Ive <"ive### [at] lilysoftorg"> wrote:
> Wrong. Out of gamut values are indicated by one or more RGB components
> with *negative* values. It has nothing to do with HDR. And IIRC POV-Ray
> does clip negative values - but it is a long time since I looked at the
> source - so you might know better.

Well, if RGB components can be negative, then obviously we're not talking about
a straightforward 3-band spectrum (or am I missing something here?) as
simulated by POV-Ray.

So there's two things involved here:

(1) A rendering engine, simulating three spectral bands (which, for physical
reasons, cannot have negative intensity), and

(2) the human visual system, partially mixing these spectral bands for a certain
color perception (due to the receptor pigments' spectral response ranges
overlapping).

So I think there cannot be an unsurmountable problem with the render engine -
only with how to present the results to the human eye.

There *is* of course the problem that the render engine's spectral bands are by
convention assumed to be identical to the emission spectrum of the user's
display's phosphors. However, this is not a necessity.

So the right thing to do would be to (A) choose properly defined spectral bands,
(B) make sure color values are coded accordingly, and (C) apply some
transformation to the output to transform the quite arbitrary 3-band image into
a target color space of choice.

If this still yields inferior results, there would still be the possibility to
model a larger number of spectral bands, using macros to define the colors, and
and render the scene in multiple passes, picking three of those bands per pass.
Again, the results would have to be transformed into the desired color space.

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