I'm working on an animation where a cube of jelly falls from the sky (it's best not to think too hard about it).


Here's frame 45: speckled jelly

There are loads of speckles, which I've learned are called "fireflies" from this post. I tried the despeckling suggestions at its referenced link, but each of them has a pretty serious problem.

For instance, if I turn off caustics, the fireflies disappear, but the bottom plane of the jelly where it contacts the floor turns black. It only makes sense, I guess; blue filtered through red would be black, and if there are no caustics, light can't bounce to the floor.

without caustics

If I keep the caustics and denoise the RenderLayer with the default settings, the jelly gets all splotchy and dirty-looking. denoised

I've also tried making my lamps bigger, which does make the bottom more visible, but the fireflies are just less bright, and the shadows fade too:

faded everything

Ugh. Other things I've tried:

  • Increased the render Sampling samples to 1024; no help. I accidentally set the preview samples to 0, and came back in 3 hours or so; it had reached 30K samples and the fireflies were gone, but c'mon, 3 hours?
  • Increased the render Light Paths transparency and bounces. I've tried lots of combinations, I can't even remember them all. Mostly increasing max, diffuse, and transmission (the cube has no glossy or volume shaders).

Could someone explain where these fireflies are coming from, and how to get rid of them without losing my shadows, my bottom transparency, or my render time?

  • $\begingroup$ Try using clamp indirect. Start with a number like 10 and go down a bit depending on the brightness of your lights (never clamp under 1.0). Read: blender.stackexchange.com/questions/96101/… and blender.stackexchange.com/questions/134626/… other thing to try is having larger light sources. $\endgroup$
    – user1853
    May 11, 2019 at 16:57
  • $\begingroup$ Setting the render's Clamp Indirect to 10 makes the fireflies fade, but doesn't get rid of them. I decided to use Newton's method and went straight for 1, and that fades the fireflies even more, but they're definitely still there, especially in a close up view. $\endgroup$
    – Judebert
    May 11, 2019 at 17:03
  • $\begingroup$ The value for clamping depends on the brightness of your sources (which we have no way to know). $\endgroup$
    – user1853
    May 11, 2019 at 17:21
  • $\begingroup$ I'm still trying to upload the blend file. No idea why Blend-Exchange keeps failing on it. The lights use a strength of 200 to get the illumination and shadows. I got a fairly good result with Clamp Indirect 1.0 and 1024 Render Samples, but it takes almost 10 minutes per frame. $\endgroup$
    – Judebert
    May 11, 2019 at 17:25
  • $\begingroup$ Thanks, still working on it. blend-exchange.giantcowfilms.com keeps giving me an upload error. I suppose I could try screenshots of the various settings... $\endgroup$
    – Judebert
    May 11, 2019 at 17:33


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