130 lines
3.5 KiB
GLSL
130 lines
3.5 KiB
GLSL
/*
|
|
[configuration]
|
|
|
|
[OptionRangeFloat]
|
|
GUIName = Amplificiation
|
|
OptionName = AMPLIFICATION
|
|
MinValue = 1.0
|
|
MaxValue = 6.0
|
|
StepAmount = 0.25
|
|
DefaultValue = 2.5
|
|
|
|
[/configuration]
|
|
*/
|
|
|
|
// ICtCP Colorspace as defined by Dolby here:
|
|
// https://professional.dolby.com/siteassets/pdfs/ictcp_dolbywhitepaper_v071.pdf
|
|
|
|
/***** Transfer Function *****/
|
|
|
|
const float a = 0.17883277;
|
|
const float b = 1.0 - 4.0 * a;
|
|
const float c = 0.5 - a * log(4.0 * a);
|
|
|
|
float HLG_f(float x)
|
|
{
|
|
if (x < 0.0) {
|
|
return 0.0;
|
|
}
|
|
|
|
else if (x < 1.0 / 12.0) {
|
|
return sqrt(3.0 * x);
|
|
}
|
|
|
|
return a * log(12.0 * x - b) + c;
|
|
}
|
|
|
|
float HLG_inv_f(float x)
|
|
{
|
|
if (x < 0.0) {
|
|
return 0.0;
|
|
}
|
|
|
|
else if (x < 1.0 / 2.0) {
|
|
return x * x / 3.0;
|
|
}
|
|
|
|
return (exp((x - c) / a) + b) / 12.0;
|
|
}
|
|
|
|
float4 HLG(float4 lms)
|
|
{
|
|
return float4(HLG_f(lms.x), HLG_f(lms.y), HLG_f(lms.z), lms.w);
|
|
}
|
|
|
|
float4 HLG_inv(float4 lms)
|
|
{
|
|
return float4(HLG_inv_f(lms.x), HLG_inv_f(lms.y), HLG_inv_f(lms.z), lms.w);
|
|
}
|
|
|
|
/***** Linear <--> ICtCp *****/
|
|
|
|
const mat4 RGBtoLMS = mat4(
|
|
1688.0, 683.0, 99.0, 0.0,
|
|
2146.0, 2951.0, 309.0, 0.0,
|
|
262.0, 462.0, 3688.0, 0.0,
|
|
0.0, 0.0, 0.0, 4096.0)
|
|
/ 4096.0;
|
|
|
|
const mat4 LMStoICtCp = mat4(
|
|
+2048.0, +3625.0, +9500.0, 0.0,
|
|
+2048.0, -7465.0, -9212.0, 0.0,
|
|
+0.0, +3840.0, -288.0, 0.0,
|
|
+0.0, +0.0, +0.0, 4096.0)
|
|
/ 4096.0;
|
|
|
|
float4 LinearRGBToICtCP(float4 c)
|
|
{
|
|
return LMStoICtCp * HLG(RGBtoLMS * c);
|
|
}
|
|
|
|
/***** ICtCp <--> Linear *****/
|
|
|
|
mat4 ICtCptoLMS = inverse(LMStoICtCp);
|
|
mat4 LMStoRGB = inverse(RGBtoLMS);
|
|
|
|
float4 ICtCpToLinearRGB(float4 c)
|
|
{
|
|
return LMStoRGB * HLG_inv(ICtCptoLMS * c);
|
|
}
|
|
|
|
void main()
|
|
{
|
|
float4 color = Sample();
|
|
|
|
// Nothing to do here, we are in SDR
|
|
if (!OptionEnabled(hdr_output) || !OptionEnabled(linear_space_output)) {
|
|
SetOutput(color);
|
|
return;
|
|
}
|
|
|
|
// Renormalize Color to be in [0.0 - 1.0] SDR Space. We will revert this later.
|
|
const float hdr_paper_white = hdr_paper_white_nits / hdr_sdr_white_nits;
|
|
color.rgb /= hdr_paper_white;
|
|
|
|
// Convert Color to Perceptual Color Space. This will allow us to do perceptual
|
|
// scaling while also being able to use the luminance channel.
|
|
float4 ictcp_color = LinearRGBToICtCP(color);
|
|
|
|
// Scale the color in perceptual space depending on the percieved luminance.
|
|
//
|
|
// At low luminances, ~0.0, pow(AMPLIFICATION, ~0.0) ~= 1.0, so the
|
|
// color will appear to be unchanged. This is important as we don't want to
|
|
// over expose dark colors which would not have otherwise been seen.
|
|
//
|
|
// At high luminances, ~1.0, pow(AMPLIFICATION, ~1.0) ~= AMPLIFICATION,
|
|
// which is equivilant to scaling the color by AMPLIFICATION. This is
|
|
// important as we want to get the most out of the display, and we want to
|
|
// get bright colors to hit their target brightness.
|
|
//
|
|
// For more information, see this desmos demonstrating this scaling process:
|
|
// https://www.desmos.com/calculator/syjyrjsj5c
|
|
float exposure = length(ictcp_color.xyz);
|
|
ictcp_color *= pow(HLG_f(AMPLIFICATION), exposure);
|
|
|
|
// Convert back to Linear RGB and output the color to the display.
|
|
// We use hdr_paper_white to renormalize the color to the comfortable
|
|
// SDR viewing range.
|
|
SetOutput(hdr_paper_white * ICtCpToLinearRGB(ictcp_color));
|
|
}
|