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 --> 11 </style> 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.simplesystems.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: 2016-09-25 20:05:44 $ 745 </p> 746</body> 747</html> 748
