Flickering or light variations if rendering with Anti Aliasing in Movie Render Que

Development Rendering
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Hi
I have a problem that always if I render with the Movie Render Que using Anti-Aliasing, I have a flickering or light variations at least in certain parts of the scene in my final renders.
Some of the light variations seem to be actually existing in the scene but are extremely emphasized during the use of the Anti Aliasing option while rendering.
Other light variations or flickering do not exist in the scene at all and are completely caused during the rendering process while using Anti Aliasing.
Especially Grass seems to be vulnerable but it is definitely not limited to grass and I have it in every Project I start.
The only option I found so far, is disabling the Anti-Aliasing option in the Render Que completely.
Then it does not matter what else I am setting up, it works fine (just without Anti Aliasing).
On the other hand, if I switch it on, it also does not matter what else I setup, I do not get rid of the flickering issue.
So I guess the issue must really be located somewhere inside of the Anti Aliasing Settings.
I have attached my render settings.
These are the settings I endet up with. I started with pretty basic settings and while trying to read through all the forums, looking for help, I added more and more options but without success.
Besides of the current settings I also tried:

Color Output on
Deferred Rendering off
Game Override off
no Console Variables at all
Screen percentage limited to 100%
No Warmup Frames
TSR Anti Aliasing
TAA Anti Aliasing
MSAA Anti Aliasing

Some of these settings might have worked a tiny bit better than others but none of them got rid of the problem.

Using UE 5.1
Win 11
3090

In this clip, the first iteration is with AA enabled. You can see the flickering in the right lower corner in the grass.
The second Iteration is without AA.

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@Lt.Kirby Did you find a solution to this problem? I’m having a similar problem in 5.3 version.

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Unfortunately not. My solution so far was checking, if it is still existing in UE 5.3 but your question is basically destroying my hope. I have not checked it yet.

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What AA type are you using? If its TSR there is a cvar for flicker period rejection you can mess with. But this has a possibility to introduce ghosting.
**r.TSR.ShadingRejection.Flickering.Period

That being said is there a reason why you do not want to render without AA and just let the samples dictate jitter for AA? Honestly I would remove all the cvar overrides you have in there unless you have a visual reason to add them. People find these lists online and just blindly add them and sometimes they end of hurting more than helping.

Also you are not doing any good by mixing Spatial and Temporal Samples in the deferred path. Rule of thumb for deferred/lumen is to use one or the other. If you want motion blur just use Temporal. If you do not, use Spatial.

Not sure if you have seen this but it might help.

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Hey @comlys I’ve already read your guide couple of times, thanks!

I have tested “r.TSR.ShadingRejection.Flickering.Period 10”, result is effected positive when I stand still on viewport but when I move around same issue occurs. I also tested with video renders and results are almost identical.

This is with “r.TSR.ShadingRejection.Flickering.Period 3” (Default)


This is with “r.TSR.ShadingRejection.Flickering.Period 10”

The grass asset used here is “Grass_Clumps_rbptq” from Megascans: https://quixel.com/megascans/home?search=Grass_Clumps_rbptq&assetId=rbptq
I downloaded via Bridge with medium quality inside UE5.3.2.
I have a feeling, this is related to Megascans foliage meshes and/or their materials.

Also in my architectural interior visualisation cases having 32 spatial & 1 temporal AA is worse than 1 spatial & 32 temporal AA. So I stick with that even though it’s slower.

image
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temporal32 below

temporal32 (2)
temporal32 (2)1920Ă—1080 101 KB

spatial32 below (Glitches more apparent on the wardrobe and under bedside unit)

spatial32 (2)
spatial32 (2)1920Ă—1080 105 KB

spatial32_HighestPPV below (Suprisingly increasing all the Lumen GI and Reflection quality to max doesn’t improve anything comparing to default values. What might be the cause for this? Does “Game Overrides” in MRQ has impact on this?)

spatial32_HighestPPV (2)
spatial32_HighestPPV (2)1920Ă—1080 104 KB

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The only difference between those renders was one was Temporal Samples = 32 and one was Spatial Samples =32? Thats surprising.

There are a few cvars that you can try to clean out Lumen a little more.

r.Lumen.ScreenProbeGather.RadianceCache.GridResolution 128 or 256

r.Lumen.Reflections.DownsampleFactor 0

Also if you are raytracing your shadows make sure you are upping the samples on the shadow casting light as well.

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Surprising indeed. Using temporal fixes the “problem”, so i’ll stick with that for now. But foliage flickering on videos is still an ongoing issue and pretty annoying.

I found out this cvar kind of fixes it but worsens the quality a lot.

r.Lumen.ScreenProbeGather.ScreenTraces.HZBTraversal 0

Do you have any hints related to this?

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I have started another project this time in UE 5.3, hoping the issues might have been resolved, but unfortunately I have the same problems again.

Attached is a video where you can clearly see the flickering in the bushes in the foreground as well as in the trees in the background. The flickering is even toned down a little due to the compression of the video here, it was even more noticeable in the original rendering:

I have tried several renderings now with different settings. The flickering is already existing if the only thing I change is the activation of AA.
Nothing else got changed besides of that which makes me believe the AA is really causing my troubles.

From here on I have tried multiple different settings like CVARs, Game Mode override ( in Standard Settings as well as only with “Cinematic Quality Settings” and “Flush Grass Streaming” enabled ), Color Output with Disable Tone Curve, Color Output without Disable Tone Curve, rendering in PNGs, JPGs and EXRs, Aces but nothing worked.

I am using UE 5.3.2
I tried
Spatial Samples 16; 4; 1; 1; 1
Temporal Samples 8; 16; 16; 64; 7

Override AA on
Anti Aliasing Method None

I tried this with No Warmup at all, With “Use Camera Cut for Warmup”, with “Render Warmup Frames” as well in Standard Settings for “Render Warmup Count” and “Engine Warm up count” and also with 250 each and 500 each.
I also tried “Render Warmup Frames” and “Use Camera Cut for Warmup” simultaneously.

I switched “Override Anti Aliasing off” (with Spatial and Temporal Sample Count 1 and 7)

I switched “Override Anti Aliasing off” and additionally “AA Method” to TSR; I used TSR with “Override AA”; TSR without “Override AA”

I tried to render in HD, 4k, 8k (flickering was always present but every resolution besides of HD also altered the lighting of my scene, no idea what is causing these troubles)

I inserted new trees and bushes as Foliage (the ones used in my scene are mainly static meshes) and switched “Distance Field Lighting” and “Cast Dynamic Shadows” off but the flickering was also visible in these new trees.

I started to use CVARs and added more and more, hoping one of them might be solving my problem. Finally I ended up with this list:

Cvars
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I used Scalability: Cinematic
Lighting Quality: Production
Material Quality Level: Epic
Rendered in MRQ

I bought and finally used the “Lightforge” Plugin for scene and rendersettings optimization and Optimized the scene with the following settings:

lightforge
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I also tried “Nanite Mode” Instead of “Mesh Fallback Relative Error” and I also tried cranking every value under “Lumen Settings” to its’ maximum value possible.

If I delete all Foliage, I do not have the issue even if AA is enabled!:

In this rendering AA is enabled but no flickering is occuring.
But the rock on the left is blinking like a mirrorball.
No idea what is causing this or if it has something to do with the foliage flickering, but the flickering issue seems to be clearly limited to foliage.
No idea why it is happening though.

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Hey Shaun
Thanks for your help and your guide.
Please also check out my new posting to my new project in UE 5.3, if you like.

I used “AA Method None” and “Override AA” but I also tried TSR. There seem to be no differences according the flickering issue.

If I do not use AA, the scene gets rendered properly but without AA. This seems to be causing noise especially when it comes to moving foligae and water surfaces and generally the scene appears to be cleaner with AA especially around hard edges in combination with camera movement, if the flickering issue could get solved of course.

The CVARs have only been added because of the flickering, hoping, one of them would solve the problem. The flickering also persists without any CVARs.

I have tried several different Settings when it comes to the Spatial and Temporal Sample Count, also ones without mixing like 1/16 or 1/64 without improvement.

I also checked your guide but also could not get my problem solved but thanks again anyways.

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I tried your CVAR as well unfortunately in my case it only worsens the quality, the flickering is still ungoing.

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You can try and just disable screen traces all together. If you are hardware raytracing they are not necessary.

r.lumen.reflections.screentraces 0
r.lumen. screenprobegather.screentraces 0
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Hey Shaun, unfortunately this causes the same flickering but creates additional light blinking issues inside of the house:

CVARS:
r.lumen.reflections.screentraces 0
r.lumen. screenprobegather.screentraces 0

have been used for this rendering

Please also check my edit of my original posting as the flickering issue seems to be purely foliage related.
If I delete all foliage, I do not have any flickering even if AA is enabled.

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Ok we can try this cvar
r.Lumen.ScreenProbeGather.ScreenTraces.HZBTraversal.SkipFoliageHits

Or you can just durable Visible in Rayrtacing if you are using Hardware Raytracing. Also set the material to thin foliage / subsurface.

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Hello everyone. I’ve been dealing with this problem for 3 weeks. I downloaded Citysample and when I rendered from there, there was no problem and it was fast. I uploaded my own files to citysaple. I transferred all the lighting-related actors from smallcity_level to my own level. I made some changes and rendered it according to my own design. The problem may also be in defaultengine. It may also be in postprocessvolume. I keep tinkering. But at least he saved the day. I’m sorry my English is a little bad

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