster passed to <tt>TIFFReadRGBAImage</tt>; this is important
400	to insure the ``appropriate type of memory'' is passed on machines
401	with segmented architectures.
402	</p>
403	<p>
404	Alternatively, <tt>TIFFReadRGBAImage</tt> can be replaced with a
405	more low-level interface that permits an application to have more
406	control over this reading procedure. The equivalent to the above
407	is:
408	</p>
409	<p style="margin-left: 40px">
410	<tt>#include "tiffio.h"<br>
411	main(int argc, char* argv[])<br>
412	{<br>
413	TIFF* tif = TIFFOpen(argv[1], "r");<br>
414	if (tif) {<br>
415	TIFFRGBAImage img;<br>
416	char emsg[1024];<br>
417	<br>
418	if (TIFFRGBAImageBegin(&img, tif, 0, emsg)) {<br>
419	size_t npixels;<br>
420	uint32* raster;<br>
421	<br>
422	npixels = img.width * img.height;<br>
423	raster = (uint32) _TIFFmalloc(npixels sizeof (uint32));<br>
424	if (raster != NULL) {<br>
425	if (TIFFRGBAImageGet(&img, raster, img.width, img.height)) {<br>
426	...process raster data...<br>
427	}<br>
428	_TIFFfree(raster);<br>
429	}<br>
430	TIFFRGBAImageEnd(&img);<br>
431	} else<br>
432	TIFFError(argv[1], emsg);<br>
433	TIFFClose(tif);<br>
434	}<br>
435	exit(0);<br>
436	}</tt>
437	</p>
438	<p>
439	However this usage does not take advantage of the more fine-grained
440	control that's possible. That is, by using this interface it is
441	possible to:
442	</p>
443	<ul>
444	<li>repeatedly fetch (and manipulate) an image without opening
445	and closing the file</li>
446	<li>interpose a method for packing raster pixel data according to
447	application-specific needs (or write the data at all)</li>
448	<li>interpose methods that handle TIFF formats that are not already
449	handled by the core library</li>
450	</ul>
451	<p>
452	The first item means that, for example, image viewers that want to
453	handle multiple files can cache decoding information in order to
454	speedup the work required to display a TIFF image.
455	</p>
456	<p>
457	The second item is the main reason for this interface. By interposing
458	a "put method" (the routine that is called to pack pixel data in
459	the raster) it is possible share the core logic that understands how
460	to deal with TIFF while packing the resultant pixels in a format that
461	is optimized for the application. This alternate format might be very
462	different than the 8-bit per sample ABGR format the library writes by
463	default. For example, if the application is going to display the image
464	on an 8-bit colormap display the put routine might take the data and
465	convert it on-the-fly to the best colormap indices for display.
466	</p>
467	<p>
468	The last item permits an application to extend the library
469	without modifying the core code.
470	By overriding the code provided an application might add support
471	for some esoteric flavor of TIFF that it needs, or it might
472	substitute a packing routine that is able to do optimizations
473	using application/environment-specific information.
474	</p>
475	<p>
476	The TIFF image viewer found in <b>tools/sgigt.c</b> is an example
477	of an application that makes use of the <tt>TIFFRGBAImage</tt>
478	support.
479	</p>
480	<hr>
481	<h2 id="scanlines">Scanline-based Image I/O</h2>
482	<p>
483	The simplest interface provided by <tt>libtiff</tt> is a
484	scanline-oriented interface that can be used to read TIFF
485	images that have their image data organized in strips
486	(trying to use this interface to read data written in tiles
487	will produce errors.)
488	A scanline is a one pixel high row of image data whose width
489	is the width of the image.
490	Data is returned packed if the image data is stored with samples
491	packed together, or as arrays of separate samples if the data
492	is stored with samples separated.
493	The major limitation of the scanline-oriented interface, other
494	than the need to first identify an existing file as having a
495	suitable organization, is that random access to individual
496	scanlines can only be provided when data is not stored in a
497	compressed format, or when the number of rows in a strip
498	of image data is set to one (<tt>RowsPerStrip</tt> is one).
499	</p>
500	<p>
501	Two routines are provided for scanline-based i/o:
502	<tt>TIFFReadScanline</tt>
503	and
504	<tt>TIFFWriteScanline</tt>.
505	For example, to read the contents of a file that
506	is assumed to be organized in strips, the following might be used:
507	</p>
508	<p style="margin-left: 40px">
509	<tt>#include "tiffio.h"<br>
510	main()<br>
511	{<br>
512	TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
513	if (tif) {<br>
514	uint32 imagelength;<br>
515	tdata_t buf;<br>
516	uint32 row;<br>
517	<br>
518	TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imagelength);<br>
519	buf = _TIFFmalloc(TIFFScanlineSize(tif));<br>
520	for (row = 0; row < imagelength; row++)<br>
521	tiffreadscanline(tif, buf, row);<br>
522	_tifffree(buf);<br>
523	tiffclose(tif);<br>
524	}<br>
525	}</tt>
526	</p>
527	<p>
528	<tt>TIFFScanlineSize</tt> returns the number of bytes in
529	a decoded scanline, as returned by <tt>TIFFReadScanline</tt>.
530	Note however that if the file had been create with samples
531	written in separate planes, then the above code would only
532	read data that contained the first sample of each pixel;
533	to handle either case one might use the following instead:
534	</p>
535	<p style="margin-left: 40px">
536	<tt>#include "tiffio.h"<br>
537	main()<br>
538	{<br>
539	TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
540	if (tif) {<br>
541	uint32 imagelength;<br>
542	tdata_t buf;<br>
543	uint32 row;<br>
544	<br>
545	TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imagelength);<br>
546	TIFFGetField(tif, TIFFTAG_PLANARCONFIG, &config);<br>
547	buf = _TIFFmalloc(TIFFScanlineSize(tif));<br>
548	if (config == PLANARCONFIG_CONTIG) {<br>
549	for (row = 0; row < imagelength; row++)<br>
550	tiffreadscanline(tif, buf, row);<br>
551	} else if (config == planarconfig_separate) {<br>
552	uint16 s, nsamples;<br>
553	<br>
554	tiffgetfield(tif, tifftag_samplesperpixel, &nsamples);<br>
555	for (s = 0; s < nsamples; s++)<br>
556	for (row = 0; row < imagelength; row++)<br>
557	tiffreadscanline(tif, buf, row, s);<br>
558	}<br>
559	_tifffree(buf);<br>
560	tiffclose(tif);<br>
561	}<br>
562	}</tt>
563	</p>
564	<p>
565	Beware however that if the following code were used instead to
566	read data in the case <tt>PLANARCONFIG_SEPARATE</tt>,...
567	</p>
568	<p style="margin-left: 40px">
569	<tt>            for (row = 0; row < imagelength; row++)<br>
570	for (s = 0; s < nsamples; s++)<br>
571	tiffreadscanline(tif, buf, row, s);</tt>
572	</p>
573	<p>
574	...then problems would arise if <tt>RowsPerStrip</tt> was not one
575	because the order in which scanlines are requested would require
576	random access to data within strips (something that is not supported
577	by the library when strips are compressed).
578	</p>
579	<hr>
580	<h2 id="strips">Strip-oriented Image I/O</h2>
581	<p>
582	The strip-oriented interfaces provided by the library provide
583	access to entire strips of data. Unlike the scanline-oriented
584	calls, data can be read or written compressed or uncompressed.
585	Accessing data at a strip (or tile) level is often desirable
586	because there are no complications with regard to random access
587	to data within strips.
588	</p>
589	<p>
590	A simple example of reading an image by strips is:
591	</p>
592	<p style="margin-left: 40px">
593	<tt>#include "tiffio.h"<br>
594	main()<br>
595	{<br>
596	TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
597	if (tif) {<br>
598	tdata_t buf;<br>
599	tstrip_t strip;<br>
600	<br>
601	buf = _TIFFmalloc(TIFFStripSize(tif));<br>
602	for (strip = 0; strip < tiffnumberofstrips(tif); strip++)<br>
603	tiffreadencodedstrip(tif, strip, buf, (tsize_t) -1);<br>
604	_tifffree(buf);<br>
605	tiffclose(tif);<br>
606	}<br>
607	}</tt>
608	</p>
609	<p>
610	Notice how a strip size of <tt>-1</tt> is used; <tt>TIFFReadEncodedStrip</tt>
611	will calculate the appropriate size in this case.
612	</p>
613	<p>
614	The above code reads strips in the order in which the
615	data is physically stored in the file. If multiple samples
616	are present and data is stored with <tt>PLANARCONFIG_SEPARATE</tt>
617	then all the strips of data holding the first sample will be
618	read, followed by strips for the second sample, etc.
619	</p>
620	<p>
621	Finally, note that the last strip of data in an image may have fewer
622	rows in it than specified by the <tt>RowsPerStrip</tt> tag. A
623	reader should not assume that each decoded strip contains a full
624	set of rows in it.
625	</p>
626	<p>
627	The following is an example of how to read raw strips of data from
628	a file:
629	</p>
630	<p style="margin-left: 40px">
631	<tt>#include "tiffio.h"<br>
632	main()<br>
633	{<br>
634	TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
635	if (tif) {<br>
636	tdata_t buf;<br>
637	tstrip_t strip;<br>
638	uint32* bc;<br>
639	uint32 stripsize;<br>
640	<br>
641	TIFFGetField(tif, TIFFTAG_STRIPBYTECOUNTS, &bc);<br>
642	stripsize = bc[0];<br>
643	buf = _TIFFmalloc(stripsize);<br>
644	for (strip = 0; strip < tiffnumberofstrips(tif); strip++) {<br>
645	if (bc[strip] > stripsize) {<br>
646	buf = _TIFFrealloc(buf, bc[strip]);<br>
647	stripsize = bc[strip];<br>
648	}<br>
649	TIFFReadRawStrip(tif, strip, buf, bc[strip]);<br>
650	}<br>
651	_TIFFfree(buf);<br>
652	TIFFClose(tif);<br>
653	}<br>
654	}</tt>
655	</p>
656	<p>
657	As above the strips are read in the order in which they are
658	physically stored in the file; this may be different from the
659	logical ordering expected by an application.
660	</p>
661	<hr>
662	<h2 id="tiles">Tile-oriented Image I/O</h2>
663	<p>
664	Tiles of data may be read and written in a manner similar to strips.
665	With this interface, an image is
666	broken up into a set of rectangular areas that may have dimensions
667	less than the image width and height. All the tiles
668	in an image have the same size, and the tile width and length must each
669	be a multiple of 16 pixels. Tiles are ordered left-to-right and
670	top-to-bottom in an image. As for scanlines, samples can be packed
671	contiguously or separately. When separated, all the tiles for a sample
672	are colocated in the file. That is, all the tiles for sample 0 appear
673	before the tiles for sample 1, etc.
674	</p>
675	<p>
676	Tiles and strips may also be extended in a z dimension to form
677	volumes. Data volumes are organized as "slices". That is, all the
678	data for a slice is colocated. Volumes whose data is organized in
679	tiles can also have a tile depth so that data can be organized in
680	cubes.
681	</p>
682	<p>
683	There are actually two interfaces for tiles.
684	One interface is similar to scanlines, to read a tiled image,
685	code of the following sort might be used:
686	</p>
687	<p style="margin-left: 40px">
688	<tt>main()<br>
689	{<br>
690	TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
691	if (tif) {<br>
692	uint32 imageWidth, imageLength;<br>
693	uint32 tileWidth, tileLength;<br>
694	uint32 x, y;<br>
695	tdata_t buf;<br>
696	<br>
697	TIFFGetField(tif, TIFFTAG_IMAGEWIDTH, &imageWidth);<br>
698	TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imageLength);<br>
699	TIFFGetField(tif, TIFFTAG_TILEWIDTH, &tileWidth);<br>
700	TIFFGetField(tif, TIFFTAG_TILELENGTH, &tileLength);<br>
701	buf = _TIFFmalloc(TIFFTileSize(tif));<br>
702	for (y = 0; y < imagelength; y += tilelength)<br>
703	for (x = 0; x < imagewidth; x += tilewidth)<br>
704	tiffreadtile(tif, buf, x, y, 0);<br>
705	_tifffree(buf);<br>
706	tiffclose(tif);<br>
707	}<br>
708	}</tt>
709	</p>
710	<p>
711	(once again, we assume samples are packed contiguously.)
712	</p>
713	<p>
714	Alternatively a direct interface to the low-level data is provided
715	a la strips. Tiles can be read with
716	<tt>TIFFReadEncodedTile</tt> or <tt>TIFFReadRawTile</tt>,
717	and written with <tt>TIFFWriteEncodedTile</tt> or
718	<tt>TIFFWriteRawTile</tt>. For example, to read all the tiles in an image:
719	</p>
720	<p style="margin-left: 40px">
721	<tt>#include "tiffio.h"<br>
722	main()<br>
723	{<br>
724	TIFF* tif = TIFFOpen("myfile.tif", "r");<br>
725	if (tif) {<br>
726	tdata_t buf;<br>
727	ttile_t tile;<br>
728	<br>
729	buf = _TIFFmalloc(TIFFTileSize(tif));<br>
730	for (tile = 0; tile < tiffnumberoftiles(tif); tile++)<br>
731	tiffreadencodedtile(tif, tile, buf, (tsize_t) -1);<br>
732	_tifffree(buf);<br>
733	tiffclose(tif);<br>
734	}<br>
735	}</tt>
736	</p>
737	<hr>
738	<h2 id="other">Other Stuff</h2>
739	<p>
740	Some other stuff will almost certainly go here...
741	</p>
742	<hr>
743	<p>
744	Last updated: $Date: 2005/12/28 06:53:18 $
745	</p>
746	</body>
747	</html>

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