4 * Copyright (C) 2017-2018, 2022, D. R. Commander.
5 * For conditions of distribution and use, see the accompanying README.ijg
8 * This file contains convenience functions for performing quick & dirty
9 * CMYK<->RGB conversion. This algorithm is suitable for testing purposes
10 * only. Properly converting between CMYK and RGB requires a color management
18 #define JPEG_INTERNALS
20 #include "jsamplecomp.h"
23 /* Fully reversible */
27 rgb_to_cmyk(_JSAMPLE r, _JSAMPLE g, _JSAMPLE b,
28 _JSAMPLE *c, _JSAMPLE *m, _JSAMPLE *y, _JSAMPLE *k)
30 double ctmp = 1.0 - ((double)r / (double)_MAXJSAMPLE);
31 double mtmp = 1.0 - ((double)g / (double)_MAXJSAMPLE);
32 double ytmp = 1.0 - ((double)b / (double)_MAXJSAMPLE);
33 double ktmp = MIN(MIN(ctmp, mtmp), ytmp);
35 if (ktmp == 1.0) ctmp = mtmp = ytmp = 0.0;
37 ctmp = (ctmp - ktmp) / (1.0 - ktmp);
38 mtmp = (mtmp - ktmp) / (1.0 - ktmp);
39 ytmp = (ytmp - ktmp) / (1.0 - ktmp);
41 *c = (_JSAMPLE)((double)_MAXJSAMPLE - ctmp * (double)_MAXJSAMPLE + 0.5);
42 *m = (_JSAMPLE)((double)_MAXJSAMPLE - mtmp * (double)_MAXJSAMPLE + 0.5);
43 *y = (_JSAMPLE)((double)_MAXJSAMPLE - ytmp * (double)_MAXJSAMPLE + 0.5);
44 *k = (_JSAMPLE)((double)_MAXJSAMPLE - ktmp * (double)_MAXJSAMPLE + 0.5);
48 /* Fully reversible only for C/M/Y/K values generated with rgb_to_cmyk() */
52 cmyk_to_rgb(_JSAMPLE c, _JSAMPLE m, _JSAMPLE y, _JSAMPLE k,
53 _JSAMPLE *r, _JSAMPLE *g, _JSAMPLE *b)
55 *r = (_JSAMPLE)((double)c * (double)k / (double)_MAXJSAMPLE + 0.5);
56 *g = (_JSAMPLE)((double)m * (double)k / (double)_MAXJSAMPLE + 0.5);
57 *b = (_JSAMPLE)((double)y * (double)k / (double)_MAXJSAMPLE + 0.5);