"m@b" <sai### [at] googlemailcom> wrote:

> But I would need some primitives to put the pattern on?

Of course.  A thin box or the union of 2 triangles works well.  A plane if you
just want to have the largest possible palette.

But the idea is that you have a lot of stuff going on after you "extract" the
colors.  Rather than do that, you use the color values directly to select a
pigment, by using a pigment_map.

I am curious about
#declare GreyTest = 0.001 + abs(TestK(X,Y,0) -
abs((TestR(X,Y,0) + TestG(X,Y,0) - TestB(X,Y,0))));

What is the underlying logic/reasoning behind this "greyness test"?

> > there are edge-finding algorithms that give you the gradient of the image as a
> > bonus.
>
> Hmm - I need to think about these things. Interesting suggestions.

https://www.youtube.com/watch?v=uihBwtPIBxM
skip to 3:30 if you want.

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