The downside is that this is slow. An RGB-ray traces the whole spectrum for one ray (approximated by an RGB triplet). The single frequency ray does not. If you try to send a binned spectrum in the ray, what will happen is that as soon as you hit something refractive, they will go in different directions, so you no longer have a full spectrum. All the complexity in a spectral renderer over an RGB one lies in handling performance: How to avoid the performance problems when you lose coherence. Apart from that it’s actually often simpler than an RGB renderer despite being able handle all those fancy spectral effects.
For a nice “reference” or “tutorial” one that isn’t plagued by the performance hacks needed to make it viable for large scenes, look at this one: https://github.com/TomCrypto/Lambda
IIRC the issue is that if you can ignore fluorescence, then reflection is simply an element-wise multiplication of the incoming light at the wavelengths under consideration[1] with the reflection coefficient of the material at those wavelengths. With fluorescence, that turns into a matrix multiplication, with obvious speed implications.
If only a single wavelength is considered at a time, then the wavelength must change upon reflection, otherwise there's no way for the fluorescence to occur. That can also have performance issues, for example conversion coefficients to/from regular color spaces needs to be recalculated.
At least that's my understanding having worked on a physically-based renderer which did do spectral rendering but not fluorescence.
[1]: using for example binned wavelengths or stratified wavelength clustering.
(I'm reminded of some company that developed a pair of glasses for color-blind people which enabled them to see "color". I think it was a similar princple.)
- colors that were previously the same could be now perceived different (a red car, a red flower, red light from LCD screen etc...)
- White / grey would still exist but be less common, as a lot of white / grey light would now be close to a new receptor
- Probably more distinguishable shades in the rainbow
Granted, our trichromatic vision is likely adapted to the scenery of this earth. We are most senstive to hues of green for instance. That being said, all things equal, wouldn't new grays appears with the new cone sensitivies just as the old grays would now yield a color response?
>- Probably more distinguishable shades in the rainbow
What I'm curious about is those pure hues we perceive that are infact the result of composites of wavelengths. Those equalities would break up. Two things that were once, say, equally orange could suddenly have different hues in the new mapping.
I'm even wondering if we all "see" / "perceive" the same colors / have the same response to the same hue (i.e. is my blue the same as yours ?!)
wouldn't new grays appears
Well, the prism/rainbow is the pure wavelength specturm, so that's one of the things that probably would turn out the same in the new mapping.
>I'm even wondering if we all "see" / "perceive" the same colors / have the same response to the same hue (i.e. is my blue the same as yours ?!)
The sensitivity range does vary between individuals. Some women are in effect tetrachromats because they have two sets of, I think it is, Red cones that are sufficiently wide apart. I find this very fascinating.