Re: [Algorithms] RGB to XYZ conversion

[Jon W. <hp...@mi...>]

Willem H. de Boer wrote:
> But, this doesn't take away from the fact that the interpolation
> can choose colours in between (i.e. for t in [0,1]) that are
> in some ways 'wrong' or at least counterintuitive to what
> we would expect - which is what Jon points out. This is
> a result of the way YCoCg maps out in colour space.
>   

Note: that "Jon" was a different Jon than me :-)

It actually does mean that all the interpolated colors will be the same, 
because for _any_ "a" and "b" (interpolation values, equal to t and 
1-t), a*x + b*y equals R'(aRx +bRy), through mathematic equality. So, 
no, there would not be interpolation artifacts based on the math being 
in a different space. This is because the two spaces are linearly 
equivalent. You don't get interpolation differences until you go to a 
non-equivalent space, such as HSV, or a space with a different gamma.

The interpolation of DXT compression, though, is somewhat quantized, and 
will generally result in a slight green/purple banding in RGB. That 
quantization may cause a different color banding effect in the Y Co Cg 
space, because quantization is not a linearly independent operation.

Sincerely,

jw