src/tiff/html/man/TIFFcolor.3tiff.html

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   7 <title>COLOR</title>
   8 </head>
   9 <body>
  10
  11 <h1 align=center>COLOR</h1>
  12 <a href="#NAME">NAME</a><br>
  13 <a href="#SYNOPSIS">SYNOPSIS</a><br>
  14 <a href="#DESCRIPTION">DESCRIPTION</a><br>
  15 <a href="#SEE ALSO">SEE ALSO</a><br>
  16
  17 <hr>
  18 <a name="NAME"></a>
  19 <h2>NAME</h2>
  20 <!-- INDENTATION -->
  21 <table width="100%" border=0 rules="none" frame="void"
  22        cols="2" cellspacing="0" cellpadding="0">
  23 <tr valign="top" align="left">
  24 <td width="8%"></td>
  25 <td width="91%">
  26 <p>TIFFYCbCrToRGBInit, TIFFYCbCrtoRGB, TIFFCIELabToRGBInit,
  27 TIFFCIELabToXYZ, TIFFXYZToRGB &minus; color conversion
  28 routines.</p>
  29 </td>
  30 </table>
  31 <a name="SYNOPSIS"></a>
  32 <h2>SYNOPSIS</h2>
  33 <!-- INDENTATION -->
  34 <table width="100%" border=0 rules="none" frame="void"
  35        cols="2" cellspacing="0" cellpadding="0">
  36 <tr valign="top" align="left">
  37 <td width="8%"></td>
  38 <td width="91%">
  39 <p><b>#include &lt;tiffio.h&gt;</b></p>
  40 <!-- INDENTATION -->
  41 <p><b>int TIFFYCbCrToRGBInit(TIFFYCbCrToRGB
  42 *</b><i>ycbcr</i><b>, float *</b><i>luma</i><b>, float
  43 *</b><i>refBlackWhite&quot;</i><b>);&quot;<br>
  44 void TIFFYCbCrtoRGB(TIFFYCbCrToRGB *</b><i>ycbcr</i><b>,
  45 uint32</b> <i>Y</i><b>, int32</b> <i>Cb</i><b>, int32</b>
  46 <i>Cr</i><b>, uint32 *</b><i>R</i><b>, uint32
  47 *</b><i>G</i><b>, uint32 *</b><i>B</i> <b>);</b></p>
  48 <!-- INDENTATION -->
  49 <p><b>int TIFFCIELabToRGBInit(TIFFCIELabToRGB
  50 *</b><i>cielab</i><b>, TIFFDisplay *</b><i>display</i><b>,
  51 float *</b><i>refWhite</i><b>);<br>
  52 void TIFFCIELabToXYZ(TIFFCIELabToRGB *</b><i>cielab</i><b>,
  53 uint32</b> <i>L</i><b>, int32</b> <i>a</i><b>, int32</b>
  54 <i>b</i><b>, float *</b><i>X</i><b>, float *</b><i>Y</i><b>,
  55 float *</b><i>Z</i><b>);<br>
  56 void TIFFXYZToRGB(TIFFCIELabToRGB *</b><i>cielab</i><b>,
  57 float</b> <i>X</i><b>, float</b> <i>Y</i><b>, float</b>
  58 <i>Z&quot;</i><b>,</b><i>uint32</i><b>*&quot;</b><i>R</i><b>,
  59 uint32 *</b><i>G</i><b>, uint32 *</b><i>B</i><b>);</b></p>
  60 </td>
  61 </table>
  62 <a name="DESCRIPTION"></a>
  63 <h2>DESCRIPTION</h2>
  64 <!-- INDENTATION -->
  65 <table width="100%" border=0 rules="none" frame="void"
  66        cols="2" cellspacing="0" cellpadding="0">
  67 <tr valign="top" align="left">
  68 <td width="8%"></td>
  69 <td width="91%">
  70 <p>TIFF supports several color spaces for images stored in
  71 that format. There is usually a problem of application to
  72 handle the data properly and convert between different
  73 colorspaces for displaying and printing purposes. To
  74 simplify this task libtiff implements several color
  75 conversion routines itself. In particular, these routines
  76 used in <b>TIFFRGBAImage(3TIFF)</b> interface.</p>
  77 <!-- INDENTATION -->
  78 <p><b>TIFFYCbCrToRGBInit()</b> used to initialize
  79 <i>YCbCr</i> to <i>RGB</i> conversion state. Allocating and
  80 freeing of the <i>ycbcr</i> structure belongs to programmer.
  81 <i>TIFFYCbCrToRGB</i> defined in <b>tiffio.h</b> as</p>
  82 </td>
  83 </table>
  84 <!-- INDENTATION -->
  85 <table width="100%" border=0 rules="none" frame="void"
  86        cols="2" cellspacing="0" cellpadding="0">
  87 <tr valign="top" align="left">
  88 <td width="17%"></td>
  89 <td width="82%">
  90 <pre>typedef struct {                /* YCbCr-&gt;RGB support */
  91         TIFFRGBValue* clamptab; /* range clamping table */
  92 </pre>
  93 </td>
  94 </table>
  95 <!-- TABS -->
  96
  97 <table width="100%" border=0 rules="none" frame="void"
  98        cols="5" cellspacing="0" cellpadding="0">
  99 <tr valign="top" align="left">
 100
 101 <p>int*</p>
 102 <td width="28%"></td>
 103 <td width="-3%"></td>
 104 <td width="12%"></td>
 105 <td width="6%">
 106
 107 <p>Cr_r_tab;<br>
 108 int*</p>
 109 </td>
 110 <td width="56%">
 111 </td>
 112 <tr valign="top" align="left">
 113 <td width="28%"></td>
 114 <td width="-3%"></td>
 115 <td width="12%"></td>
 116 <td width="6%">
 117
 118 <p>Cb_b_tab;<br>
 119 int32*</p>
 120 </td>
 121 <td width="56%">
 122 </td>
 123 <tr valign="top" align="left">
 124 <td width="28%"></td>
 125 <td width="-3%"></td>
 126 <td width="12%"></td>
 127 <td width="6%">
 128
 129 <p>Cr_g_tab;<br>
 130 int32*</p>
 131 </td>
 132 <td width="56%">
 133 </td>
 134 <tr valign="top" align="left">
 135 <td width="28%"></td>
 136 <td width="-3%"></td>
 137 <td width="12%"></td>
 138 <td width="6%">
 139
 140 <p>Cb_g_tab;</p>
 141 </td>
 142 <td width="56%">
 143 </td>
 144 </table>
 145 <!-- INDENTATION -->
 146 <table width="100%" border=0 rules="none" frame="void"
 147        cols="2" cellspacing="0" cellpadding="0">
 148 <tr valign="top" align="left">
 149 <td width="17%"></td>
 150 <td width="82%">
 151 <p>int32* Y_tab;<br>
 152 } TIFFYCbCrToRGB;</p></td>
 153 </table>
 154 <!-- INDENTATION -->
 155 <table width="100%" border=0 rules="none" frame="void"
 156        cols="2" cellspacing="0" cellpadding="0">
 157 <tr valign="top" align="left">
 158 <td width="8%"></td>
 159 <td width="91%">
 160 <p><i>luma</i> is a float array of three values representing
 161 proportions of the red, green and blue in luminance, Y (see
 162 section 21 of the TIFF 6.0 specification, where the YCbCr
 163 images discussed). <i>TIFFTAG_YCBCRCOEFFICIENTS</i> holds
 164 that values in TIFF file. <i>refBlackWhite</i> is a float
 165 array of 6 values which specifies a pair of headroom and
 166 footroom image data values (codes) for each image component
 167 (see section 20 of the TIFF 6.0 specification where the
 168 colorinmetry fields discussed).
 169 <i>TIFFTAG_REFERENCEBLACKWHITE</i> is responsible for
 170 storing these values in TIFF file. Following code snippet
 171 should helps to understand the the technique:</p>
 172 </td>
 173 </table>
 174 <!-- INDENTATION -->
 175 <table width="100%" border=0 rules="none" frame="void"
 176        cols="2" cellspacing="0" cellpadding="0">
 177 <tr valign="top" align="left">
 178 <td width="17%"></td>
 179 <td width="82%">
 180 <pre>float *luma, *refBlackWhite;
 181 uint16 hs, vs;
 182
 183 /* Initialize structures */
 184 ycbcr = (TIFFYCbCrToRGB*)
 185 </pre>
 186 </td>
 187 </table>
 188 <!-- TABS -->
 189
 190 <table width="100%" border=0 rules="none" frame="void"
 191        cols="2" cellspacing="0" cellpadding="0">
 192 <tr valign="top" align="left">
 193 <td width="24%"></td>
 194 <td width="75%">
 195
 196 <p>_TIFFmalloc(TIFFroundup(sizeof(TIFFYCbCrToRGB),
 197 sizeof(long))</p>
 198 </td>
 199 <tr valign="top" align="left">
 200 <td width="24%"></td>
 201 <td width="75%">
 202
 203 <p>+ 4*256*sizeof(TIFFRGBValue)</p>
 204 </td>
 205 <tr valign="top" align="left">
 206 <td width="24%"></td>
 207 <td width="75%">
 208
 209 <p>+ 2*256*sizeof(int)</p>
 210 </td>
 211 <tr valign="top" align="left">
 212 <td width="24%"></td>
 213 <td width="75%">
 214
 215 <p>+ 3*256*sizeof(int32));</p>
 216 </td>
 217 </table>
 218 <!-- INDENTATION -->
 219 <table width="100%" border=0 rules="none" frame="void"
 220        cols="2" cellspacing="0" cellpadding="0">
 221 <tr valign="top" align="left">
 222 <td width="17%"></td>
 223 <td width="82%">
 224 <p>if (ycbcr == NULL) {<br>
 225 TIFFError(&quot;YCbCr-&gt;RGB&quot;,</p></td>
 226 </table>
 227 <!-- TABS -->
 228 <table width="100%" border=0 rules="none" frame="void"
 229        cols="4" cellspacing="0" cellpadding="0">
 230 <tr valign="top" align="left">
 231 <td width="24%"></td>
 232 <td width="6%">
 233 </td>
 234 <td width="6%">
 235
 236 <p>&quot;No space for YCbCr-&gt;RGB conversion
 237 state&quot;);</p>
 238 </td>
 239 <td width="62%">
 240 </td>
 241 </table>
 242 <!-- INDENTATION -->
 243 <table width="100%" border=0 rules="none" frame="void"
 244        cols="2" cellspacing="0" cellpadding="0">
 245 <tr valign="top" align="left">
 246 <td width="17%"></td>
 247 <td width="82%">
 248 <p>exit(0);<br>
 249 }</p>
 250 <!-- INDENTATION -->
 251 <p>TIFFGetFieldDefaulted(tif, TIFFTAG_YCBCRCOEFFICIENTS,
 252 &amp;luma);<br>
 253 TIFFGetFieldDefaulted(tif, TIFFTAG_REFERENCEBLACKWHITE,
 254 &amp;refBlackWhite);<br>
 255 if (TIFFYCbCrToRGBInit(ycbcr, luma, refBlackWhite) &lt;
 256 0)</p></td>
 257 </table>
 258 <!-- TABS -->
 259 <table width="100%" border=0 rules="none" frame="void"
 260        cols="2" cellspacing="0" cellpadding="0">
 261 <tr valign="top" align="left">
 262 <td width="24%"></td>
 263 <td width="75%">
 264
 265 <p>exit(0);</p>
 266 </td>
 267 </table>
 268 <!-- INDENTATION -->
 269 <table width="100%" border=0 rules="none" frame="void"
 270        cols="2" cellspacing="0" cellpadding="0">
 271 <tr valign="top" align="left">
 272 <td width="17%"></td>
 273 <td width="82%">
 274 <p>/* Start conversion */<br>
 275 uint32 r, g, b;<br>
 276 uint32 Y;<br>
 277 int32 Cb, Cr;</p>
 278 <!-- INDENTATION -->
 279 <p>for each pixel in image</p></td>
 280 </table>
 281 <!-- TABS -->
 282 <table width="100%" border=0 rules="none" frame="void"
 283        cols="2" cellspacing="0" cellpadding="0">
 284 <tr valign="top" align="left">
 285 <td width="24%"></td>
 286 <td width="75%">
 287
 288 <p>TIFFYCbCrtoRGB(img-&gt;ycbcr, Y, Cb, Cr, &amp;r, &amp;g,
 289 &amp;b);</p>
 290 </td>
 291 </table>
 292 <!-- INDENTATION -->
 293 <table width="100%" border=0 rules="none" frame="void"
 294        cols="2" cellspacing="0" cellpadding="0">
 295 <tr valign="top" align="left">
 296 <td width="17%"></td>
 297 <td width="82%">
 298 <p>/* Free state structure */<br>
 299 _TIFFfree(ycbcr);</p></td>
 300 </table>
 301 <!-- INDENTATION -->
 302 <table width="100%" border=0 rules="none" frame="void"
 303        cols="2" cellspacing="0" cellpadding="0">
 304 <tr valign="top" align="left">
 305 <td width="8%"></td>
 306 <td width="91%">
 307 <p><b>TIFFCIELabToRGBInit()</b> initializes the <i>CIE
 308 L*a*b* 1976</i> to <i>RGB</i> conversion state.
 309 <b>TIFFCIELabToRGB</b> defined as</p>
 310 </td>
 311 </table>
 312 <!-- INDENTATION -->
 313 <table width="100%" border=0 rules="none" frame="void"
 314        cols="2" cellspacing="0" cellpadding="0">
 315 <tr valign="top" align="left">
 316 <td width="17%"></td>
 317 <td width="82%">
 318 <pre>#define CIELABTORGB_TABLE_RANGE 1500
 319
 320 </pre>
 321 </td>
 322 </table>
 323 <!-- TABS -->
 324
 325 <table width="100%" border=0 rules="none" frame="void"
 326        cols="9" cellspacing="0" cellpadding="0">
 327 <tr valign="top" align="left">
 328 <td width="17%"></td>
 329 <td width="6%">
 330
 331 <p>typedef struct {</p>
 332 </td>
 333 <td width="6%"></td>
 334 <td width="6%"></td>
 335 <td width="6%"></td>
 336 <td width="6%">
 337 </td>
 338 <td width="6%">
 339
 340 <p>/* CIE Lab 1976-&gt;RGB support */</p>
 341 </td>
 342 <td width="6%"></td>
 343 <td width="37%">
 344 </td>
 345 <tr valign="top" align="left">
 346 <td width="17%"></td>
 347 <td width="6%">
 348 </td>
 349 <td width="6%">
 350
 351 <p>int</p>
 352 </td>
 353 <td width="6%">
 354
 355 <p>range;</p>
 356 </td>
 357 <td width="6%"></td>
 358 <td width="6%">
 359 </td>
 360 <td width="6%">
 361
 362 <p>/* Size of conversion table */</p>
 363 </td>
 364 <td width="6%"></td>
 365 <td width="37%">
 366 </td>
 367 <tr valign="top" align="left">
 368 <td width="17%"></td>
 369 <td width="6%">
 370 </td>
 371 <td width="6%">
 372
 373 <p>float</p>
 374 </td>
 375 <td width="6%"></td>
 376 <td width="6%">
 377
 378 <p>rstep, gstep, bstep;</p>
 379 </td>
 380 <td width="6%"></td>
 381 <td width="6%"></td>
 382 <td width="6%"></td>
 383 <td width="37%">
 384 </td>
 385 <tr valign="top" align="left">
 386 <td width="17%"></td>
 387 <td width="6%">
 388 </td>
 389 <td width="6%">
 390
 391 <p>float</p>
 392 </td>
 393 <td width="6%"></td>
 394 <td width="6%">
 395
 396 <p>X0, Y0, Z0;</p>
 397 </td>
 398 <td width="6%"></td>
 399 <td width="6%"></td>
 400 <td width="6%">
 401
 402 <p>/* Reference white point */</p>
 403 </td>
 404 <td width="37%">
 405 </td>
 406 <tr valign="top" align="left">
 407 <td width="17%"></td>
 408 <td width="6%"></td>
 409 <td width="6%">
 410
 411 <p>TIFFDisplay display;</p>
 412 </td>
 413 <td width="6%"></td>
 414 <td width="6%"></td>
 415 <td width="6%"></td>
 416 <td width="6%"></td>
 417 <td width="6%"></td>
 418 <td width="37%">
 419 </td>
 420 <tr valign="top" align="left">
 421 <td width="17%"></td>
 422 <td width="6%">
 423 </td>
 424 <td width="6%">
 425
 426 <p>float</p>
 427 </td>
 428 <td width="6%"></td>
 429 <td width="6%">
 430
 431 <p>Yr2r[CIELABTORGB_TABLE_RANGE + 1]; /* Conversion of Yr
 432 to r */</p>
 433 </td>
 434 <td width="6%"></td>
 435 <td width="6%"></td>
 436 <td width="6%"></td>
 437 <td width="37%">
 438 </td>
 439 <tr valign="top" align="left">
 440 <td width="17%"></td>
 441 <td width="6%">
 442 </td>
 443 <td width="6%">
 444
 445 <p>float</p>
 446 </td>
 447 <td width="6%"></td>
 448 <td width="6%">
 449
 450 <p>Yg2g[CIELABTORGB_TABLE_RANGE + 1]; /* Conversion of Yg
 451 to g */</p>
 452 </td>
 453 <td width="6%"></td>
 454 <td width="6%"></td>
 455 <td width="6%"></td>
 456 <td width="37%">
 457 </td>
 458 <tr valign="top" align="left">
 459 <td width="17%"></td>
 460 <td width="6%">
 461 </td>
 462 <td width="6%">
 463
 464 <p>float</p>
 465 </td>
 466 <td width="6%"></td>
 467 <td width="6%">
 468
 469 <p>Yb2b[CIELABTORGB_TABLE_RANGE + 1]; /* Conversion of Yb
 470 to b */</p>
 471 </td>
 472 <td width="6%"></td>
 473 <td width="6%"></td>
 474 <td width="6%"></td>
 475 <td width="37%">
 476 </td>
 477 </table>
 478 <!-- INDENTATION -->
 479 <table width="100%" border=0 rules="none" frame="void"
 480        cols="2" cellspacing="0" cellpadding="0">
 481 <tr valign="top" align="left">
 482 <td width="17%"></td>
 483 <td width="82%">
 484 <p>} TIFFCIELabToRGB;</p></td>
 485 </table>
 486 <!-- INDENTATION -->
 487 <table width="100%" border=0 rules="none" frame="void"
 488        cols="2" cellspacing="0" cellpadding="0">
 489 <tr valign="top" align="left">
 490 <td width="8%"></td>
 491 <td width="91%">
 492 <p><i>display</i> is a display device description, declared
 493 as</p>
 494 </td>
 495 </table>
 496 <!-- INDENTATION -->
 497 <table width="100%" border=0 rules="none" frame="void"
 498        cols="2" cellspacing="0" cellpadding="0">
 499 <tr valign="top" align="left">
 500 <td width="17%"></td>
 501 <td width="82%">
 502 <pre>typedef struct {
 503 </pre>
 504 </td>
 505 </table>
 506 <!-- TABS -->
 507
 508 <table width="100%" border=0 rules="none" frame="void"
 509        cols="2" cellspacing="0" cellpadding="0">
 510 <tr valign="top" align="left">
 511 <td width="24%"></td>
 512 <td width="75%">
 513
 514 <p>float d_mat[3][3]; /* XYZ -&gt; luminance matrix */</p>
 515 </td>
 516 <tr valign="top" align="left">
 517 <td width="24%"></td>
 518 <td width="75%">
 519
 520 <p>float d_YCR; /* Light o/p for reference white */</p>
 521 </td>
 522 <tr valign="top" align="left">
 523 <td width="24%"></td>
 524 <td width="75%">
 525
 526 <p>float d_YCG;</p>
 527 </td>
 528 <tr valign="top" align="left">
 529 <td width="24%"></td>
 530 <td width="75%">
 531
 532 <p>float d_YCB;</p>
 533 </td>
 534 <tr valign="top" align="left">
 535 <td width="24%"></td>
 536 <td width="75%">
 537
 538 <p>uint32 d_Vrwr; /* Pixel values for ref. white */</p>
 539 </td>
 540 <tr valign="top" align="left">
 541 <td width="24%"></td>
 542 <td width="75%">
 543
 544 <p>uint32 d_Vrwg;</p>
 545 </td>
 546 <tr valign="top" align="left">
 547 <td width="24%"></td>
 548 <td width="75%">
 549
 550 <p>uint32 d_Vrwb;</p>
 551 </td>
 552 <tr valign="top" align="left">
 553 <td width="24%"></td>
 554 <td width="75%">
 555
 556 <p>float d_Y0R; /* Residual light for black pixel */</p>
 557 </td>
 558 <tr valign="top" align="left">
 559 <td width="24%"></td>
 560 <td width="75%">
 561
 562 <p>float d_Y0G;</p>
 563 </td>
 564 <tr valign="top" align="left">
 565 <td width="24%"></td>
 566 <td width="75%">
 567
 568 <p>float d_Y0B;</p>
 569 </td>
 570 <tr valign="top" align="left">
 571 <td width="24%"></td>
 572 <td width="75%">
 573
 574 <p>float d_gammaR; /* Gamma values for the three guns
 575 */</p>
 576 </td>
 577 <tr valign="top" align="left">
 578 <td width="24%"></td>
 579 <td width="75%">
 580
 581 <p>float d_gammaG;</p>
 582 </td>
 583 <tr valign="top" align="left">
 584 <td width="24%"></td>
 585 <td width="75%">
 586
 587 <p>float d_gammaB;</p>
 588 </td>
 589 </table>
 590 <!-- INDENTATION -->
 591 <table width="100%" border=0 rules="none" frame="void"
 592        cols="2" cellspacing="0" cellpadding="0">
 593 <tr valign="top" align="left">
 594 <td width="17%"></td>
 595 <td width="82%">
 596 <p>} TIFFDisplay;</p></td>
 597 </table>
 598 <!-- INDENTATION -->
 599 <table width="100%" border=0 rules="none" frame="void"
 600        cols="2" cellspacing="0" cellpadding="0">
 601 <tr valign="top" align="left">
 602 <td width="8%"></td>
 603 <td width="91%">
 604 <p>For example, the one can use sRGB device, which has the
 605 following parameters:</p>
 606 </td>
 607 </table>
 608 <!-- INDENTATION -->
 609 <table width="100%" border=0 rules="none" frame="void"
 610        cols="2" cellspacing="0" cellpadding="0">
 611 <tr valign="top" align="left">
 612 <td width="17%"></td>
 613 <td width="82%">
 614 <pre>TIFFDisplay display_sRGB = {
 615 </pre>
 616 </td>
 617 </table>
 618 <!-- TABS -->
 619
 620 <table width="100%" border=0 rules="none" frame="void"
 621        cols="5" cellspacing="0" cellpadding="0">
 622 <tr valign="top" align="left">
 623 <td width="24%"></td>
 624 <td width="0%"></td>
 625 <td width="6%">
 626
 627 <p>{ /* XYZ -&gt; luminance matrix */</p>
 628 </td>
 629 <td width="6%"></td>
 630 <td width="62%">
 631 </td>
 632 <tr valign="top" align="left">
 633 <td width="24%"></td>
 634 <td width="0%"></td>
 635 <td width="6%">
 636 </td>
 637 <td width="6%">
 638
 639 <p>{ 3.2410F, -1.5374F, -0.4986F },</p>
 640 </td>
 641 <td width="62%">
 642 </td>
 643 <tr valign="top" align="left">
 644 <td width="24%"></td>
 645 <td width="0%"></td>
 646 <td width="6%">
 647 </td>
 648 <td width="6%">
 649
 650 <p>{ -0.9692F, 1.8760F, 0.0416F },</p>
 651 </td>
 652 <td width="62%">
 653 </td>
 654 <tr valign="top" align="left">
 655 <td width="24%"></td>
 656 <td width="0%"></td>
 657 <td width="6%">
 658 </td>
 659 <td width="6%">
 660
 661 <p>{ 0.0556F, -0.2040F, 1.0570F }</p>
 662 </td>
 663 <td width="62%">
 664 </td>
 665 <tr valign="top" align="left">
 666 <td width="24%"></td>
 667 <td width="0%"></td>
 668 <td width="6%">
 669
 670 <p>},</p>
 671 </td>
 672 <td width="6%">
 673 </td>
 674 <td width="62%">
 675 </td>
 676 <tr valign="top" align="left">
 677 <td width="24%"></td>
 678 <td width="0%"></td>
 679 <td width="6%">
 680
 681 <p>100.0F, 100.0F, 100.0F, /* Light o/p for reference white
 682 */</p>
 683 </td>
 684 <td width="6%"></td>
 685 <td width="62%">
 686 </td>
 687 <tr valign="top" align="left">
 688 <td width="24%"></td>
 689 <td width="0%"></td>
 690 <td width="6%">
 691
 692 <p>255, 255, 255, /* Pixel values for ref. white */</p>
 693 </td>
 694 <td width="6%"></td>
 695 <td width="62%">
 696 </td>
 697 <tr valign="top" align="left">
 698 <td width="24%"></td>
 699 <td width="0%"></td>
 700 <td width="6%">
 701
 702 <p>1.0F, 1.0F, 1.0F, /* Residual light o/p for black pixel
 703 */</p>
 704 </td>
 705 <td width="6%"></td>
 706 <td width="62%">
 707 </td>
 708 <tr valign="top" align="left">
 709 <td width="24%"></td>
 710 <td width="0%"></td>
 711 <td width="6%">
 712
 713 <p>2.4F, 2.4F, 2.4F, /* Gamma values for the three guns
 714 */</p>
 715 </td>
 716 <td width="6%"></td>
 717 <td width="62%">
 718 </td>
 719 </table>
 720 <!-- INDENTATION -->
 721 <table width="100%" border=0 rules="none" frame="void"
 722        cols="2" cellspacing="0" cellpadding="0">
 723 <tr valign="top" align="left">
 724 <td width="17%"></td>
 725 <td width="82%">
 726 <p>};</p></td>
 727 </table>
 728 <!-- INDENTATION -->
 729 <table width="100%" border=0 rules="none" frame="void"
 730        cols="2" cellspacing="0" cellpadding="0">
 731 <tr valign="top" align="left">
 732 <td width="8%"></td>
 733 <td width="91%">
 734 <p><i>refWhite</i> is a color temperature of the reference
 735 white. The <i>TIFFTAG_WHITEPOINT</i> contains the
 736 chromaticity of the white point of the image from where the
 737 reference white can be calculated using following
 738 formulae:</p>
 739 </td>
 740 </table>
 741 <!-- INDENTATION -->
 742 <table width="100%" border=0 rules="none" frame="void"
 743        cols="2" cellspacing="0" cellpadding="0">
 744 <tr valign="top" align="left">
 745 <td width="17%"></td>
 746 <td width="82%">
 747 <p>refWhite_Y = 100.0<br>
 748 refWhite_X = whitePoint_x / whitePoint_y * refWhite_Y<br>
 749 refWhite_Z = (1.0 - whitePoint_x - whitePoint_y) /
 750 whitePoint_y * refWhite_X</p></td>
 751 </table>
 752 <!-- INDENTATION -->
 753 <table width="100%" border=0 rules="none" frame="void"
 754        cols="2" cellspacing="0" cellpadding="0">
 755 <tr valign="top" align="left">
 756 <td width="8%"></td>
 757 <td width="91%">
 758 <p>The conversion itself performed in two steps: at the
 759 first one we will convert <i>CIE L*a*b* 1976</i> to <i>CIE
 760 XYZ</i> using <b>TIFFCIELabToXYZ()</b> routine, and at the
 761 second step we will convert <i>CIE XYZ</i> to <i>RGB</i>
 762 using <b>TIFFXYZToRGB().</b> Look at the code sample
 763 below:</p>
 764 </td>
 765 </table>
 766 <!-- INDENTATION -->
 767 <table width="100%" border=0 rules="none" frame="void"
 768        cols="2" cellspacing="0" cellpadding="0">
 769 <tr valign="top" align="left">
 770 <td width="17%"></td>
 771 <td width="82%">
 772 <pre>float   *whitePoint;
 773 float   refWhite[3];
 774
 775 /* Initialize structures */
 776 img-&gt;cielab = (TIFFCIELabToRGB *)
 777 </pre>
 778 </td>
 779 </table>
 780 <!-- TABS -->
 781
 782 <table width="100%" border=0 rules="none" frame="void"
 783        cols="2" cellspacing="0" cellpadding="0">
 784 <tr valign="top" align="left">
 785 <td width="24%"></td>
 786 <td width="75%">
 787
 788 <p>_TIFFmalloc(sizeof(TIFFCIELabToRGB));</p>
 789 </td>
 790 </table>
 791 <!-- INDENTATION -->
 792 <table width="100%" border=0 rules="none" frame="void"
 793        cols="2" cellspacing="0" cellpadding="0">
 794 <tr valign="top" align="left">
 795 <td width="17%"></td>
 796 <td width="82%">
 797 <p>if (!cielab) {</p></td>
 798 </table>
 799 <!-- TABS -->
 800 <table width="100%" border=0 rules="none" frame="void"
 801        cols="5" cellspacing="0" cellpadding="0">
 802 <tr valign="top" align="left">
 803 <td width="24%"></td>
 804 <td width="0%"></td>
 805 <td width="6%">
 806
 807 <p>TIFFError(&quot;CIE L*a*b*-&gt;RGB&quot;,</p>
 808 </td>
 809 <td width="6%"></td>
 810 <td width="62%">
 811 </td>
 812 <tr valign="top" align="left">
 813 <td width="24%"></td>
 814 <td width="0%"></td>
 815 <td width="6%">
 816 </td>
 817 <td width="6%">
 818
 819 <p>&quot;No space for CIE L*a*b*-&gt;RGB conversion
 820 state.&quot;);</p>
 821 </td>
 822 <td width="62%">
 823 </td>
 824 <tr valign="top" align="left">
 825 <td width="24%"></td>
 826 <td width="0%"></td>
 827 <td width="6%">
 828
 829 <p>exit(0);</p>
 830 </td>
 831 <td width="6%"></td>
 832 <td width="62%">
 833 </td>
 834 </table>
 835 <!-- INDENTATION -->
 836 <table width="100%" border=0 rules="none" frame="void"
 837        cols="2" cellspacing="0" cellpadding="0">
 838 <tr valign="top" align="left">
 839 <td width="17%"></td>
 840 <td width="82%">
 841 <p>}</p>
 842 <!-- INDENTATION -->
 843 <p>TIFFGetFieldDefaulted(tif, TIFFTAG_WHITEPOINT,
 844 &amp;whitePoint);<br>
 845 refWhite[1] = 100.0F;<br>
 846 refWhite[0] = whitePoint[0] / whitePoint[1] *
 847 refWhite[1];<br>
 848 refWhite[2] = (1.0F - whitePoint[0] -
 849 whitePoint[1])</p></td>
 850 </table>
 851 <!-- TABS -->
 852 <table width="100%" border=0 rules="none" frame="void"
 853        cols="2" cellspacing="0" cellpadding="0">
 854 <tr valign="top" align="left">
 855 <td width="24%"></td>
 856 <td width="75%">
 857
 858 <p>/ whitePoint[1] * refWhite[1];</p>
 859 </td>
 860 </table>
 861 <!-- INDENTATION -->
 862 <table width="100%" border=0 rules="none" frame="void"
 863        cols="2" cellspacing="0" cellpadding="0">
 864 <tr valign="top" align="left">
 865 <td width="17%"></td>
 866 <td width="82%">
 867 <p>if (TIFFCIELabToRGBInit(cielab, &amp;display_sRGB,
 868 refWhite) &lt; 0) {</p></td>
 869 </table>
 870 <!-- TABS -->
 871 <table width="100%" border=0 rules="none" frame="void"
 872        cols="5" cellspacing="0" cellpadding="0">
 873 <tr valign="top" align="left">
 874 <td width="24%"></td>
 875 <td width="0%"></td>
 876 <td width="6%">
 877
 878 <p>TIFFError(&quot;CIE L*a*b*-&gt;RGB&quot;,</p>
 879 </td>
 880 <td width="6%"></td>
 881 <td width="62%">
 882 </td>
 883 <tr valign="top" align="left">
 884 <td width="24%"></td>
 885 <td width="0%"></td>
 886 <td width="6%">
 887 </td>
 888 <td width="6%">
 889
 890 <p>&quot;Failed to initialize CIE L*a*b*-&gt;RGB conversion
 891 state.&quot;);</p>
 892 </td>
 893 <td width="62%">
 894 </td>
 895 <tr valign="top" align="left">
 896 <td width="24%"></td>
 897 <td width="0%"></td>
 898 <td width="6%">
 899
 900 <p>_TIFFfree(cielab);</p>
 901 </td>
 902 <td width="6%"></td>
 903 <td width="62%">
 904 </td>
 905 <tr valign="top" align="left">
 906 <td width="24%"></td>
 907 <td width="0%"></td>
 908 <td width="6%">
 909
 910 <p>exit(0);</p>
 911 </td>
 912 <td width="6%"></td>
 913 <td width="62%">
 914 </td>
 915 </table>
 916 <!-- INDENTATION -->
 917 <table width="100%" border=0 rules="none" frame="void"
 918        cols="2" cellspacing="0" cellpadding="0">
 919 <tr valign="top" align="left">
 920 <td width="17%"></td>
 921 <td width="82%">
 922 <p>}</p>
 923 <!-- INDENTATION -->
 924 <p>/* Now we can start to convert */<br>
 925 uint32 r, g, b;<br>
 926 uint32 L;<br>
 927 int32 a, b;<br>
 928 float X, Y, Z;</p>
 929 <!-- INDENTATION -->
 930 <p>for each pixel in image</p></td>
 931 </table>
 932 <!-- TABS -->
 933 <table width="100%" border=0 rules="none" frame="void"
 934        cols="2" cellspacing="0" cellpadding="0">
 935 <tr valign="top" align="left">
 936 <td width="24%"></td>
 937 <td width="75%">
 938
 939 <p>TIFFCIELabToXYZ(cielab, L, a, b, &amp;X, &amp;Y,
 940 &amp;Z);</p>
 941 </td>
 942 <tr valign="top" align="left">
 943 <td width="24%"></td>
 944 <td width="75%">
 945
 946 <p>TIFFXYZToRGB(cielab, X, Y, Z, &amp;r, &amp;g,
 947 &amp;b);</p>
 948 </td>
 949 </table>
 950 <!-- INDENTATION -->
 951 <table width="100%" border=0 rules="none" frame="void"
 952        cols="2" cellspacing="0" cellpadding="0">
 953 <tr valign="top" align="left">
 954 <td width="17%"></td>
 955 <td width="82%">
 956 <p>/* Don&rsquo;t forget to free the state structure */<br>
 957 _TIFFfree(cielab);</p></td>
 958 </table>
 959 <a name="SEE ALSO"></a>
 960 <h2>SEE ALSO</h2>
 961 <!-- INDENTATION -->
 962 <table width="100%" border=0 rules="none" frame="void"
 963        cols="2" cellspacing="0" cellpadding="0">
 964 <tr valign="top" align="left">
 965 <td width="8%"></td>
 966 <td width="91%">
 967 <p><b>TIFFRGBAImage</b>(3TIFF) <b>libtiff</b>(3TIFF),</p>
 968 <!-- INDENTATION -->
 969 <p>Libtiff library home page:
 970 <b>http://www.remotesensing.org/libtiff/</b></p>
 971 </td>
 972 </table>
 973 <hr>
 974 </body>
 975 </html>