[Radiance-general] RGB to Radiance definition

[Germán Molina Larrain]

Dear All,

I am trying to integrate easier ways of defining materials in Groundhog,
for which I have the following doubt. How can I define a Radiance material
(i.e. plastic, metal, glass, etc.) from an RGB combination and the global
Reflectance (transmittance)? The purpose of this is to enable "eyedropping"
a color, and assigning a reflectance or transmittance to it.

What I initially did was to find the combination of RGB reflectances that
satisfied the rho = R*0.265 + 0.67*G + 0.065*B while maintaining the
original proportions of RGB. However, since the RGB color that comes from
the eyedropper has Black/White components (which intend to emulate shadows
and different light exposures), my procedure often ends up returning an R,
G or B channel that is greater than 1.

I guess my question is: Is there any way of reconstructing the R, G and B
reflectances (or transmittances or whatever) from an RGB pixel? Maybe
playing with HSL space or something?

Best,

Germán
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