Light actors give the highest quality detail for the lumen scene, first bounce looks pretty good, but it quickly gets worse from them.
To my knowledge the artifacts are pretty much the results of indirect lighting. While turning them off results in a clean scene, you’ll need those indirect/secondary lights for the scene’s lighting to look natural.
Anything surface directly visible to the camera will be rendered with no issue, surfaces that’s visible only in reflection will have those artifacts since they’re not part of the surfaces that Unreal’s screen tracing is calculating, resulting in low quality lighting renders.
I assume those artifacts in this case are actual spots where the light rays bounced off producing the low quality light cache that’s either not cleaned up or simply left really rough on purpose so less processing power is used to make real-time raytracing possible. I haven’t dug into UE’s rendering code yet and not sure if I really want to, so I’m not sure how they’re handling that in the back, above are an educated guess based on what I observed so far.
I’ve been looking into this problem for a while. I think it’s innate to path tracing of Lumen. For a consistent surface, PT just choose some rays to trace and blend them together. Since Lumen is also sort of screen space rendering, the sample amount is good when it’s in screen, and bad when it’s out of screen. The problem goes extreme where there are shadow and indirect light. So the reflection of out of screen part is provided by Lumen hardware ray tracing, I guess if you increase this sample resolution, it will look better, although it’s a performance trade off. For me, I just drag in a PP volume, and set each variable related to Lumen to a really high number, let’s check out before and after.
before
after
What matters the most is the fisrt value “Lumen Scene Lighting Quality”, which controls the overall sample resolution of Lumen.
The core issue that’s essentially intractable is the surface cache: Indirect lighting is cached to meshes, and because it’s stored as texels in an atlas, it has a finite resolution. Lumen dynamically raises and lowers the resolution of assets in the surface cache according to a variety of factors including distance to the player, but it can only do that so much. Furthermore, because every object in the lumen scene is competing for space, it will eat up VRAM quickly if you give it the chance. All and all it essentially means you can never get GI in reflections that will match the primary view, you can merely get (hopefully) close enough that it won’t be too noticeable.
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Having the same problem. It’s for sure is because of indirect light as all this artifacts are gone when I set “indirect lightning intensity” to 0 for my light sources. Though it makes light totally unrealistic…
I can get nice reflections in the mirror when I use “Standalone Ray Traced (Deprecated)” in reflections settings in PPVolume. But it also causes strange blue reflections on all objects in the scene. And my white walls with warm light sources appear blue in the mirror. It looks horrible.
Also I’ve seen some tutorials for Lumen reflections and people did have quite nice mirror reflections with the very same settings like mine.
I do have “Use Hardware Ray tracing when available” as well as “Support Hardware Ray Tracing” on but I don’t see any difference in my reflections.
So I don’t understand why Standalone Ray Traced is marked like deprecated as In my situation is sounds like “nice clean reflections are deprecated”, lol.
Hovewer I can use tham as local PPVolumes next to the places where I heve mirrors and mirrowlike materials, if anyone could help me how to deal wit this blue tint everywhere.
P.S.: I’ve found that tis blue tint is caused by rayleigh Scattering in SkyAtmosphere component on the scene. Changing it changes both sky and ray traced tint colors.
Not sure how to get rid of it… It is seen even in the room with no windows and door closed.
P.P.S: With Standalone Ray Traced the reflection il lit with blue light even if I’m in a closed room with no light sources in it. Seems like sky doesn’t cast shadows with RayTracing. With lumen it’s ok. Raytraced shadows is on in project settings.
Stand alone reflections are the early ray traced reflections that were initially added to UE4 before Lumen and UE5. They are basically their own pass, not as physically correct, don’t work with all the lighting features, expensive, and not integrated with lumen.
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Standalone RT reflections don’t actually do any specular occlusion, so the skylight is leaking through everything; it’s just the nature of the system.
The key thing is to make sure you have hit lighting for reflections enabled in the PPV, and a bounce count of 2 or greater. It won’t be perfect (it can’t be), but it will be better and probably acceptable quality-wise.
But how can i rurn on proper ray tracing within my Post-Process volumes?
Actually i think That i’m going to swithc from lumen to baked lighting as lumen do cause artifacts not only in the reflections (though they are not nearly as strong) but I want to try raytracing for mirrors or some other high reflective objects but not for the whole level.
I’m late in replying, assuming rendering time isn’t a huge issue, path-tracing could work for you? I didn’t use it in my project because it just takes too long, can’t afford the wait.
Same, I am also working on developing ArchViz PC VR experiences, so I need to strike the balance between high quality and performance. Lumen reflections are better for that balance against fully ray-traced.
Keeping the indirect light amount low in spotlights and removing any emissive materials have given me the best results to avoid artifacts in the reflections.
It’s a shame we still cannot disable GI for emissives, globally.