MelaninColor.osl

// Melanin Color Generator OSL node based on Weta's Melanin research paper.
// This was made for Redshift 3D, by Saul Espinosa v.2.1
// Modified : 3/15/2021 - Added ACEScg Output Support
// outColor should be input into the Transmission, Internal Reflection inputs of the rsHair and Diffuse if used.
// This file is licensed under Apache 2.0 license


shader MelaninColor
[[  string help = "Generates Melanin Output Colors",
    string label = "Melanin Color" ]]
(
float melanin = 0.5 [[float min = 0, float max = 1, string label = "Melanin"]],
color dyeColor = 1 [[string label = "Dye Color"]],
float redness = 0 [[float min = 0, float max = 1, string label = "Melanin Redness"]],
float dyeMix = 0 [[float min = 0, float max = 1, string label = "Dye Mix"]],
int convToAces = 0 [[ string widget = "checkBox", string label = "ACES", int connectable = 0 ]],	
 
output color outColor = 0
)
{
// ACES Transform
	matrix srgbToAcesAP1 = {
 	0.6131, 0.0701, 0.0206, 0,
	0.3395, 0.9164, 0.1096, 0,
	0.0474, 0.0135, 0.8698, 0,
	0, 0, 0, 1 };	

float w = max( pow(melanin, 2.0) * 33.0, 0.02);
	color pheomelanin = exp(w * -vector(0.187, 0.4, 1.05));
	color eumelanin = exp(w * -vector(0.419, 0.697, 1.37));
	
	
	color mel_out = mix(mix(eumelanin, pheomelanin, redness), dyeColor, dyeMix);
	float sR = mel_out[0];
	float sG = mel_out[1];
	float sB = mel_out[2];
	
	if (convToAces == 1){
		outColor = transform(srgbToAcesAP1, vector(sR, sG, sB));
	}
	else {
		outColor = mel_out;
	}
}