M = RGBToXYZMatrix(xr, yr, xg, yg, xb, yb, xw, yw)

Build a 3x3 color space conversion (CSC) matrix for converting R,G,B
linear color value vectors into the XYZ color space, by a matrix-vector
multiplication, ie. xyz = M * rgb;

The source color space for the rgb (R,G,B) vector is defined by its
color gamut, which in turn is specified by the 2D CIE-1931 chromaticity
coordinates of the white-point (xw, yw) and the color primaries red,
green and blue (xr, yr), (xg, yg) and (xb, yb).

See also the function XYZToRGBMatrix() for building the inverse matrix
for mapping from XYZ space to a target RGB color space.

This code is based on the mathematical derivations and sample code from
Gernot Hoffmann, from: http://docs-hoffmann.de/ciexyz29082000.pdf

The math is consistent afaics with the one derived by Bruce Lindbloom:

Also with http://www.ryanjuckett.com/programming/rgb-color-space-conversion

This Matlab code delivers the same results as Screen()’s internal C
implementation for color space conversion during movie playback, and was
also spot-checked against publically available reference matrices for the
sRGB color space, e.g., Wikipedia, Matlab / Octave, esp. Bruce Lindbloom:

So there’s some confidence this is not totally wrong ;) - But i’m not a
color scientist, so buyers beware!

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