[Tooster]

I was sure it must have been invented already! I've been trying to look for this idea without knowing it's called "spectral rendering", looking for "absorptive rendering" or similar instead, which led me to dead ends. The technique is very interesting and I would love to see it together with semi-transparent materials — I have been suspecting for some time that a method like that could allow cheap OIT out of the box?

[dahart]

I’m not sure carrying wavelength or spectral info changes anything with respect to order of transparency.

It seems like OIT is kind of a misnomer when people are talking about deferred compositing. Storing data and sorting later isn’t exactly order independent, you still have to compute the color contributions in depth order, since transparency is fundamentally non-commutative, right?

The main benefit of spectral transparency is what happens with multiple different transparent colors… you can get out a different color than you get when using RGB or any 3 fixed primaries while computing the transmission color.

[csmoak]

The main benefit I see is being able to more accurately represent different light sources. This applies to transmission but also reflectance.

sRGB and P3, what most displays show, by definition use the D65 illuminant, which approximates "midday sunlight in northern europe." So, when you render something indoors, either you are changing the RGB of the materials or the emissive RGB of the light source, or tonemapping the result, all of which can approximate other light sources to some extent. Spectral rendering allows you to better approximate these other light sources.

[zokier]

Conventional RGB path tracing already handles basic transparency, you don't need spectral rendering for that.

[pixelesque]

Not exactly what parent poster was saying (I think?), but absorption and scattering coefficients for volume handling together with the Mean Free Path is very wavelength-specific, so using spectral rendering for that (and hair as well, although that's normally handled via special BSDFs) generally models volume scattering more accurately (if you model the properties correctly).

Very helpful for things like skin, and light diffusion through skin with brute-force (i.e. Woodcock tracking) volume light transport.