Description:

I'm experiencing severe aliasing/jagged edges on objects when rendering with Karma in Houdini 22. The problem is especially noticeable when the object edges are angled or diagonal to the camera.

What I've already tried (none worked):

Sampling — Increased Primary Samples from 4 to 16, 32, and even 64. No improvement.

Pixel Filter — Tried different filters like gaussian, minmax zmin, etc., and adjusted Filter Scale. No change.

Dicing — Increased Dicing Quality Scale to 2, 4, 6, and higher. No effect.

Disabling automatic subdivision — Used Mesh Edit LOP to set Subdivision Scheme to None. Still aliased.

Switching render engines — Tried both Karma XPU and Karma CPU. The issue persists in both.

Ray Bias — Adjusted Ray Bias values. No improvement.

Model topology — Confirmed models have clean topology with no N-Gons, normals are correct.

Key observations:

The issue does not occur when I disconnect the Karma Render Settings node and use the default render settings. As soon as I connect it back, the aliasing returns, even with all parameters at default values.

This suggests the problem is related to the Karma Render Settings node itself or how it interacts with my system, rather than the scene data.

My question:

Has anyone else encountered this issue? Could this be related to specific GPU models, driver versions, or some system-level setting that I'm missing? Any help or debugging suggestions would be greatly appreciated.

System info:

OS:

CPU: AMD Ryzen 9 5950X

GPU: NVIDIA RTX 3080 Ti

Is that pixel 1:1? Did you render that into the gallery and made sure you looked at it 1:1.

Thanks for the reply!

I did some more testing — I rendered out a short animation through MPlay and checked it there. The good news is, I don't see any aliasing in MPlay. So I think the aliasing issue is likely a display thing on my end when viewing in other software.

However, I'm still running into flickering, and this one I can actually see in MPlay as well.

Here's the strange part: if I set the material roughness to 1, everything is stable — no flickering at all. But as soon as I lower the roughness, both reflections and refractions start to flicker. I've already tried increasing sampling values (Primary Samples, Reflection Samples, etc.), but it doesn't seem to make much difference — the flickering is still there.

I also noticed that the flickering gets noticeably worse when using an HDR environment map for lighting.

I'm not really sure what's causing this. Any suggestions would be really appreciated!

I can‘t tell for sure, but I guess your render is denoised and your samples might be too low. Render a couple of frames without denoise to check if any of those pesky ultrabright pixels jump around. More samples might be in order.

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!

Does this happen without the sandparticle on top?

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!

Just for testing set the refractionlimit to 0. I would bet the fluckering is gone (also render without denoise to see if there are any crazy fireflies.

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!

great that it works. Intersting solution