Cycles: reducing fireflies?

Hi @nathanletwory,

is there already a way in Rhino (6.9) to reduce the fireflies? Here a test:

Cheers and thank you


P.S.: And is there a cycles category in discourse?


There is no separate category since it is an actual part of Rhino, so main Rendering category is fine.

@Holo showed a way to have a button with which you can quickly set direct and indirect sample clamping with which to greatly reduce fireflies:

Perhaps some of these techniques, shown in Blender might work:

They indeed work mostly.

  1. This means using rectangular lights, as they can be scaled in size
  2. Shadow sizes aren’t easily changed, expect somewhat for spotlights
  3. Skylight (and all other lights) are already set to Multiple Importance Sampling
  4. Filter can be set through advanced settings like clamping
  5. Also caustics can be set there. Especially for full-interior and exterior shots I find these can be safely turned off. Mostly useful for closeups of glasswork - yet caustics are on by default
  6. Clamping is what I responded with
  7. Yup, samples. For glass and reflective materials more is often necessary. Generally you work on lookdev with lower sample count 50-200 is often enough. The save and start a session with say 1000-10000, higher when reflective/glass materials are used.

Edit: I’d love to add support for the denoise filter, but that isn’t yet at the top of the list.

Thank you all for your help,

I’ve only used the skylight at the moment.

This cycles tipp helped to kill all flies:



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Sorry @nathanletworym,

another question. What brings caustics up? I have set the cycles option NoCaustics=NoNoCaustics, but it seams there is still something missing?




Unfortunately Cycles caustics is nowhere near anything one might understand under caustics. There has been some effort in adding proper sampling that supports advanced caustics, but that isn’t nearly done.

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Use a somwhat darker gray for the glass, it’ll leave a clearer shadow. Looks like you have (almost) full white used.

edit: in the quick render below the top glass has full-white, which means no light filtering at all, meaning no shadow at all. The bottom glass has color set to a very light gray (245,245,245). The scene is lit with just a sun.

render @ 16k samples

older render ~150samples

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Sigh. Seeing that, reminds me, I wish Cycles could do chromatic aberration/dispersion.