System Information
i7 3930k
40GB RAM
Nvidia GeForce GTX660 (driver version 21.21.13.7653)
windows 10 pro, 64-bit
Blender Version
2.78a e8299c8
Short description of error
cycles renders artifacts, that look like NaN errors: see image
Exact steps for others to reproduce the error
open scene
Doesn't look like a bug, just reflections from the lamp. Disable MIS for the lamp and the birght spots go away.
@Sergey Sharybin (sergey) Can you confirm?
The noise is coming from caustics i think. Usually using Filter Glossy will help, but it has no effect on Sharp distribution. Doing something like D2416 will help here.
At least that's what i see from quick investigation and might be wrong.
In any case, unsolvable noise is not a good thing anyway and disabling MIS is not really a solution in real production scenes.
Maybe @Brecht Van Lommel (brecht) can throw some ideas here as well :)
I think D2416 would be good for this case.
The other workaround is to use the transparent shadows trick, which might be good to add as a builtin feature of the glass BSDF node:
https://docs.blender.org/manual/en/dev/render/cycles/optimizations/reducing_noise.html#glass-and-transparent-shadows
I've fixed some issues in D2416 and committed it now. So now there is a way to make his file to be less noisy.
Surely having some built-in feature for transparent shadow for BSDF will be interesting, but think that's out of the scope of this report.