/// \brief Compute a 3x3 matrix which maps colors from white point white1 to
/// white point white2
///
/// Uses linearized Bradford adaptation matrix to compute a mapping from
/// colors measured with one white point (white1) to another (white2).
public static DNGMatrix3x3 MapWhiteMatrix(DNGxyCoord white1, DNGxyCoord white2)
{
// Use the linearized Bradford adaptation matrix.
DNGMatrix3x3 Mb = new DNGMatrix3x3(0.8951, 0.2664, -0.1614,
-0.7502, 1.7135, 0.0367,
0.0389, -0.0685, 1.0296);
DNGVector w1 = Mb * white1.XYtoXYZ();
DNGVector w2 = Mb * white2.XYtoXYZ();
// Negative white coordinates are kind of meaningless.
w1[0] = Math.Max(w1[0], 0.0);
w1[1] = Math.Max(w1[1], 0.0);
w1[2] = Math.Max(w1[2], 0.0);
w2[0] = Math.Max(w2[0], 0.0);
w2[1] = Math.Max(w2[1], 0.0);
w2[2] = Math.Max(w2[2], 0.0);
// Limit scaling to something reasonable.
DNGMatrix3x3 A = new DNGMatrix3x3();
A[0, 0] = DNGUtils.Pin(0.1, w1[0] > 0.0 ? w2[0] / w1[0] : 10.0, 10.0);
A[1, 1] = DNGUtils.Pin(0.1, w1[1] > 0.0 ? w2[1] / w1[1] : 10.0, 10.0);
A[2, 2] = DNGUtils.Pin(0.1, w1[2] > 0.0 ? w2[2] / w1[2] : 10.0, 10.0);
DNGMatrix3x3 B = new DNGMatrix3x3(Mb.Invert() * A * Mb);
return(B);
}
public DNGVector3 XYtoXYZ()
{
DNGxyCoord temp = new DNGxyCoord(this);
// Restrict xy coord to someplace inside the range of real xy coordinates.
// This prevents math from doing strange things when users specify
// extreme temperature/tint coordinates.
temp.x = DNGUtils.Pin(0.000001, temp.x, 0.999999);
temp.y = DNGUtils.Pin(0.000001, temp.y, 0.999999);
if (temp.x + temp.y > 0.999999)
{
double scale = 0.999999 / (temp.x + temp.y);
temp.x *= scale;
temp.y *= scale;
}
return(new DNGVector3(temp.x / temp.y,
1.0,
(1.0 - temp.x - temp.y) / temp.y));
}
