Hey all,

I've been playing with the new Indirect Lights as a means to generate photon maps for caustics in pbr renders. I've been having a hard time dialing the parameters in so that I can remove the noise but retain the meaningful detail. Using a large value in the “Prefilter Samples” parameter helps with the noise but softens the solution in a way that isn't concise to the finer detail of the geometry. I've been playing with the “Filter Samples” parameter as well but I need to set to values up to and above 1000 before I get a result that begins to resemble what it is that I'm looking for - a clear result free of any unmotivated phenomena. I believe that I'm generating more than enough photons for both the caustics and the indirect lighting, using values up to and over 1,000,000.

Has anyone else had any experience with this sort of thing? I've looked around, but details are sparse and examples even more so as this is a fairly new workflow.

Andrew?

stu

Hey - yeah, the behavior you are seeing would make sense. The caustic photon distribution is pretty random, so to eliminate all the noise I'd expect to need to filter up to 1000 photons to get a smooth result. For large image resolutions, it may be better to perform this in the prefiltering step since then it will not be necessary to filter that many photons for each shading point.

On the other hand if a little noise is tolerable, you should probably see pretty consistent patterns of photons between frames in the latest 11.0 builds, so if a little flicker-free grain is acceptable you could use lower filter counts.

Andrew

Thanks Andrew.

I'm a little mixed up with regards to “Prefilter Samples” vs “Filter Sampling” and how they relate to each other, and what exactly it is that they're doing mathematically. Say I generate 100,000 photons - what's happening behind the scenes if I set “Prefilter Samples” to 1,000? And if I set “Filter Sampling” to 1,000? Are they effectively reducing the number of photons used in the final illuminance calculation to 1,000? If I set them both to 1,000 is it counter productive?

i'd also love to get some info in this department.

i've really been struggling to get sharp, blotchy free caustics in H11.
i used H10 to generate caustics for most of the shots in the Free Willy movie we did a while back, i can't remember having such difficulty getting sharp caustics.

fine grain isn't really a problem, but there seems to be a larger blotchy feel to caustics, not sure if it has something to do with ray samples when generating the photons?
i can get rid of them by bumping up the filter samples, but then they are just soft..
you can kinda see blotchy caustics here:
http://www.vimeo.com/19779854 [vimeo.com] ok maybe the resolution is a bit small, i'll try render a full hd frame later.

jason

stu
Thanks Andrew.

I'm a little mixed up with regards to “Prefilter Samples” vs “Filter Sampling” and how they relate to each other, and what exactly it is that they're doing mathematically. Say I generate 100,000 photons - what's happening behind the scenes if I set “Prefilter Samples” to 1,000? And if I set “Filter Sampling” to 1,000? Are they effectively reducing the number of photons used in the final illuminance calculation to 1,000? If I set them both to 1,000 is it counter productive?

Thoughts Andrew? Any clarification that you could add would be very helpful. As pbr becomes increasingly viable I'm looking for every bit of efficiency that I can squeeze out of the tools.