mupdf中CMYK与RGB的转换算法

来源：互联网发布：excel官方下载mac版本编辑：程序博客网时间：2024/06/17 22:50

之前碰到过RGB与CMYK之间转换的问题，网上也没有比较官方的转换公式，不同的软件可能会采用不同的算法，现在mupdf，正好也看到了这样的算法，还是有一定参考价值的，具体算法如下：

#define MIN(a,b) ( (a) < (b) ? (a) : (b) )
#define MAX(a,b) ( (a) > (b) ? (a) : (b) )
#define CLAMP(x,a,b) ( (x) > (b) ? (b) : ( (x) < (a) ? (a) : (x) ) )

static void cmyk_to_rgb( float *cmyk, float *rgb)
{
#ifdef SLOWCMYK /* from poppler */
float c = cmyk[0], m = cmyk[1], y = cmyk[2], k = cmyk[3];
float c1 = 1 - c, m1 = 1 - m, y1 = 1 - y, k1 = 1 - k;
float r, g, b, x;

/* this is a matrix multiplication, unrolled for performance */
x = c1 * m1 * y1 * k1;/* 0 0 0 0 */
r = g = b = x;
x = c1 * m1 * y1 * k;/* 0 0 0 1 */
r += 0.1373 * x;
g += 0.1216 * x;
b += 0.1255 * x;
x = c1 * m1 * y * k1;/* 0 0 1 0 */
r += x;
g += 0.9490 * x;
x = c1 * m1 * y * k;/* 0 0 1 1 */
r += 0.1098 * x;
g += 0.1020 * x;
x = c1 * m * y1 * k1;/* 0 1 0 0 */
r += 0.9255 * x;
b += 0.5490 * x;
x = c1 * m * y1 * k;/* 0 1 0 1 */
r += 0.1412 * x;
x = c1 * m * y * k1;/* 0 1 1 0 */
r += 0.9294 * x;
g += 0.1098 * x;
b += 0.1412 * x;
x = c1 * m * y * k;/* 0 1 1 1 */
r += 0.1333 * x;
x = c * m1 * y1 * k1;/* 1 0 0 0 */
g += 0.6784 * x;
b += 0.9373 * x;
x = c * m1 * y1 * k;/* 1 0 0 1 */
g += 0.0588 * x;
b += 0.1412 * x;
x = c * m1 * y * k1;/* 1 0 1 0 */
g += 0.6510 * x;
b += 0.3137 * x;
x = c * m1 * y * k;/* 1 0 1 1 */
g += 0.0745 * x;
x = c * m * y1 * k1;/* 1 1 0 0 */
r += 0.1804 * x;
g += 0.1922 * x;
b += 0.5725 * x;
x = c * m * y1 * k;/* 1 1 0 1 */
b += 0.0078 * x;
x = c * m * y * k1;/* 1 1 1 0 */
r += 0.2118 * x;
g += 0.2119 * x;
b += 0.2235 * x;

rgb[0] = CLAMP(r, 0, 1);
rgb[1] = CLAMP(g, 0, 1);
rgb[2] = CLAMP(b, 0, 1);
#else
rgb[0] = 1 - MIN(1, cmyk[0] + cmyk[3]);
rgb[1] = 1 - MIN(1, cmyk[1] + cmyk[3]);
rgb[2] = 1 - MIN(1, cmyk[2] + cmyk[3]);
#endif
}

static void rgb_to_cmyk(float *rgb, float *cmyk)
{
float c, m, y, k;
c = 1 - rgb[0];
m = 1 - rgb[1];
y = 1 - rgb[2];
k = MIN(c, MIN(m, y));
cmyk[0] = c - k;
cmyk[1] = m - k;
cmyk[2] = y - k;
cmyk[3] = k;
}

#define MIN(a,b) ( (a) < (b) ? (a) : (b) )
#define MAX(a,b) ( (a) > (b) ? (a) : (b) )
#define CLAMP(x,a,b) ( (x) > (b) ? (b) : ( (x) < (a) ? (a) : (x) ) )

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