fromXyzInViewingConditions static method

Cam16 fromXyzInViewingConditions(double x, double y, double z, ViewingConditions viewingConditions,)

Given color expressed in XYZ and viewed in viewingConditions, convert to CAM16.

Implementation

static Cam16 fromXyzInViewingConditions(double x, double y, double z, ViewingConditions viewingConditions) {
  // Transform XYZ to 'cone'/'rgb' responses

  final double rC = 0.401288 * x + 0.650173 * y - 0.051461 * z;
  final double gC = -0.250268 * x + 1.204414 * y + 0.045854 * z;
  final double bC = -0.002079 * x + 0.048952 * y + 0.953127 * z;

  // Discount illuminant
  final double rD = viewingConditions.rgbD[0] * rC;
  final double gD = viewingConditions.rgbD[1] * gC;
  final double bD = viewingConditions.rgbD[2] * bC;

  // chromatic adaptation
  final double rAF = math.pow(viewingConditions.fl * rD.abs() / 100.0, 0.42).toDouble();
  final double gAF = math.pow(viewingConditions.fl * gD.abs() / 100.0, 0.42).toDouble();
  final double bAF = math.pow(viewingConditions.fl * bD.abs() / 100.0, 0.42).toDouble();
  final double rA = MathUtils.signum(rD) * 400.0 * rAF / (rAF + 27.13);
  final double gA = MathUtils.signum(gD) * 400.0 * gAF / (gAF + 27.13);
  final double bA = MathUtils.signum(bD) * 400.0 * bAF / (bAF + 27.13);

  // redness-greenness
  final double a = (11.0 * rA + -12.0 * gA + bA) / 11.0;
  // yellowness-blueness
  final double b = (rA + gA - 2.0 * bA) / 9.0;

  // auxiliary components
  final double u = (20.0 * rA + 20.0 * gA + 21.0 * bA) / 20.0;
  final double p2 = (40.0 * rA + 20.0 * gA + bA) / 20.0;

  // hue
  final double atan2 = math.atan2(b, a);
  final double atanDegrees = atan2 * 180.0 / math.pi;
  final double hue = MathUtils.sanitizeDegreesDouble(atanDegrees);
  final double hueRadians = hue * math.pi / 180.0;
  assert(hue >= 0 && hue < 360, 'hue was really $hue');

  // achromatic response to color
  final double ac = p2 * viewingConditions.nbb;

  // CAM16 lightness and brightness
  final double J = 100.0 * math.pow(ac / viewingConditions.aw, viewingConditions.c * viewingConditions.z);
  final double Q =
      (4.0 / viewingConditions.c) * math.sqrt(J / 100.0) * (viewingConditions.aw + 4.0) * (viewingConditions.fLRoot);

  final double huePrime = (hue < 20.14) ? hue + 360 : hue;
  final double eHue = (1.0 / 4.0) * (math.cos(huePrime * math.pi / 180.0 + 2.0) + 3.8);
  final double p1 = 50000.0 / 13.0 * eHue * viewingConditions.nC * viewingConditions.ncb;
  final double t = p1 * math.sqrt(a * a + b * b) / (u + 0.305);
  final num alpha =
      math.pow(t, 0.9) * math.pow(1.64 - math.pow(0.29, viewingConditions.backgroundYTowhitePointY), 0.73);
  // CAM16 chroma, colorfulness, chroma
  final double C = alpha * math.sqrt(J / 100.0);
  final double M = C * viewingConditions.fLRoot;
  final double s = 50.0 * math.sqrt((alpha * viewingConditions.c) / (viewingConditions.aw + 4.0));

  // CAM16-UCS components
  final double jstar = (1.0 + 100.0 * 0.007) * J / (1.0 + 0.007 * J);
  final double mstar = math.log(1.0 + 0.0228 * M) / 0.0228;
  final double astar = mstar * math.cos(hueRadians);
  final double bstar = mstar * math.sin(hueRadians);
  return Cam16(hue, C, J, Q, M, s, jstar, astar, bstar);
}