Quote:
Originally Posted by dr1394 
It's just a rounding issue. The 601 and 709 specifications want you to round up for integers. If you do the floating point math, you'll see that Y = 63 (0x3f), Cb = 102 (0x66) and Cr = 240 (0xf0) converts to R = 235.4406, G = 16.502108 and B = 15.831311. The 16.502108 gets rounded up to 17. Here's the floating point code (for video RGB levels):
http://www.w6rz.net/yuvtorgbcalc.zip
Ron
It's just a rounding issue. The 601 and 709 specifications want you to round up for integers. If you do the floating point math, you'll see that Y = 63 (0x3f), Cb = 102 (0x66) and Cr = 240 (0xf0) converts to R = 235.4406, G = 16.502108 and B = 15.831311. The 16.502108 gets rounded up to 17. Here's the floating point code (for video RGB levels):
Code:
/*
Converts YUV to RGB floating point
*/
#include
#include
#define TRUE 1
#define FALSE 0
/* color space conversion coefficients
* for YCbCr -> RGB mapping
*
* entries are {crv,cbu,cgu,cgv}
*
* crv=(219/224)*(1-cr)/0.5
* cbu=(219/224)*(1-cb)/0.5
* cgu=(219/224)*(cb/cg)*(1-cb)/0.5
* cgv=(219/224)*(cr/cg)*(1-cr)/0.5
*
* where Y=cr*R+cg*G+cb*B (cr+cg+cb=1)
*/
/* ITU-R BT709-5 (2002) coefficients */
/* cg = 0.7152 */
/* cb = 0.0722 */
/* cr = 0.2126 */
int main(int argc, char **argv)
{
int y, cr, cb;
double r, g, b;
if (argc != 4) {
fprintf(stderr, "usage: yuvtorgbcalc \
");
exit(-1);
}
y = atoi(argv[1]);
cb = atoi(argv[2]);
cr = atoi(argv[3]);
r = (double)y + 1.5396482142857 * (double)(cr - 128);
g = (double)y - 0.4576750704098 * (double)(cr - 128) - 0.18314292755273 * (double)(cb - 128);
b = (double)y + 1.814180357142857 * (double)(cb - 128);
printf("R = %f, G = %f, B = %f\
", r, g, b);
return 0;
}
Ron
It amazes me how you have some code for every question I ask.
You don't have the source for a time machine laying around do you? I was thinking I could jump forward a few weeks, ask myself all the questions I have, and then jump back to save us all some time and trouble
