Progressive sampling for only indirect rays?

Say I render an image and realize that the indirect lighting, caustics and some shadows are too noisy and need more samples. If I exported that image as an .exr file (just the combined pass), is it possible to then render only the indirect rays and overlay the result over the original render in the compositor in order to average out only these areas, or would I have to render another combined pass? And would it even be faster than rendering the entire image?

Secondary rays need primary rays to even exist. So no, I guess there’s nothing to be gained.

I’ve never tried with this specific case of “Indirect rays”, and I think that “only” indirect rays are not renderable as Steffen said.

Nevertheless, generally speaking when you don’t have enough samples, you can save the image, relaunch a render, and add both of them together with the compositor. In that case, these two things are important :

  • Setting a new seed for the new render (otherwise you would be converging to the same result and the merge would be no use)
  • Merging with a ratio which respects the sample ratio. For example if first image is 512 sample, and second one 1024 samples, you would merge them with .333 ratio

See you ++ :slight_smile:
Tricotou

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