R MR

Thanks for the suggestion. Just to update — I tested the same scene with the same Houdini version and the same settings on another computer, and the flickering and aliasing issues were completely gone. So I'm guessing it might be related to some files or settings on this particular machine. Either way, I can now switch to a different computer for work. Really appreciate all your help over the past few days!

I just tested it — I rendered the same scene without the sand particles, so only the watch is visible. The flickering is still there, though. It's subtle, but you can definitely see it on the watch surface.

So it seems the flickering isn't caused by the sand particles or the high particle count. It's something else in the scene — maybe related to the material, the lighting, or Karma itself.

I've attached the render without sand.

thanks again!

Thanks for your suggestions — I really appreciate it.

I've done more testing based on the suggestions:

I turned off the denoiser — flickering still there.

I increased the samples significantly — I'm using Karma XPU and pushed Path Traced Samples up to 1024 — still flickering.

I even tried setting the roughness on the sand material all the way to 1 — and the flickering is still visible.

At this point, I decided to do a quick test by exporting the same scene to Blender and rendering it there — and guess what? No flickering at all.

So I'm starting to think this is likely an issue with Karma itself, rather than my scene setup or sampling settings.

I've attached a short clip rendered from Karma so you can see what I'm seeing.

Has anyone else run into this kind of reflection/refraction flickering in Karma, even with high samples and denoiser off? Any insight would be greatly appreciated!