Hey Gang - So I was playing around with the Lumen GI vs the (apparently) deprecated RT GI. There is a slider for Final Gather quality that defaults to 1 and slides up to 2. You can type in any variable. Adjusting this from 1-2 seems to have no visible effect. Typing in something crazy like 100 also has no effect. Are there more Lumen GI settings available under the hood?
Can anyone at Epic provide on info on how this setting correlates (or doesn’t) with the previous RT GI settings like Samples per Pixel, Max Bounces etc? Also, if it is a consequential quality setting, how we can call it from command line for movie render queue renders? I.e. When working you would keep your RT GI samples to 1, but crank them to 48 for MRQ renders etc.
Thanks!
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Hi, I was looking for those settings. Where did you find them?
They’re in the post-process volume, but settings have changed a lot since EA: the final gather (essentially) decreases noise in GI, but at a performance cost. From my tests, it ranges from .25-8 in terms of settings, and it can make a big difference in scene quality. There’s the lumen scene lighting quality, which is effectively GI in reflections, and then a few other settings that control lumen scene size and update scene.
And, as someone who went through every single lumen CVar in EA, I can say, there are many more settings hidden under the hood. This is a very good thing: Nvidia’s RTXGI exposes all of them in the Post-process volume, and it makes it a mess to navigate. Lumen settings change things ranging from probe density and behavior, tracing method and quality, history weighting, experimental features, and more. You can achieve very high-quality images with lumen ,but it might take a ding to real-time performance.
And as someone who’s worked with RTGI in the past as well, I’ll also say lumen is an entirely different, way more complex beast. It’s not just tracing rays, it’s accumulating, processing, and filtering multiple different light transport methods and throttling all operations to maintain performance . While there’s probably a list of best-quality CVars somewhere, the general behavior is this: Lumen GI has infinite bounces, lumen reflections support a single bounce, and the higher quality settings only really reduce noise.
One caveat: in the newest versions of UE5 on github, lumen supports high-quality translucent reflections in a separate check in the post-process volume. That will yield better results than the default radiance cache, and needs to be specifically enabled.