neutral.glsl

// Khronos PBR Neutral Tone Mapper
// https://github.com/KhronosGroup/ToneMapping/tree/main/PBR_Neutral

// Input color is non-negative and resides in the Linear Rec. 709 color space.
// Output color is also Linear Rec. 709, but in the [0, 1] range.
vec3 neutral(vec3 color) {
  const float startCompression = 0.8 - 0.04;
  const float desaturation = 0.15;

  float x = min(color.r, min(color.g, color.b));
  float offset = x < 0.08 ? x - 6.25 * x * x : 0.04;
  color -= offset;

  float peak = max(color.r, max(color.g, color.b));
  if (peak < startCompression) return color;

  const float d = 1.0 - startCompression;
  float newPeak = 1.0 - d * d / (peak + d - startCompression);
  color *= newPeak / peak;

  float g = 1.0 - 1.0 / (desaturation * (peak - newPeak) + 1.0);
  return mix(color, vec3(newPeak), g);
}

#pragma glslify: export(neutral)