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Comparing ray/src/common/spec_rgb.c (file contents):
Revision 1.2 by greg, Sat Dec 8 09:29:10 1990 UTC vs.
Revision 2.11 by greg, Sat Feb 22 02:07:22 2003 UTC

# Line 1 | Line 1
1 – /* Copyright (c) 1990 Regents of the University of California */
2 –
1   #ifndef lint
2 < static char SCCSid[] = "$SunId$ LBL";
2 > static const char       RCSid[] = "$Id$";
3   #endif
6 –
4   /*
5   * Convert colors and spectral ranges.
6 + * Added von Kries white-balance calculations 10/01 (GW).
7 + *
8 + * Externals declared in color.h
9   */
10  
11 + /* ====================================================================
12 + * The Radiance Software License, Version 1.0
13 + *
14 + * Copyright (c) 1990 - 2002 The Regents of the University of California,
15 + * through Lawrence Berkeley National Laboratory.   All rights reserved.
16 + *
17 + * Redistribution and use in source and binary forms, with or without
18 + * modification, are permitted provided that the following conditions
19 + * are met:
20 + *
21 + * 1. Redistributions of source code must retain the above copyright
22 + *         notice, this list of conditions and the following disclaimer.
23 + *
24 + * 2. Redistributions in binary form must reproduce the above copyright
25 + *       notice, this list of conditions and the following disclaimer in
26 + *       the documentation and/or other materials provided with the
27 + *       distribution.
28 + *
29 + * 3. The end-user documentation included with the redistribution,
30 + *           if any, must include the following acknowledgment:
31 + *             "This product includes Radiance software
32 + *                 (http://radsite.lbl.gov/)
33 + *                 developed by the Lawrence Berkeley National Laboratory
34 + *               (http://www.lbl.gov/)."
35 + *       Alternately, this acknowledgment may appear in the software itself,
36 + *       if and wherever such third-party acknowledgments normally appear.
37 + *
38 + * 4. The names "Radiance," "Lawrence Berkeley National Laboratory"
39 + *       and "The Regents of the University of California" must
40 + *       not be used to endorse or promote products derived from this
41 + *       software without prior written permission. For written
42 + *       permission, please contact [email protected].
43 + *
44 + * 5. Products derived from this software may not be called "Radiance",
45 + *       nor may "Radiance" appear in their name, without prior written
46 + *       permission of Lawrence Berkeley National Laboratory.
47 + *
48 + * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
49 + * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
50 + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
51 + * DISCLAIMED.   IN NO EVENT SHALL Lawrence Berkeley National Laboratory OR
52 + * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
53 + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
54 + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
55 + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
56 + * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
57 + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
58 + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
59 + * SUCH DAMAGE.
60 + * ====================================================================
61 + *
62 + * This software consists of voluntary contributions made by many
63 + * individuals on behalf of Lawrence Berkeley National Laboratory.   For more
64 + * information on Lawrence Berkeley National Laboratory, please see
65 + * <http://www.lbl.gov/>.
66 + */
67 +
68   #include "color.h"
69 + #include <string.h>
70  
71 + #define CEPS    1e-4                    /* color epsilon */
72 +
73 + #define CEQ(v1,v2)      ((v1) <= (v2)+CEPS && (v2) <= (v1)+CEPS)
74 +
75 + #define XYEQ(c1,c2)     (CEQ((c1)[CIEX],(c2)[CIEX]) && CEQ((c1)[CIEY],(c2)[CIEY]))
76 +
77 +
78 + RGBPRIMS  stdprims = STDPRIMS;  /* standard primary chromaticities */
79 +
80 + COLOR  cblack = BLKCOLOR;               /* global black color */
81 + COLOR  cwhite = WHTCOLOR;               /* global white color */
82 +
83 + float  xyneu[2] = {1./3., 1./3.};       /* neutral xy chromaticities */
84 +
85   /*
86   *      The following table contains the CIE tristimulus integrals
87   *  for X, Y, and Z.  The table is cumulative, so that
# Line 39 | Line 111 | static BYTE  chroma[3][NINC] = {
111          }
112   };
113  
114 < #ifdef  NTSC
115 < static float  xyz2rgbmat[3][3] = {      /* XYZ to RGB (NTSC */
116 <        1.73, -.48, -.26,
117 <        -.81, 1.65, -.02,
118 <         .08, -.17, 1.28,
114 > COLORMAT  xyz2rgbmat = {                /* XYZ to RGB (no white balance) */
115 >        {(CIE_y_g - CIE_y_b - CIE_x_b*CIE_y_g + CIE_y_b*CIE_x_g)/CIE_C_rD,
116 >         (CIE_x_b - CIE_x_g - CIE_x_b*CIE_y_g + CIE_x_g*CIE_y_b)/CIE_C_rD,
117 >         (CIE_x_g*CIE_y_b - CIE_x_b*CIE_y_g)/CIE_C_rD},
118 >        {(CIE_y_b - CIE_y_r - CIE_y_b*CIE_x_r + CIE_y_r*CIE_x_b)/CIE_C_gD,
119 >         (CIE_x_r - CIE_x_b - CIE_x_r*CIE_y_b + CIE_x_b*CIE_y_r)/CIE_C_gD,
120 >         (CIE_x_b*CIE_y_r - CIE_x_r*CIE_y_b)/CIE_C_gD},
121 >        {(CIE_y_r - CIE_y_g - CIE_y_r*CIE_x_g + CIE_y_g*CIE_x_r)/CIE_C_bD,
122 >         (CIE_x_g - CIE_x_r - CIE_x_g*CIE_y_r + CIE_x_r*CIE_y_g)/CIE_C_bD,
123 >         (CIE_x_r*CIE_y_g - CIE_x_g*CIE_y_r)/CIE_C_bD}
124   };
125 < #else
126 < static float xyz2rgbmat[3][3] = {       /* XYZ to RGB (color monitor) */
127 <         2.739, -1.145, -.424,
128 <        -1.119,  2.029,  .033,
129 <          .138,  -.333, 1.105,
125 >
126 > COLORMAT  rgb2xyzmat = {                /* RGB to XYZ (no white balance) */
127 >        {CIE_x_r*CIE_C_rD/CIE_D,CIE_x_g*CIE_C_gD/CIE_D,CIE_x_b*CIE_C_bD/CIE_D},
128 >        {CIE_y_r*CIE_C_rD/CIE_D,CIE_y_g*CIE_C_gD/CIE_D,CIE_y_b*CIE_C_bD/CIE_D},
129 >        {(1.-CIE_x_r-CIE_y_r)*CIE_C_rD/CIE_D,
130 >         (1.-CIE_x_g-CIE_y_g)*CIE_C_gD/CIE_D,
131 >         (1.-CIE_x_b-CIE_y_b)*CIE_C_bD/CIE_D}
132   };
54 – #endif
133  
134 + COLORMAT  vkmat = {             /* Sharp primary matrix */
135 +        { 1.2694, -0.0988, -0.1706},
136 +        {-0.8364,  1.8006,  0.0357},
137 +        { 0.0297, -0.0315,  1.0018}
138 + };
139  
140 + COLORMAT  ivkmat = {            /* inverse Sharp primary matrix */
141 +        { 0.8156,  0.0472,  0.1372},
142 +        { 0.3791,  0.5769,  0.0440},
143 +        {-0.0123,  0.0167,  0.9955}
144 + };
145  
146 +
147 + void
148   spec_rgb(col, s, e)             /* compute RGB color from spectral range */
149   COLOR  col;
150   int  s, e;
# Line 66 | Line 156 | int  s, e;
156   }
157  
158  
159 + void
160   spec_cie(col, s, e)             /* compute a color from a spectral range */
161   COLOR  col;             /* returned color */
162   int  s, e;              /* starting and ending wavelengths */
# Line 78 | Line 169 | int  s, e;             /* starting and ending wavelengths */
169  
170          e -= STARTWL;
171          if (e <= s) {
172 <                col[RED] = col[GRN] = col[BLU] = 0.0;
172 >                col[CIEX] = col[CIEY] = col[CIEZ] = 0.0;
173                  return;
174          }
175          if (e >= INCWL*(NINC - 1))
# Line 94 | Line 185 | int  s, e;             /* starting and ending wavelengths */
185          for (i = 0; i < 3; i++)
186                  col[i] -= chroma[i][d]*(INCWL - r) - chroma[i][d + 1]*r;
187  
188 <        col[RED] = (col[RED] + 0.5) / (256*INCWL);
189 <        col[GRN] = (col[GRN] + 0.5) / (256*INCWL);
190 <        col[BLU] = (col[BLU] + 0.5) / (256*INCWL);
188 >        col[CIEX] = (col[CIEX] + 0.5) * (1./(256*INCWL));
189 >        col[CIEY] = (col[CIEY] + 0.5) * (1./(256*INCWL));
190 >        col[CIEZ] = (col[CIEZ] + 0.5) * (1./(256*INCWL));
191   }
192  
193  
194 < cie_rgb(rgbcolor, ciecolor)             /* convert CIE to RGB (NTSC) */
195 < register COLOR  rgbcolor, ciecolor;
194 > void
195 > cie_rgb(rgb, xyz)               /* convert CIE color to standard RGB */
196 > COLOR   rgb;
197 > COLOR  xyz;
198   {
199 +        colortrans(rgb, xyz2rgbmat, xyz);
200 +        clipgamut(rgb, xyz[CIEY], CGAMUT_LOWER, cblack, cwhite);
201 + }
202 +
203 +
204 + int
205 + clipgamut(col, brt, gamut, lower, upper)        /* clip to gamut cube */
206 + COLOR  col;
207 + double  brt;
208 + int  gamut;
209 + COLOR  lower, upper;
210 + {
211 +        int  rflags = 0;
212 +        double  brtmin, brtmax, v, vv;
213 +        COLOR  cgry;
214          register int  i;
215 +                                        /* check for no check */
216 +        if (gamut == 0) return(0);
217 +                                        /* check brightness limits */
218 +        brtmin = 1./3.*(lower[0]+lower[1]+lower[2]);
219 +        if (gamut & CGAMUT_LOWER && brt < brtmin) {
220 +                copycolor(col, lower);
221 +                return(CGAMUT_LOWER);
222 +        }
223 +        brtmax = 1./3.*(upper[0]+upper[1]+upper[2]);
224 +        if (gamut & CGAMUT_UPPER && brt > brtmax) {
225 +                copycolor(col, upper);
226 +                return(CGAMUT_UPPER);
227 +        }
228 +                                        /* compute equivalent grey */
229 +        v = (brt - brtmin)/(brtmax - brtmin);
230 +        for (i = 0; i < 3; i++)
231 +                cgry[i] = v*upper[i] + (1.-v)*lower[i];
232 +        vv = 1.;                        /* check each limit */
233 +        for (i = 0; i < 3; i++)
234 +                if (gamut & CGAMUT_LOWER && col[i] < lower[i]) {
235 +                        v = (lower[i]+CEPS - cgry[i])/(col[i] - cgry[i]);
236 +                        if (v < vv) vv = v;
237 +                        rflags |= CGAMUT_LOWER;
238 +                } else if (gamut & CGAMUT_UPPER && col[i] > upper[i]) {
239 +                        v = (upper[i]-CEPS - cgry[i])/(col[i] - cgry[i]);
240 +                        if (v < vv) vv = v;
241 +                        rflags |= CGAMUT_UPPER;
242 +                }
243 +        if (rflags)                     /* desaturate to cube face */
244 +                for (i = 0; i < 3; i++)
245 +                        col[i] = vv*col[i] + (1.-vv)*cgry[i];
246 +        return(rflags);
247 + }
248  
249 <        for (i = 0; i < 3; i++) {
250 <                rgbcolor[i] =   xyz2rgbmat[i][0]*ciecolor[0] +
251 <                                xyz2rgbmat[i][1]*ciecolor[1] +
252 <                                xyz2rgbmat[i][2]*ciecolor[2] ;
253 <                if (rgbcolor[i] < 0.0)
254 <                        rgbcolor[i] = 0.0;
249 >
250 > void
251 > colortrans(c2, mat, c1)         /* convert c1 by mat and put into c2 */
252 > register COLOR  c2;
253 > register COLORMAT  mat;
254 > register COLOR  c1;
255 > {
256 >        COLOR   cout;
257 >
258 >        cout[0] = mat[0][0]*c1[0] + mat[0][1]*c1[1] + mat[0][2]*c1[2];
259 >        cout[1] = mat[1][0]*c1[0] + mat[1][1]*c1[1] + mat[1][2]*c1[2];
260 >        cout[2] = mat[2][0]*c1[0] + mat[2][1]*c1[1] + mat[2][2]*c1[2];
261 >
262 >        copycolor(c2, cout);
263 > }
264 >
265 >
266 > void
267 > multcolormat(m3, m2, m1)        /* multiply m1 by m2 and put into m3 */
268 > COLORMAT  m3;                   /* m3 can be either m1 or m2 w/o harm */
269 > COLORMAT  m2, m1;
270 > {
271 >        COLORMAT  mt;
272 >        register int  i, j;
273 >
274 >        for (i = 0; i < 3; i++)
275 >                for (j = 0; j < 3; j++)
276 >                        mt[i][j] =      m1[i][0]*m2[0][j] +
277 >                                        m1[i][1]*m2[1][j] +
278 >                                        m1[i][2]*m2[2][j] ;
279 >        cpcolormat(m3, mt);
280 > }
281 >
282 >
283 > void
284 > compxyz2rgbmat(mat, pr)         /* compute conversion from CIE to RGB space */
285 > COLORMAT  mat;
286 > register RGBPRIMS  pr;
287 > {
288 >        double  C_rD, C_gD, C_bD;
289 >
290 >        if (pr == stdprims) {   /* can use xyz2rgbmat */
291 >                cpcolormat(mat, xyz2rgbmat);
292 >                return;
293          }
294 +        C_rD = (1./pr[WHT][CIEY]) *
295 +                        ( pr[WHT][CIEX]*(pr[GRN][CIEY] - pr[BLU][CIEY]) -
296 +                          pr[WHT][CIEY]*(pr[GRN][CIEX] - pr[BLU][CIEX]) +
297 +                  pr[GRN][CIEX]*pr[BLU][CIEY] - pr[BLU][CIEX]*pr[GRN][CIEY] ) ;
298 +        C_gD = (1./pr[WHT][CIEY]) *
299 +                        ( pr[WHT][CIEX]*(pr[BLU][CIEY] - pr[RED][CIEY]) -
300 +                          pr[WHT][CIEY]*(pr[BLU][CIEX] - pr[RED][CIEX]) -
301 +                  pr[RED][CIEX]*pr[BLU][CIEY] + pr[BLU][CIEX]*pr[RED][CIEY] ) ;
302 +        C_bD = (1./pr[WHT][CIEY]) *
303 +                        ( pr[WHT][CIEX]*(pr[RED][CIEY] - pr[GRN][CIEY]) -
304 +                          pr[WHT][CIEY]*(pr[RED][CIEX] - pr[GRN][CIEX]) +
305 +                  pr[RED][CIEX]*pr[GRN][CIEY] - pr[GRN][CIEX]*pr[RED][CIEY] ) ;
306 +
307 +        mat[0][0] = (pr[GRN][CIEY] - pr[BLU][CIEY] -
308 +                        pr[BLU][CIEX]*pr[GRN][CIEY] +
309 +                        pr[BLU][CIEY]*pr[GRN][CIEX])/C_rD ;
310 +        mat[0][1] = (pr[BLU][CIEX] - pr[GRN][CIEX] -
311 +                        pr[BLU][CIEX]*pr[GRN][CIEY] +
312 +                        pr[GRN][CIEX]*pr[BLU][CIEY])/C_rD ;
313 +        mat[0][2] = (pr[GRN][CIEX]*pr[BLU][CIEY] -
314 +                        pr[BLU][CIEX]*pr[GRN][CIEY])/C_rD ;
315 +        mat[1][0] = (pr[BLU][CIEY] - pr[RED][CIEY] -
316 +                        pr[BLU][CIEY]*pr[RED][CIEX] +
317 +                        pr[RED][CIEY]*pr[BLU][CIEX])/C_gD ;
318 +        mat[1][1] = (pr[RED][CIEX] - pr[BLU][CIEX] -
319 +                        pr[RED][CIEX]*pr[BLU][CIEY] +
320 +                        pr[BLU][CIEX]*pr[RED][CIEY])/C_gD ;
321 +        mat[1][2] = (pr[BLU][CIEX]*pr[RED][CIEY] -
322 +                        pr[RED][CIEX]*pr[BLU][CIEY])/C_gD ;
323 +        mat[2][0] = (pr[RED][CIEY] - pr[GRN][CIEY] -
324 +                        pr[RED][CIEY]*pr[GRN][CIEX] +
325 +                        pr[GRN][CIEY]*pr[RED][CIEX])/C_bD ;
326 +        mat[2][1] = (pr[GRN][CIEX] - pr[RED][CIEX] -
327 +                        pr[GRN][CIEX]*pr[RED][CIEY] +
328 +                        pr[RED][CIEX]*pr[GRN][CIEY])/C_bD ;
329 +        mat[2][2] = (pr[RED][CIEX]*pr[GRN][CIEY] -
330 +                        pr[GRN][CIEX]*pr[RED][CIEY])/C_bD ;
331 + }
332 +
333 +
334 + void
335 + comprgb2xyzmat(mat, pr)         /* compute conversion from RGB to CIE space */
336 + COLORMAT  mat;
337 + register RGBPRIMS  pr;
338 + {
339 +        double  C_rD, C_gD, C_bD, D;
340 +
341 +        if (pr == stdprims) {   /* can use rgb2xyzmat */
342 +                cpcolormat(mat, rgb2xyzmat);
343 +                return;
344 +        }
345 +        C_rD = (1./pr[WHT][CIEY]) *
346 +                        ( pr[WHT][CIEX]*(pr[GRN][CIEY] - pr[BLU][CIEY]) -
347 +                          pr[WHT][CIEY]*(pr[GRN][CIEX] - pr[BLU][CIEX]) +
348 +                  pr[GRN][CIEX]*pr[BLU][CIEY] - pr[BLU][CIEX]*pr[GRN][CIEY] ) ;
349 +        C_gD = (1./pr[WHT][CIEY]) *
350 +                        ( pr[WHT][CIEX]*(pr[BLU][CIEY] - pr[RED][CIEY]) -
351 +                          pr[WHT][CIEY]*(pr[BLU][CIEX] - pr[RED][CIEX]) -
352 +                  pr[RED][CIEX]*pr[BLU][CIEY] + pr[BLU][CIEX]*pr[RED][CIEY] ) ;
353 +        C_bD = (1./pr[WHT][CIEY]) *
354 +                        ( pr[WHT][CIEX]*(pr[RED][CIEY] - pr[GRN][CIEY]) -
355 +                          pr[WHT][CIEY]*(pr[RED][CIEX] - pr[GRN][CIEX]) +
356 +                  pr[RED][CIEX]*pr[GRN][CIEY] - pr[GRN][CIEX]*pr[RED][CIEY] ) ;
357 +        D = pr[RED][CIEX]*(pr[GRN][CIEY] - pr[BLU][CIEY]) +
358 +                        pr[GRN][CIEX]*(pr[BLU][CIEY] - pr[RED][CIEY]) +
359 +                        pr[BLU][CIEX]*(pr[RED][CIEY] - pr[GRN][CIEY]) ;
360 +        mat[0][0] = pr[RED][CIEX]*C_rD/D;
361 +        mat[0][1] = pr[GRN][CIEX]*C_gD/D;
362 +        mat[0][2] = pr[BLU][CIEX]*C_bD/D;
363 +        mat[1][0] = pr[RED][CIEY]*C_rD/D;
364 +        mat[1][1] = pr[GRN][CIEY]*C_gD/D;
365 +        mat[1][2] = pr[BLU][CIEY]*C_bD/D;
366 +        mat[2][0] = (1.-pr[RED][CIEX]-pr[RED][CIEY])*C_rD/D;
367 +        mat[2][1] = (1.-pr[GRN][CIEX]-pr[GRN][CIEY])*C_gD/D;
368 +        mat[2][2] = (1.-pr[BLU][CIEX]-pr[BLU][CIEY])*C_bD/D;
369 + }
370 +
371 +
372 + void
373 + comprgb2rgbmat(mat, pr1, pr2)   /* compute conversion from RGB1 to RGB2 */
374 + COLORMAT  mat;
375 + RGBPRIMS  pr1, pr2;
376 + {
377 +        COLORMAT  pr1toxyz, xyztopr2;
378 +
379 +        if (pr1 == pr2) {
380 +                mat[0][0] = mat[1][1] = mat[2][2] = 1.0;
381 +                mat[0][1] = mat[0][2] = mat[1][0] =
382 +                mat[1][2] = mat[2][0] = mat[2][1] = 0.0;
383 +                return;
384 +        }
385 +        comprgb2xyzmat(pr1toxyz, pr1);
386 +        compxyz2rgbmat(xyztopr2, pr2);
387 +                                /* combine transforms */
388 +        multcolormat(mat, pr1toxyz, xyztopr2);
389 + }
390 +
391 +
392 + void
393 + compxyzWBmat(mat, wht1, wht2)   /* CIE von Kries transform from wht1 to wht2 */
394 + COLORMAT  mat;
395 + float  wht1[2], wht2[2];
396 + {
397 +        COLOR   cw1, cw2;
398 +        if (XYEQ(wht1,wht2)) {
399 +                mat[0][0] = mat[1][1] = mat[2][2] = 1.0;
400 +                mat[0][1] = mat[0][2] = mat[1][0] =
401 +                mat[1][2] = mat[2][0] = mat[2][1] = 0.0;
402 +                return;
403 +        }
404 +        cw1[RED] = wht1[CIEX]/wht1[CIEY];
405 +        cw1[GRN] = 1.;
406 +        cw1[BLU] = (1. - wht1[CIEX] - wht1[CIEY])/wht1[CIEY];
407 +        colortrans(cw1, vkmat, cw1);
408 +        cw2[RED] = wht2[CIEX]/wht2[CIEY];
409 +        cw2[GRN] = 1.;
410 +        cw2[BLU] = (1. - wht2[CIEX] - wht2[CIEY])/wht2[CIEY];
411 +        colortrans(cw2, vkmat, cw2);
412 +        mat[0][0] = cw2[RED]/cw1[RED];
413 +        mat[1][1] = cw2[GRN]/cw1[GRN];
414 +        mat[2][2] = cw2[BLU]/cw1[BLU];
415 +        mat[0][1] = mat[0][2] = mat[1][0] =
416 +        mat[1][2] = mat[2][0] = mat[2][1] = 0.0;
417 +        multcolormat(mat, vkmat, mat);
418 +        multcolormat(mat, mat, ivkmat);
419 + }
420 +
421 +
422 + void
423 + compxyz2rgbWBmat(mat, pr)       /* von Kries conversion from CIE to RGB space */
424 + COLORMAT  mat;
425 + RGBPRIMS  pr;
426 + {
427 +        COLORMAT        wbmat;
428 +
429 +        compxyz2rgbmat(mat, pr);
430 +        if (XYEQ(pr[WHT],xyneu))
431 +                return;
432 +        compxyzWBmat(wbmat, xyneu, pr[WHT]);
433 +        multcolormat(mat, wbmat, mat);
434 + }
435 +
436 + void
437 + comprgb2xyzWBmat(mat, pr)       /* von Kries conversion from RGB to CIE space */
438 + COLORMAT  mat;
439 + RGBPRIMS  pr;
440 + {
441 +        COLORMAT        wbmat;
442 +        
443 +        comprgb2xyzmat(mat, pr);
444 +        if (XYEQ(pr[WHT],xyneu))
445 +                return;
446 +        compxyzWBmat(wbmat, pr[WHT], xyneu);
447 +        multcolormat(mat, mat, wbmat);
448 + }
449 +
450 + void
451 + comprgb2rgbWBmat(mat, pr1, pr2) /* von Kries conversion from RGB1 to RGB2 */
452 + COLORMAT  mat;
453 + RGBPRIMS  pr1, pr2;
454 + {
455 +        COLORMAT  pr1toxyz, xyztopr2, wbmat;
456 +
457 +        if (pr1 == pr2) {
458 +                mat[0][0] = mat[1][1] = mat[2][2] = 1.0;
459 +                mat[0][1] = mat[0][2] = mat[1][0] =
460 +                mat[1][2] = mat[2][0] = mat[2][1] = 0.0;
461 +                return;
462 +        }
463 +        comprgb2xyzmat(pr1toxyz, pr1);
464 +        compxyzWBmat(wbmat, pr1[WHT], pr2[WHT]);
465 +        compxyz2rgbmat(xyztopr2, pr2);
466 +                                /* combine transforms */
467 +        multcolormat(mat, pr1toxyz, wbmat);
468 +        multcolormat(mat, mat, xyztopr2);
469   }

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