Re: [Algorithms] RGB to XYZ conversion

[Jon O. <jon...@gm...>]

Hi Jon,

So, thats interesting then that the bilinear interpolation of RGB colors
have artifacts. As soon as I get a chance I'll take a closer look at our
assets and both in straight up RGB and DXT5 to verify. After reading your
e-mail, I went over to Jan Pal (our local YCoCg expert) to ask him about
this very interpolation problem and he swears that the interpolation in
YCoCg is not the same as interpolation in RGB. We were looking at this about
6 months ago now, but we very well could have made a mistake.

Best,
Jon Olick

On Thu, Apr 24, 2008 at 4:54 PM, Jon Watte <hp...@mi...> wrote:

> 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
>
>
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