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@djg djg/test3.cpp
Created Jul 8, 2010

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// Another test. RGB->YCoCg conversion. Think I discovered a problem with negative
// values being returned on RGB->YCoCg->RGB.
#include <stdio.h>
struct IVect { int x, y, z; };
/*
* [Y ] = [ 1/4 1/2 1/4][R] R, G, B = [0..255] => Y = [0..255], Co, Cg = [-128..127]
* [Co] [ 1/2 0 -1/2][G]
* [Cg] [-1/4 1/2 -1/4][B]
*/
IVect
RGB_to_YCoCg(const IVect& rgb)
{
IVect ycocg;
// int s = (rgb.x >> 2) + (rgb.z >> 2);
int s = (rgb.x + rgb.z) >> 2;
int t = rgb.y >> 1;
ycocg.x = t + s;
ycocg.z = t - s;
// ycocg.y = (rgb.x >> 1) - (rgb.z >> 1);
ycocg.y = (rgb.x - rgb.z) >> 1;
return ycocg;
}
IVect
YCoCg_to_RGB(const IVect& ycocg)
{
IVect rgb;
int t = ycocg.x - ycocg.z;
rgb.x = t + ycocg.y;
rgb.y = ycocg.x + ycocg.z;
rgb.z = t - ycocg.y;
return rgb;
}
int
main()
{
IVect colors[] =
{
{ 0, 0, 0 },
{ 255, 0, 0 },
{ 0, 255, 0 },
{ 255, 255, 0 },
{ 0, 0, 255 },
{ 255, 0, 255 },
{ 0, 255, 255 },
{ 255, 255, 255 },
{ 255, 127, 0 },
{ 127, 255, 0 },
{ 255, 0, 127 },
{ 127, 0, 255 },
{ 0, 255, 127 },
{ 0, 127, 255 },
};
for (int i = 0; i < 14; ++i)
{
const IVect t1 = RGB_to_YCoCg(colors[i]);
const IVect t2 = YCoCg_to_RGB(t1);
printf("{R=%3d, G=%3d, B=%3d} => {Y=%3d, Co=%4d, Cg=%4d} => {R=%3d, G=%3d, B=%3d}\n",
colors[i].x, colors[i].y, colors[i].z, t1.x, t1.y, t1.z, t2.x, t2.y, t2.z);
}
return 0;
}
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