Lumen Global Illumination Noise pattern on foliage

[Halukumben]

Lumen GI creates weird dark blotches moving around on the foliage and other plant models when there is no direct light on the objects:

Increasing Lumen GI settings does nothing to change the issue. There is a work around I could find:

Setting r.Lumen.ScreenProbeGather.ScreenTraces.HZBTraversal = 0 removes these blotches but also removes all shadowing from every foliage actor and two sided foliage material in the scene.

Here’s before:

And after:

Is there any other way to get rid of these without lowering the overall quality?
I use UE mainly for offline renders so performance is not an issue.

I don’t see this issue in anyone else’s videos on youtube ect. so I’m not sure where do I go wrong.

Win 11, UE 5.3 using RTX4090. Tried with every ray tracing option enabled/disbled in Project Settings.

[John_CTS]

Wondering if you found a fix for this?
I’m having a similar issue but with Tree foliage using Lumen. Tried a bunch of suggested Cvars, but none worked.
In the Project settings, I found if I changed the Anti-Aliasing Method from the default of TSR to TAA, that helped about 50%.

[JPTInteractive]

Does your foliage has distance field shadows? Similar thing happens when it is open in UE4. Can be different in 5.

[MostHost_LA]

This is similar of not the exact same of what Lumen does to Shadows when the rendering is set to use TAA I believe.

Try swapping out TAA to other methods first.
If the effect lessnes then you can try to make sure your grass WPO wind is writing to the velocity buffer for the temporal stuff to lessen fhe blurs.

It didn’t do much for the shadows, but this being grass it could be a valid answer.

[Dreyniak]

I have the same problem, I’m going crazy to solve it…

I tried unchecking that box, it seems to be a problem with the distance fields lights.

Then I tried making foliage two swided, but the problem persists.

[Frenetic]

@MostHost_LA

If the effect lessnes then you can try to make sure your grass WPO wind is writing to the velocity buffer for the temporal stuff to lessen fhe blurs.

How does one do this? Velocity-buffer?

[MostHost_LA]

Its probably called something different now since the doc results don’t show any relevant tutorials on it.

The velocity texture is the one used by the rendering pipeline to remove blur from around moving objects when using TAA.

I remeber it being an easy toggle for translucent materials

For WPO/objects i believe it requires changing project settings and mesh setup.

Here, watch/learn this as it probably explains it better than I or the Docs did

Anti-Ghosting Temporal AA - Unreal Engine 4 Guide

[Dreyniak]

I’ve found a half-solution, if you put this command on the console, reduces the sample of lumen.
For my project was nice!
r.Lumen.ScreenProbeGather.DownsampleFactor=8

[ZacD]

To expand on those settings and that value, Allows global illumination to be downsampled independently from the internal render resolution.

r.Lumen.ScreenProbeGather.DownsampleFactor [8 = Cinematic, 16 = Epic, 32 = High, 64 = Medium, 128 = Low]

Lumen Performance Guide

[Halukumben]

Yeah setting the downsampling to 4 or even 2 fixes this almost completely. I’m mostly using this for offline renders so performance hit in not important for me, hopefully people looking for a real-time solution var find something in the link you shared.