I have a scene in which I want to reduce noise/fireflies by the method illustrated here, i.e. rendering twice (or in my case 4 times, but the theory is the same) with lower sample count but different seed and combining the results with blending mode "Darken".

My scene is an animation with ~500 frames so rendering it twice would result in a lot higher used storage. What I'd like to do is tell blender

  1. render frame 1 with render seed 1
  2. render frame 1 with render seed 2
  3. combine those two frames to one using darken
  4. combine my compositing nodes to the result of step 3
  5. output that as one file
  6. repeat for every other frame

it doesn't matter for me if steps 1 and 2 are done at the same time (if that's even possible) or not as I assume the total duration would be the same. Preferably this should work without python scripts since I plan on using a render farm which doesn't support those.

How can I do this?

Blender version used is 3.3.1 but if there's a solution that requires 3.4 updating would be no problem.

  • $\begingroup$ btw I'm not very happy with the title of this question but can't think of something better - suggestions/edits are welcome :) $\endgroup$
    – jng224
    Dec 12, 2022 at 22:39
  • $\begingroup$ are you looking for automating this without python? blender.stackexchange.com/questions/5017/… $\endgroup$
    – R M K
    Dec 12, 2022 at 22:52

1 Answer 1


The comment by R M K pointed me in the right direction (thanks!) and I've been able to figure out a solution myself.

What I ended up doing was creating multiple scenes (within the same file) for which I copied all objects and render settings from the original scene and then only gave them a different seed.

In the compositor I then used a node setup like this enter image description here

with some other nodes that are not relevant to the denoising behind. I suppose I could also have enabled the other passes (Emit, AO, Depth) in every scene and apply the same process to them but considering that they didn't have any noise/firefly problems I just left them as they are.

During rendering, every scene gets rendered separately1 and then composited at the end. Since you can easily get away with 1/4 of the original sample count, the overall time needed is pretty much the same.

1 for some reason (maybe just a bug) every scene other than the original doesn't show any progress during rendering (it's just a transparent image) but it still works and after it's finished you can preview those scenes in compositor.


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