dng_matrix_3by3 MapWhiteMatrix (const dng_xy_coord &white1,
const dng_xy_coord &white2)
{
// Use the linearized Bradford adaptation matrix.
dng_matrix_3by3 Mb ( 0.8951, 0.2664, -0.1614,
-0.7502, 1.7135, 0.0367,
0.0389, -0.0685, 1.0296);
dng_vector_3 w1 = Mb * XYtoXYZ (white1);
dng_vector_3 w2 = Mb * XYtoXYZ (white2);
// Negative white coordinates are kind of meaningless.
w1 [0] = Max_real64 (w1 [0], 0.0);
w1 [1] = Max_real64 (w1 [1], 0.0);
w1 [2] = Max_real64 (w1 [2], 0.0);
w2 [0] = Max_real64 (w2 [0], 0.0);
w2 [1] = Max_real64 (w2 [1], 0.0);
w2 [2] = Max_real64 (w2 [2], 0.0);
// Limit scaling to something reasonable.
dng_matrix_3by3 A;
A [0] [0] = Pin_real64 (0.1, w1 [0] > 0.0 ? w2 [0] / w1 [0] : 10.0, 10.0);
A [1] [1] = Pin_real64 (0.1, w1 [1] > 0.0 ? w2 [1] / w1 [1] : 10.0, 10.0);
A [2] [2] = Pin_real64 (0.1, w1 [2] > 0.0 ? w2 [2] / w1 [2] : 10.0, 10.0);
dng_matrix_3by3 B = Invert (Mb) * A * Mb;
return B;
}
dng_vector_3 PCStoXYZ ()
{
return XYtoXYZ (PCStoXY ());
}
void dng_color_spec::SetWhiteXY (const dng_xy_coord &white)
{
fWhiteXY = white;
// Deal with monochrome cameras.
if (fChannels == 1)
{
fCameraWhite.SetIdentity (1);
fCameraToPCS = PCStoXYZ ().AsColumn ();
return;
}
// Interpolate an matric values for this white point.
dng_matrix colorMatrix;
dng_matrix forwardMatrix;
dng_matrix reductionMatrix;
dng_matrix cameraCalibration;
colorMatrix = FindXYZtoCamera (fWhiteXY,
&forwardMatrix,
&reductionMatrix,
&cameraCalibration);
// Find the camera white values.
fCameraWhite = colorMatrix * XYtoXYZ (fWhiteXY);
real64 whiteScale = 1.0 / MaxEntry (fCameraWhite);
for (uint32 j = 0; j < fChannels; j++)
{
// We don't support non-positive values for camera neutral values.
fCameraWhite [j] = Pin_real64 (0.001,
whiteScale * fCameraWhite [j],
1.0);
}
// Find PCS to Camera transform. Scale matrix so PCS white can just be
// reached when the first camera channel saturates
fPCStoCamera = colorMatrix * MapWhiteMatrix (PCStoXY (), fWhiteXY);
real64 scale = MaxEntry (fPCStoCamera * PCStoXYZ ());
fPCStoCamera = (1.0 / scale) * fPCStoCamera;
// If we have a forward matrix, then just use that.
if (forwardMatrix.NotEmpty ())
{
dng_matrix individualToReference = Invert (fAnalogBalance * cameraCalibration);
dng_vector refCameraWhite = individualToReference * fCameraWhite;
fCameraToPCS = forwardMatrix *
Invert (refCameraWhite.AsDiagonal ()) *
individualToReference;
}
// Else we need to use the adapt in XYZ method.
else
{
// Invert this PCS to camera matrix. Note that if there are more than three
// camera channels, this inversion is non-unique.
fCameraToPCS = Invert (fPCStoCamera, reductionMatrix);
}
}