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Very noisy ray tracing example, wrong GPU?

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    #16
    Originally posted by Arkiras View Post
    Raytracing is noisy, period. This is an inescapable fact of how it works. It has to take many samples for each pixel in order to determine the final output...

    In realtime rendering the sample budget is typically 1 (one) sample per pixel. You ever tried to do an offline render with a single sample? It's noisy. So the result is typically run through a denoiser, but denoisers are not magical, they can only do so much. There are also many different ways you can denoise to varrying degrees of success. I don't know what denoising method Epic is using, neural network denoisers are popular in offline rendering but afaik are usually too slow for realtime.

    This is compounded for diffuse reflections, because diffuse reflections require significantly more samples to converge on a noise free result. This is why in that video, he only uses raytraced reflections for the glossiest (least rough) surfaces such as the car body and glass, while the wheels use reflection captures (reflection captures are not raytraced reflections)

    The original poster has a number of problems:
    1. The obvious, he's trying to get diffuse reflections out of a single sample
    2. His geometry is not well suited to realtime rendering, he has extremely tight chamfers which are resulting in a lot of aliasing
    3. It looks like he's disabled temporal antialiasing which would have smoothed out the result slightly and improved the aliasing
    4. It appears he is rendering at below 100% screen percentage which is just exagerating the aliasing
    Because the noise stems from lack of samples, if you don't care about realtime performance then you can easily eliminate them simply by driving the sample count through the roof. Set your reflection samples to 30 and the noise will be much less noticeable. (Note that this will not work for final gather GI because as far as I know, that is locked at 1 sample)

    If you want to eliminate the noise without raising the sample count then you need to use non-raytraced reflections for diffuse surfaces (such as reflection captures). That's all there is to it. There is no other solution that I am aware of.
    Thank for the feedback. The scene is Unreal's own "automotive visualisation" demo scene. I thought that would default to a good result, but alas, it doesn't. I will work with your feedback!

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