Am 29.12.2013 02:49, schrieb Cousin Ricky:

> What surprised me is that POV-Ray's native dispersion changes the hue of
> each spectral color.  For example, the violet extreme is ultraviolet
> blue for the high temperature white, and reddish purple for the low
> temperature white.  (It's still a whole lot better than POV-Ray 3.6
> dispersion.)  The spectral render merely adjusts the intensity of each
> band without changing its hue, as expected.

This effect is due to official POV-Ray doing all colour math in RGB 
space. The problem is that the human eye's sensors for long wavelengths 
(red) are also sensitive to very short wavelengths (violet); thus, when 
translating a very short wavelength to an RGB colour you do get a deal 
of R in there (about 24% of the B channel at 400 nm, at least with the 
table POV-Ray is currently using).

Now in official POV-Ray, the resulting colour in dispersion is computed 
as the component-wise product of the refracted light's RGB colour and 
the RGB colour corresponding to the given wavelength.

When the light has a high colour temperature, there is only little R in 
the light's RGB colour; thus, at e.g. 400 nm, the resulting colour will 
be R = 24% * little, G = 0% * some, B = 100% * plenty, resulting in a 
very blue colour hue.

On the other hand, when the light has a low colour temperature, there is 
only little B in the light's RGB colour, but plenty of R and G: thus, 
again at the very same wavelength of 400 nm, the resulting colour will 
be R = 2%% * plenty, G = 0% * plenty, B = 100% * little, resulting in a 
very violet colour hue.

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