"Kenneth" <kdw### [at] earthlinknet> wrote:
> > The other one of interest is .gray which I guess averages out the rgb values
> > (I've never used it).
>
> The .gray 'averaging' scheme seems to be full of black magic and voodoo. I've
> lately been trying to figure out just *how* it produces its values (armed with
> the only formula found in the docs, at "HF_Gray_16"...which offers no real hint
> of the underlying computations.) But I'll leave that question for a later post
> of its own. All in all, very mysterious!

The isosurface tutorial page mentions it:

gray value = Red*29.7% + Green*58.9% + Blue*11.4%

and gives a more thorough run-down on colour dot operators. Look here:

http://www.povray.org/documentation/view/3.6.1/73/

and scroll down to 1.3.3.3.7 - "Pigment and noise functions".

Bill

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