Volume mist causing noise around emission lamps.

Hi,

I’m working on a Mars rover scene, and I’m facing a little bit of an issue… I have a huge volume cube in the scene to get that misty look, but it causes problems with these little emission shader lamps that I have on the rover. Everything else clears up relatively nicely in the render, but the mist in front of these lamps keeps being noisy even after 100 000 volume samples and 8 hours O_o I need to get that down a little, because this is going to be an animation…

I just thought I’d ask if any of you have some little tricks to make the volume clear up faster. I’ve attached a part of the latest render so you can see the problem.

Things I’ve already tried:

  • branched path tracing, volume samples up to 50 per 1 AA sample (helps a lot, but still keeps being noisy)
  • clamping (helps, but easy to lose the nice effect)
  • multiple importance sample on lamps
  • changing lamps to a little area lamps with more samples (doesn’t help)
  • reducing volume rendering max steps and increasing step size (reduces rendertime a bit, no help for the noise)
  • rendering in 2.7k and then downscaling the image (might have helped a little time-wise, need to experiment more though)

I guess it could also be that this simply is an impossible scene to render efficiently… :no:
Please help if you know something that I don’t!


If it’s for an animation you might want to consider a mist pass instead of volumetrics, and then use some compositing glare on the lights to fake a glow around them. Good luck.

Mist pass tutorial

It’s just an issue with rendering with lights inside of volumes. If you use area lamps instead of emission materials you should see a lot less noise, but aside from that, throwing more samples at it is the only real solution. If you’re only interested in a mist effect, I wouldn’t recommend volumes anyway, that’s just unnecessary wasted render time.

Ok, thanks for the replies! I already tried to use area lamps instead of emission lamps, but it didn’t seem to have any effect whatsoever, which surprised me. Also I’ve considered using the mist pass, but I’d really like to have those little glares in front of the lamps (I’m planning on even thicker volume) and I know if I try to fake them it doesn’t look as good…

However, I also started to experiment with rendering the volume in a different render layer and masking out the landscape and the rover in that layer. The idea here is that I could blur the volume pass independently to take out the remaining little noise in front of the lamps. But that introduces some new weird problems that need to be solved… If I use opaque film, the volume pass looks just fine, but when I make the film transparent (to make the composite look better with natural alpha channel), all the glares in front of the rover disappear? I don’t understand the logic behind that.



(I applied a black background to the last image so you can see the effect)