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float ycbcrCoeffs[3] = { .299, .587, .114 };
/* default coding range is CCIR Rec 601-1 with no headroom/footroom */
unsigned long refBlackWhite[6] = { 0, 255, 128, 255, 128, 255 };
#define LumaRed ycbcrCoeffs[0]
#define LumaGreen ycbcrCoeffs[1]
#define LumaBlue ycbcrCoeffs[2]
long eRtotal = 0;
long eGtotal = 0;
long eBtotal = 0;
long preveRtotal = 0;
long preveGtotal = 0;
long preveBtotal = 0;
unsigned long AbseRtotal = 0;
unsigned long AbseGtotal = 0;
unsigned long AbseBtotal = 0;
unsigned long eCodes = 0;
unsigned long preveCodes = 0;
unsigned long eBits = 0;
unsigned long preveBits = 0;
static void setupLumaTables();
static int abs(int v) { return (v < 0 ? -v : v); }
static double pct(int v,double range) { return (v*100. / range); }
static void check(int R, int G, int B);
float D1, D2;
float D3, D4;
float D5, D6;
int
main(int argc, char** argv)
{
int R, G, B;
if (argc > 1) {
refBlackWhite[0] = 16;
refBlackWhite[1] = 235;
refBlackWhite[2] = 128;
refBlackWhite[3] = 240;
refBlackWhite[4] = 128;
refBlackWhite[5] = 240;
}
D3 = 2 - 2*LumaRed;
D4 = 2 - 2*LumaBlue;
D1 = 1. / D3;
D2 = 1. / D4;
D5 = D3*LumaRed / LumaGreen;
D6 = D4*LumaBlue / LumaGreen;
setupLumaTables();
for (R = 0; R < 256; R++) {
for (G = 0; G < 256; G++)
for (B = 0; B < 256; B++)
check(R, G, B);
printf("[%3u] c %u/%u b %u/%u (R %u/%d/%u G %u/%d/%u B %u/%d/%u)\n"
, R
, eCodes - preveCodes, eCodes
, eBits - preveBits, eBits
, abs(AbseRtotal - preveRtotal), eRtotal , AbseRtotal
, abs(AbseGtotal - preveGtotal), eGtotal , AbseGtotal
, abs(AbseBtotal - preveBtotal), eBtotal , AbseBtotal
);
preveRtotal = AbseRtotal;
preveGtotal = AbseGtotal;
preveBtotal = AbseBtotal;
preveCodes = eCodes;
preveBits = eBits;
}
printf("%u total codes\n", 256*256*256);
printf("total error: %u codes %u bits (R %d/%u G %d/%u B %d/%u)\n"
, eCodes
, eBits
, eRtotal , AbseRtotal
, eGtotal , AbseGtotal
, eBtotal , AbseBtotal
);
return (0);
}
float *lumaRed;
float *lumaGreen;
float *lumaBlue;
static float*
setupLuma(float c)
{
float *v = (float *)_TIFFmalloc(256 * sizeof (float));
int i;
for (i = 0; i < 256; i++)
v[i] = c * i;
return (v);
}
static void
setupLumaTables(void)
{
lumaRed = setupLuma(LumaRed);
lumaGreen = setupLuma(LumaGreen);
lumaBlue = setupLuma(LumaBlue);
}
static unsigned
V2Code(float f, unsigned long RB, unsigned long RW, int CR)
{
unsigned int c = (unsigned int)((((f)*(RW-RB)/CR)+RB)+.5);
return (c > 255 ? 255 : c);
}
#define Code2V(c, RB, RW, CR) ((((c)-(int)RB)*(float)CR)/(float)(RW-RB))
#define CLAMP(f,min,max) \
(int)((f)+.5 < (min) ? (min) : (f)+.5 > (max) ? (max) : (f)+.5)
static
void
check(int R, int G, int B)
{
float Y, Cb, Cr;
int iY, iCb, iCr;
float rY, rCb, rCr;
float rR, rG, rB;
int eR, eG, eB;
Y = lumaRed[R] + lumaGreen[G] + lumaBlue[B];
Cb = (B - Y)*D2;
Cr = (R - Y)*D1;
iY = V2Code(Y, refBlackWhite[0], refBlackWhite[1], 255);
iCb = V2Code(Cb, refBlackWhite[2], refBlackWhite[3], 127);
iCr = V2Code(Cr, refBlackWhite[4], refBlackWhite[5], 127);
rCb = Code2V(iCb, refBlackWhite[2], refBlackWhite[3], 127);
rCr = Code2V(iCr, refBlackWhite[4], refBlackWhite[5], 127);
rY = Code2V(iY, refBlackWhite[0], refBlackWhite[1], 255);
rR = rY + rCr*D3;
rB = rY + rCb*D4;
rG = rY - rCb*D6 - rCr*D5;
eR = R - CLAMP(rR,0,255);
eG = G - CLAMP(rG,0,255);
eB = B - CLAMP(rB,0,255);
if (abs(eR) > 1 || abs(eG) > 1 || abs(eB) > 1) {
printf("R %u G %u B %u", R, G, B);
printf(" Y %g Cb %g Cr %g", Y, Cb, Cr);
printf(" iY %u iCb %u iCr %u", iY, iCb, iCr);
printf("\n -> Y %g Cb %g Cr %g", rY, rCb, rCr);
printf(" R %g (%u) G %g (%u) B %g (%u) E=[%d %d %d])\n"
, rR, CLAMP(rR,0,255)
, rG, CLAMP(rG,0,255)
, rB, CLAMP(rB,0,255)
, eR, eG, eB
);
}
eRtotal += eR;
eGtotal += eG;
eBtotal += eB;
AbseRtotal += abs(eR);
AbseGtotal += abs(eG);
AbseBtotal += abs(eB);
if (eR | eG | eB)
eCodes++;
eBits += abs(eR) + abs(eG) + abs(eB);
}
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