Fireflies with Glossy Multiscatter GGX
Closed, ArchivedPublic

Description

System Information
Windows 10 and GTX980m

Blender Version
Broken: (example: 2.78 62a6ed9)

Fireflies with Glossy Multiscatter GGX


1 Open the blenderfile
2 Render the file

Recently I noticed fireflies in my renders and wasn't sure where they came from as I used fairly high sample count (2048spp up to 8192spp), MIS, Filter Glossy 0.2 and had caustics turned off. I found that it's comming from high roughness values and glossy multiscatter ggx option. The fireflies do not appear with 'standard' GGX.
I am not sure if this is expected behavoir and hope it's a valid bugreport. When looking for informations I only found that multiscatter GGX tends to be noisier but nothing about fireflies.

Details

Type
Bug
Sergey Sharybin (sergey) triaged this task as Confirmed priority.Dec 13 2016, 12:44 PM

The code here is barely readable. Assigning to Lukas.

Sorry for ignoring this report for so long...
These fireflies aren't really a bug, it's just a shortcoming of the stochastic evaluation used by the MultiGGX model.

It should be possible to get rid of them by implementing MIS-weighted bidirectional walks as described here which should be rather easy with the current code afaics, but that's a ToDo, not really a bug.

So, I'll close this for now, but I'll look into implementing the improved random walks.