Dart ITU-R BT.2446 Conversion Method C, From HDR Toys glsl

tonemap_2446c.dart

// ---------------------------------------------------------------------------------------------------------------------------------------

// ITU-R BT.2446 Conversion Method C
// https://www.itu.int/pub/R-REP-BT.2446

//!HOOK OUTPUT
//!BIND HOOKED
//!DESC tone mapping (bt.2446c)

Vector3 RGB_to_XYZ(Vector3 RGB) {
  Matrix3 M = Matrix3(
      0.6369580483012914,
      0.14461690358620832,
      0.1688809751641721,
      0.2627002120112671,
      0.6779980715188708,
      0.05930171646986196,
      0.000000000000000,
      0.028072693049087428,
      1.060985057710791);
  return RGB..applyMatrix3(M);
}

Vector3 XYZ_to_RGB(Vector3 XYZ) {
  Matrix3 M = Matrix3(
      1.716651187971268,
      -0.355670783776392,
      -0.253366281373660,
      -0.666684351832489,
      1.616481236634939,
      0.0157685458139111,
      0.017639857445311,
      -0.042770613257809,
      0.942103121235474);
  return XYZ..applyMatrix3(M);
}

Vector3 XYZ_to_xyY(Vector3 XYZ) {
  double X = XYZ.x;
  double Y = XYZ.y;
  double Z = XYZ.z;

  double divisor = X + Y + Z;
  if (divisor == 0.0) divisor = 1e-6;

  double x = X / divisor;
  double y = Y / divisor;

  return Vector3(x, y, Y);
}

Vector3 xyY_to_XYZ(Vector3 xyY) {
  double x = xyY.x;
  double y = xyY.y;
  double Y = xyY.z;

  double multiplo = Y / max(y, 1e-6);

  double z = 1.0 - x - y;
  double X = x * multiplo;
  double Z = z * multiplo;

  return Vector3(X, Y, Z);
}

const double ip = 0.58535; // linear length
const double k1 = 0.83802; // linear strength
const double k3 = 0.74204; // shoulder strength

double f2(double Y, double k1, double k3, double ip) {
  ip /= k1;
  double k2 = (k1 * ip) * (1.0 - k3);
  double k4 = (k1 * ip) - (k2 * log(1.0 - k3));
  return Y < ip ? Y * k1 : log((Y / ip) - k3) * k2 + k4;
}

double curve2(double x) {
  const double over_white = 1019.0 / 940.0; // 109% range (super-whites)
  return f2(x, k1, k3, ip) / over_white;
}

Vector4 hook3(double r, double g, double b) {
  Vector4 color = Vector4(r, g, b, 1.0);

  color.rgb = RGB_to_XYZ(color.rgb);
  color.rgb = XYZ_to_xyY(color.rgb);
  // color.z = curve2(color.z);
  color.rgb = xyY_to_XYZ(color.rgb);
  color.rgb = XYZ_to_RGB(color.rgb);

  return color;
}

void applyToneMapping2446c(Float32List hdrImage) {
  for (int i = 0; i < hdrImage.length; i += 3) {
    final color = hook3(hdrImage[i], hdrImage[i + 1], hdrImage[i + 2]);
    hdrImage[i] = color.x;
    hdrImage[i + 1] = color.y;
    hdrImage[i + 2] = color.z;
  }
}