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

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

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

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

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

  // hue
  final atan2 = math.atan2(b, a);
  final atanDegrees = atan2 * 180.0 / math.pi;
  final hue = atanDegrees < 0
      ? atanDegrees + 360.0
      : atanDegrees >= 360
          ? atanDegrees - 360
          : atanDegrees;
  final hueRadians = hue * math.pi / 180.0;
  assert(hue >= 0 && hue < 360, 'hue was really $hue');

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

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

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

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