Makes an grey-scale image, for alpha-channel use.
The given value (or current color) are used for coordinates
in the color cube. Each resulting pixel is the
distance from this point to the source pixel color,
in the color cube, squared, rightshifted 8 steps:
p = pixel color
o = given color
d = destination pixel
d.red=d.blue=d.green=
((o.red-p.red)²+(o.green-p.green)²+(o.blue-p.blue)²)>>8
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original |
distance² to cyan |
...to purple |
...to yellow |