Am 15.04.2013 14:57, schrieb Bernard:
> May I, as a beginner in PovRay but a long-time worker in colour technology, post
> a word of caution?
> Most people do not understand colour. A straightforward 3D system like rgb is
> quite complicated enough for them.

This is one of multiple reasons why I'm trying to figure out a good way 
to convert from RGB to some synthesized spectrum: It'll allow to use 
spectral math inside the render engine, but still use the RGB colour 
model in scenes.

But you're making an interesting point there: Maybe we should also 
provide for more intuitive color models to be used in scenes.

I think it is obvious that one of the three parameters for such a color 
model would need to govern (1) the hue, while the other two should not 
influence it in any way.

For easy use with light sources, it should be possible to adjust the 
brightness in the most simple manner possible, i.e. by tweaking just one 
single parameter. Therefore, for any given hue the second parameter 
should govern (2) the saturation, and for any given combination of hue 
and saturation the third parameter should govern (3) the brightness.

There are two other properties that would both be desirable but can't be 
fulfilled together: It would be nice for the third parameter to directly 
specify luminance (i.e. what the .grey component returns). On the other 
hand this would make it extremely difficult to specify a pigment with 
maximum chroma for any given hue, which I'd personally consider a no-go.

The above constraints rule out both chroma- and lightness-based models, 
even though they would have merits of their own. I guess in the end the 
model will inevitably have to be a variation of HSV (aka HSB).

A major open question would be whether to specify the brightness in 
terms of a perceptual or physical scale.

As for saturation, with RGB-based color math it should probably 
represent saturation with respect to the gamut of the internal color 
space, while with spectral-based color math I guess it would make sense 
to have it directly represent excitation purity.

Thinking about it, this type of parameterization might also make it 
easier to convert from user-specified colour to a synthetic spectrum.

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