Path tracing rendering - transparent material looks pixelated


most of the time when I render using path tracing, transparent materials look strangely noisy, have a look at the train’s windscreen in this video as an example.

I don’t have this issue with the realtime renderer.

I have the feeling that I am lacking some knowledge about the specifics of this renderer. Can anybody help?


Hi Bruno,
This is a video from the movie capture or filmed while simulating in “real-time” with the UI?

For RTX Referenced Path Tracing and RTX Accurate (Iray), the higher the samples per pixel rendered on each frame, the higher quality you get, though of course, the more time it takes to render it out a full movie.
If this is done with the Movie Capture you might be using the default value of 1, which is not enough to resolve and clear out the noise here. So I suggest you first try to change this value to see if it improves.

Finding a good spp number is highly dependent on your scene (geometry, materials, lights), resolution and render settings.

If you are interacting with the viewport in the UI one think you can check are the stats in the viewport.

It has an indication on how many samples per pixel have been rendered (here, already the full 64 of my default 64 spp). You can adjust the spp under Render Settings → Path-Tracing → Total Samples per Pixel.

If you are using the Movie Capture, you can change this setting in the “Rendering” section

As an example, check this video, Workflow Basics Part 3: Scene Editing and Rendering in Omniverse - YouTube min 4:36 you can see while the camera moves it is using 1spp, once it stops it starts resolving and clearing out the noise, and the stat of the spp (top right of viewport) is increasing for some time. At 5:33 the render settings for the movie capture inc. the spp are also discussed.

For a more in depth overview of RTX Renderer you can also check this talk, has a lot of good info The Omniverse RTX Renderer | NVIDIA On-Demand

It’s rendered using movie capture. Let me try your suggestions and give you feedback…

Just tried to movie capture with 1spp and 8spp, and it makes a huge difference in quality - unfortunately also performance wise. But that’s a different topic.


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Here is some rendering tips that can help you too. Just follow from the beginning.

At the post June 28 you can stop, from there on its just about eye reflection…

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