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@mity mity/hsv.c
Created Jul 18, 2013

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RGB <--> HSV color conversion functions for Windows, in integer arithmetics.
/*
* RGB <--> HSV conversion in integer arithmetics, to be used on Windows.
* Copyright (c) 2013 Martin Mitas
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#include "hsv.h"
#define MIN(a,b) ((a) < (b) ? (a) : (b))
#define MAX(a,b) ((a) > (b) ? (a) : (b))
#define MIN3(a,b,c) MIN((a), MIN((b), (c)))
#define MAX3(a,b,c) MAX((a), MAX((b), (c)))
void
rgb2hsv(COLORREF rgb, hsv_t* hsv)
{
int r = GetRValue(rgb);
int g = GetGValue(rgb);
int b = GetBValue(rgb);
int m = MIN3(r, g, b);
int M = MAX3(r, g, b);
int delta = M - m;
if(delta == 0) {
/* Achromatic case (i.e. grayscale) */
hsv->hue = -1; /* undefined */
hsv->saturation = 0;
} else {
int h;
if(r == M)
h = ((g-b)*60*HUE_DEGREE) / delta;
else if(g == M)
h = ((b-r)*60*HUE_DEGREE) / delta + 120*HUE_DEGREE;
else /*if(b == M)*/
h = ((r-g)*60*HUE_DEGREE) / delta + 240*HUE_DEGREE;
if(h < 0)
h += 360*HUE_DEGREE;
hsv->hue = h;
/* The constatnt 8 is tuned to statistically cause as little
* tolerated mismatches as possible in RGB -> HSV -> RGB conversion.
* (See the unit test at the bottom of this file.)
*/
hsv->saturation = (256*delta-8) / M;
}
hsv->value = M;
}
COLORREF
hsv2rgb(hsv_t* hsv)
{
BYTE r, g, b;
if(hsv->saturation == 0) {
r = g = b = hsv->value;
} else {
int h = hsv->hue;
int s = hsv->saturation;
int v = hsv->value;
int i = h / (60*HUE_DEGREE);
int p = (256*v - s*v) / 256;
if(i & 1) {
int q = (256*60*HUE_DEGREE*v - h*s*v + 60*HUE_DEGREE*s*v*i) / (256*60*HUE_DEGREE);
switch(i) {
case 1: r = q; g = v; b = p; break;
case 3: r = p; g = q; b = v; break;
case 5: r = v; g = p; b = q; break;
}
} else {
int t = (256*60*HUE_DEGREE*v + h*s*v - 60*HUE_DEGREE*s*v*(i+1)) / (256*60*HUE_DEGREE);
switch(i) {
case 0: r = v; g = t; b = p; break;
case 2: r = p; g = v; b = t; break;
case 4: r = t; g = p; b = v; break;
}
}
}
return RGB(r, g, b);
}
#ifdef TEST
#include <stdio.h>
#define DIFF(a,b) ((a) >= (b) ? (a) - (b) : (b) - (a))
int
main(int argc, char** argv)
{
int r0, g0, b0;
hsv_t hsv;
int r1, g1, b1;
int ok = 0, fuzzy = 0, ko = 0, total;
for(r0 = 0; r0 < 256; r0++) {
for(g0 = 0; g0 < 256; g0++) {
for(b0 = 0; b0 < 256; b0++) {
COLORREF tmp;
rgb2hsv(RGB(r0,g0,b0), &hsv);
tmp = hsv2rgb(&hsv);
r1 = GetRValue(tmp);
g1 = GetGValue(tmp);
b1 = GetBValue(tmp);
if(r0 == r1 && b0 == b1 && g0 == g1)
ok++;
else if(DIFF(r0,r1) <= 1 && DIFF(b0,b1) <= 1 && DIFF(g0,g1) <= 1)
fuzzy++;
else
ko++;
}
}
}
total = ok + fuzzy + ko;
printf("Test results:\n");
printf(" * exact matches: %8d (%5.2f%%)\n", ok, (100.0 * ok) / total);
printf(" * fuzzy matches: %8d (%5.2f%%)\n", fuzzy, (100.0 * fuzzy) / total);
printf(" * mismatches: %8d (%5.2f%%)\n", ko, (100.0 * ko) / total);
return (ko == 0 ? 0 : 1);
}
#endif /* TEST */
/*
* RGB <--> HSV conversion in integer arithmetics, to be used on Windows.
* Copyright (c) 2013 Martin Mitas
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#ifndef HSV_H
#define HSV_H
#include <windows.h>
#define HUE_DEGREE 512
typedef struct hsv_tag hsv_t;
struct hsv_tag {
int hue; /* 0 ... (360*HUE_DEGREE - 1) */
BYTE saturation; /* 0 ... 255 */
BYTE value; /* 0 ... 255 */
};
void rgb2hsv(COLORREF rgb, hsv_t* hsv);
COLORREF hsv2rgb(hsv_t* hsv);
#endif /* HSV_H */
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