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DoViLutGen: canoncial 2020->709 conversion
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@erazortt
erazortt committed Mar 5, 2024
1 parent b94bd40 commit 4267b44
Showing 1 changed file with 115 additions and 43 deletions.
158 changes: 115 additions & 43 deletions DoViBaker/DoViLutGen.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -10,17 +10,17 @@ double EOTFpq(double ep)
static constexpr double c2 = 2413.0 / 4096 * 32;
static constexpr double c1 = c3 - c2 + 1;

const double epower = pow(ep, 1 / m2);
const double epower = std::pow(ep, 1 / m2);
const double num = std::max(epower - c1, 0.0);
const double denom = c2 - c3 * epower;
return pow(num / denom, 1 / m1);
return std::pow(num / denom, 1 / m1);
}

double OOTFhlgInv(double fd, double yd)
{
if (yd > 0) {
static constexpr double power = (1 - 1.2) / 1.2;
return fd * pow(yd, power);
return fd * std::pow(yd, power);
}
return 0;
}
Expand Down Expand Up @@ -90,7 +90,7 @@ double hlg2sdr(double x, double kS, double m1Factor) {
double p1 = 1;

// calculate the maximal m1 such that the curvature of p(t) never becomes positive for any t, especially not for t=1
// p0*h00_2(1)+m0*h10_2(1)+p1*h01_2(1)+m1_max*h11_2(1)=0 <=> p0*h00_2(1)+m0*h10_2(1)+p1*h01_2(1)=-m1_max*h11_2(1)
// p_2(t)=0 <=> p0*h00_2(1)+m0*h10_2(1)+p1*h01_2(1)+m1_max*h11_2(1)=0 <=> p0*h00_2(1)+m0*h10_2(1)+p1*h01_2(1)=-m1_max*h11_2(1)
// => p0*6+m0*2-p1*6=-4*m1_max <=> m1_max=-(p0*6+m0*2-p1*6)/4
double m1max = -(p0*6+m0*2-p1*6)/4;
double m1 = m1Factor * m1max;
Expand All @@ -103,10 +103,6 @@ double hlg2sdr(double x, double kS, double m1Factor) {
return x * matchHlg2Sdr(x);
}

bool outOfRange(double r, double g, double b) {
return b < 0 || b > 1 || g < 0 || g > 1 || r < 0 || r > 1;
}

void xyzFromRgb2020(double& x, double& y, double& z, double rl, double gl, double bl) {
x = 0.636958048 * rl + 0.144616904 * gl + 0.168880975 * bl;
y = 0.262700212 * rl + 0.677998072 * gl + 0.059301716 * bl;
Expand Down Expand Up @@ -141,9 +137,9 @@ void XYZfromLms(double& x, double& y, double& z, double l, double m, double s) {
}

void labFromLms(double& L, double& a, double& b, double l, double m, double s) {
l = std::pow(l, 0.33333333);
m = std::pow(m, 0.33333333);
s = std::pow(s, 0.33333333);
l = std::pow(l, 0.3333333333);
m = std::pow(m, 0.3333333333);
s = std::pow(s, 0.3333333333);
L = 0.2104542553 * l + 0.7936177850 * m - 0.0040720468 * s;
a = 1.9779984951 * l - 2.4285922050 * m + 0.4505937099 * s;
b = 0.0259040371 * l + 0.7827717662 * m - 0.8086757660 * s;
Expand Down Expand Up @@ -192,41 +188,93 @@ void convert2020To709(double& rl, double& gl, double& bl) {
rgb709FromXYZ(rl, gl, bl, x, y, z);
}

void clip2020Chroma(double& rl, double& gl, double& bl) {
// slightly decreases the chroma such that the shrunken BT.2020 gamut tangentialy hits the BT.709 gamut
// this first happens along the blue edge of BT.709 (0,0,b)
void reduceChroma(double& rl, double& gl, double& bl) {
double L, a, b;
labFromRgb2020(L, a, b, rl, gl, bl);
double f=0.5;
for (int d = 4; d < 16385; d *= 2) {
rgb2020fromLab(rl, gl, bl, L, a*f, b*f);
if (outOfRange(rl, gl, bl)) {
f -= 1.0 / d;
}
else {
f += 1.0 / d;
}
}
double f = 0.9418;
rgb2020fromLab(rl, gl, bl, L, a * f, b * f);
}

void clip709Chroma(double& rl, double& gl, double& bl) {
double L, a, b;
labFromRgb709(L, a, b, rl, gl, bl);
double f = 0.5;
for (int d = 4; d < 8193; d *= 2) {
rgb709fromLab(rl, gl, bl, L, a * f, b * f);
if (outOfRange(rl, gl, bl)) {
typedef void (*rgbFromLab)(double& rl, double& gl, double& bl, double L, double a, double b);
typedef void (*labFromRgb)(double& L, double& a, double& b, double rl, double gl, double bl);

bool outOfRange(double r, double g, double b) {
return b > 1. || g > 1. || r > 1.;
}

void findInRangeLab(double& Li, double& Ai, double& Bi, double ri, double gi, double bi, double sensL, double sensA, double sensB, rgbFromLab rgbFromLabFunc) {
double f = 1;
for (int d = 2; d < (1 << 29) + 1; d *= 2) {
if (outOfRange(ri, gi, bi)) {
f -= 1.0 / d;
}
else {
f += 1.0 / d;
}
double facL = 1 - sensL * (1 - f);
double facA = 1 - sensA * (1 - f);
double facB = 1 - sensB * (1 - f);
rgbFromLabFunc(ri, gi, bi, Li * facL, Ai * facA, Bi * facB);
}

double facL = 1 - sensL * (1 - f);
double facA = 1 - sensA * (1 - f);
double facB = 1 - sensB * (1 - f);
Li *= facL;
Ai *= facA;
Bi *= facB;
}

void reduceChroma(double& rl, double& gl, double& bl) {
double L, a, b;
labFromRgb2020(L, a, b, rl, gl, bl);
double f = 0.9418;
rgb2020fromLab(rl, gl, bl, L, a * f, b * f);
void clipToPoint(double& ri, double& gi, double& bi, rgbFromLab rgbFromLabFunc, labFromRgb labFromRgbFunc) {
// changes the chroma of an out-of-range color such that it becomes in-range, while leaving lightness and hue constant.
// unfortunately this does not produce good results, the approch varying also lightness the way to go. See function below.

double Li, Ai, Bi;
labFromRgbFunc(Li, Ai, Bi, ri, gi, bi);

double Lo = Li;
double Ao = Ai;
double Bo = Bi;
findInRangeLab(Lo, Ao, Bo, ri, gi, bi, 0, 1, 1, rgbFromLabFunc);

rgbFromLabFunc(ri, gi, bi, Lo, Ao, Bo);
}

void clipToTangentLine(double& ri, double& gi, double& bi, rgbFromLab rgbFromLabFunc, labFromRgb labFromRgbFunc) {
// finds the most similar looking in-gamut color for an out-of-range color, while leaving hue constant.

double Li, Ai, Bi;
labFromRgbFunc(Li, Ai, Bi, ri, gi, bi);

//first in-range point on the surface of the target gamut
double L1 = Li;
double A1 = Ai;
double B1 = Bi;
findInRangeLab(L1, A1, B1, ri, gi, bi, 0, 1, 1, rgbFromLabFunc);

//second in-range point on the surface of the target gamut
double L2 = Li;
double A2 = Ai;
double B2 = Bi;
findInRangeLab(L2, A2, B2, ri, gi, bi, 1, 1, 1, rgbFromLabFunc);

//calculate normal vector from given out-of-range point to the line connecting the two in-range points
//the intersection point of that line to the normal is the nearest in-range point
double r = (A1 * A1 + A2 * Ai - A1 * (A2 + Ai) + (B1 - B2) * (B1 - Bi) + (L1 - L2) * (L1 - Li)) / ((A1 - A2) * (A1 - A2) + (B1 - B2) * (B1 - B2) + (L1 - L2) * (L1 - L2));
double Lo = L1 + (L2 - L1) * r;
double Ao = A1 + (A2 - A1) * r;
double Bo = B1 + (B2 - B1) * r;

rgbFromLabFunc(ri, gi, bi, Lo, Ao, Bo);
}

void softClip709(double& rl, double& gl, double& bl) {
clipToTangentLine(rl, gl, bl, rgb709fromLab, labFromRgb709);
}
void softClip2020(double& rl, double& gl, double& bl) {
clipToTangentLine(rl, gl, bl, rgb2020fromLab, labFromRgb2020);
}

void showBestLutSizes() {
Expand All @@ -247,6 +295,15 @@ void warnAboutLutSize() {
printf("\n");
}

void selfTest() {
{
double r = 1.25;
double g = 0;
double b = 0;
softClip2020(r, g, b);
}
}

#ifdef DOVI_LUTGEN
int main(int argc, char* argv[])
{
Expand Down Expand Up @@ -374,16 +431,21 @@ int main(int argc, char* argv[])
double bs = OOTFhlgInv(bd, yd);

/*if (outOfRange(rs, gs, bs)) {
clip2020Chroma(rs, gs, bs);
softClip2020(rs, gs, bs);
softClip2020(rs, gs, bs);
}*/

if (rs < 0)rs = 0;
if (gs < 0)gs = 0;
if (bs < 0)bs = 0;

double rg = OETFhlg(rs);
double gg = OETFhlg(gs);
double bg = OETFhlg(bs);

bg = std::clamp(bg, 0.0, 1.0);
gg = std::clamp(gg, 0.0, 1.0);
rg = std::clamp(rg, 0.0, 1.0);
if (rg > 1)rg = 1;
if (gg > 1)gg = 1;
if (bg > 1)bg = 1;

if (sdr) {
rg = hlg2sdr(rg, sdrKneeStart, sdrKneeEndTangentFactor);
Expand All @@ -394,19 +456,29 @@ int main(int argc, char* argv[])
double rl = EOTFsdr(rg);
double gl = EOTFsdr(gg);
double bl = EOTFsdr(bg);
reduceChroma(rl, gl, bl);
//reduceChroma(rl, gl, bl);
convert2020To709(rl, gl, bl);

if (rl < 0)rl = 0;
if (gl < 0)gl = 0;
if (bl < 0)bl = 0;

/*if (outOfRange(rl, gl, bl)) {
clip709Chroma(rl, gl, bl);
softClip709(rl, gl, bl);
softClip709(rl, gl, bl);
if (rl < 0)rl = 0;
if (gl < 0)gl = 0;
if (bl < 0)bl = 0;
}*/

rg = OETFsdr(rl);
gg = OETFsdr(gl);
bg = OETFsdr(bl);
}

bg = std::clamp(bg, 0.0, 1.0);
gg = std::clamp(gg, 0.0, 1.0);
rg = std::clamp(rg, 0.0, 1.0);
if (rg > 1)rg = 1;
if (gg > 1)gg = 1;
if (bg > 1)bg = 1;
}

fsCube << rg << " " << gg << " " << bg << std::endl;
Expand Down

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