4 * Last changed in libpng 1.6.0 [February 14, 2013]
6 * COPYRIGHT: Written by John Cunningham Bowler, 2013.
7 * To the extent possible under law, the author has waived all copyright and
8 * related or neighboring rights to this work. This work is published from:
11 * Convert 8-bit sRGB or 16-bit linear values to another format.
13 #define _ISOC99_SOURCE 1
25 usage(const char *prog)
28 "%s: usage: %s [-linear|-sRGB] [-gray|-color] component{1,4}\n",
34 component(const char *prog, const char *arg, int issRGB)
37 unsigned long c = strtoul(arg, &ep, 0);
39 if (ep <= arg || *ep || c > 65535 || (issRGB && c > 255))
41 fprintf(stderr, "%s: %s: invalid component value (%lu)\n", prog, arg, c);
49 main(int argc, const char **argv)
51 const char *prog = *argv++;
52 int to_linear = 0, to_gray = 0, to_color = 0;
56 /* FE_TONEAREST is the IEEE754 round to nearest, preferring even, mode; i.e.
57 * everything rounds to the nearest value except that '.5' rounds to the
60 fesetround(FE_TONEAREST);
62 c[3] = c[2] = c[1] = c[0] = 0;
64 while (--argc > 0 && **argv == '-')
66 const char *arg = 1+*argv++;
68 if (strcmp(arg, "sRGB") == 0)
71 else if (strcmp(arg, "linear") == 0)
74 else if (strcmp(arg, "gray") == 0)
75 to_gray = 1, to_color = 0;
77 else if (strcmp(arg, "color") == 0)
78 to_gray = 0, to_color = 1;
91 c[3] = component(prog, argv[3], to_linear);
94 c[2] = component(prog, argv[2], to_linear);
97 c[1] = component(prog, argv[1], to_linear);
100 c[0] = component(prog, argv[0], to_linear);
108 int components = channels;
110 if ((components & 1) == 0)
113 for (i=0; i<components; ++i) c[i] = linear_from_sRGB(c[i] / 255);
114 if (components < channels)
115 c[components] = c[components] / 255;
121 for (i=0; i<4; ++i) c[i] /= 65535;
123 if ((channels & 1) == 0)
125 double alpha = c[channels-1];
128 for (i=0; i<channels-1; ++i) c[i] /= alpha;
130 for (i=0; i<channels-1; ++i) c[i] = 1;
138 fprintf(stderr, "%s: too few channels (%d) for -gray\n",
143 c[0] = YfromRGB(c[0], c[1], c[2]);
151 fprintf(stderr, "%s: too many channels (%d) for -color\n",
156 c[3] = c[1]; /* alpha, if present */
163 if ((channels & 1) == 0)
165 double alpha = c[channels-1];
166 for (i=0; i<channels-1; ++i) c[i] *= alpha;
169 for (i=0; i<channels; ++i) c[i] = nearbyint(c[i] * 65535);
174 int i = (channels+1)&~1;
176 c[i] = sRGB_from_linear(c[i]);
178 for (i=0; i<channels; ++i) c[i] = nearbyint(c[i] * 255);
183 for (i=0; i<channels; ++i) printf(" %g", c[i]);