I would be very interested in seeing an error comparison of this technique against something like a full-wave PDE or integral equation solver. Demonstrating that the (fast) raytracing solution converges on the (slow) full-wave solution as e.g. the number of rays goes up is a very powerful statement.
Spectral Ray Tracing
41–45 of 45 posts
Re: Spectral Ray Tracing
#42Re: Spectral Ray Tracing
#43Earlier quoted context omitted.
Funny, I added the original implementation of spectral rendering to Lux and then they took it out :D
Why did they remove it?
I have no idea (it wasn't exactly the same project, LuxCore vs Lux), and PBRT, on which Lux was based, later moved to full spectral rendering.
I guess they feel they'd rather reduce register pressure a bit than support it.
Re: Spectral Ray Tracing
#44Earlier quoted context omitted.
It's possible to implement this efficiently using light tracing - the final value in the image is the (possibly transformed) contribution from each light source, and since you have the spectrum of the light source you can have the spectrum of the pixel. Until you encounter significant dispersion or thin film effects, that is, then you need to sample wavelengths for each path, so it becomes (even more of) an approxima…
This won't work, because intermediary objects filter the spectrum of source light. Also in some scenes you can have so many lights contribute to a single pixel, that it's cheaper to save entire spectrum on each pixel. Consider how sky is a huge light that you can't save as a single light source, because different areas of that sky contribute differently - effectively one sky-light is an equivalent of millions of poin…
This actually does work and is implemented in a few renderers.
You can obviate the issue of having too many lights by combining them into light groups. As for area lights with different spectrum at different locations, you simply can't change the distribution after the fact.
In the tracing pass, you can store the shading interactions, then apply them across the spectrum of your light at the end after the shading pass, onto brightness values that you save for each light (group).
Changing the spectrum of the light after the fact, however, is going to be an approximation, but not changin the brightness.
Re: Spectral Ray Tracing
#45Earlier quoted context omitted.
This won't work, because intermediary objects filter the spectrum of source light. Also in some scenes you can have so many lights contribute to a single pixel, that it's cheaper to save entire spectrum on each pixel. Consider how sky is a huge light that you can't save as a single light source, because different areas of that sky contribute differently - effectively one sky-light is an equivalent of millions of poin…
This actually does work and is implemented in a few renderers. You can obviate the issue of having too many lights by combining them into light groups. As for area lights with different spectrum at different locations, you simply can't change the distribution after the fact. In the tracing pass, you can store the shading interactions, then apply them across the spectrum of your light at the end after the shading pass…
Thanks! Good to know.