Removing Lumen generated ghosting on flat surfaces

This is actually not a question but a guide to users suffering the same problem as I had.

I had some terrible ghosting in my UE5 project, and it very quickly became obvious that its not caused by temporal AA (turned it off, got rid of it from post process settings too, ghosting still appeared)

In the Valley of Ancient demo the environment roughness is fairly high, and rocky so this visual artifact is not visible.
However, if you set up a scene with lumen and the floor surface has a much higher reflectivity (around 0.2 - 0.5) you will see incredibly distracting ghosting if your pawn moves faster than the default walk speed. Maybe even at the default walk speed, haven’t tried it.
I’ve digged deep into the project settings of the Valley scene, and found that what is responsible for the ghosting is Lumen, and they way you can tweak it to your liking is by adding the a line to your DefaultEngine file in the config folder.
This is the one:

in my case it was best around 0.3, it depends on how your floor (or other surface) reflectiveness is set up. Now this on the other hand generates some unwanted noise since lumen is now not really considering those surfaces to trace.
A workaround to find a happy balance is you can increase the Lumen final gathering quality (to 2 or maybe 4) which gets rid of most of the noise. This process is not really affecting the performance since you counterbalance the lower tracing with higher quality final gathering - my project stayed at the same framerate as it was before.

I hope this helps someone!

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Thanks for this, yeah. I had a lot of ghosting problems with flat reflective surfaces and Lumen.

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Got super excited to solve my ghosting with your awesome topic but discovered that my ghosting isnt coming from lumen…neither from antialising or post process. And it is enormous…anyone has another hint what else could I try? thanks!

Sup folks, i’d just like to chime in here (and on other similar posts ive found) in case it helps someone else (as i also tried finding a solution to this).

TLDR: Upgrade / Downgrade your nVidia drivers until you find a version that does NOT produce ghosting. Good for devs? Yes. Bad for end player / customers, as you have to “force them” to use a certain driver version to run your game as intended? Yes…
516.59 = Zero ghosting
527.56 = Extreme ghosting

For me, i had EXTREME ghosting, i’m talking 2 centimeters (real life scale on my monitor) of ghosting from a mountain in the distance against the horizon).

I knew this was peculiar, because i had only noticed it after i built the game my first time, and checked my old dev footage and didnt notice any ghosting at all.

Re-recorded a snippet, to see if it appears in footage, and yes it did.

So what was changed after a long hectic workday where its easy to lose track?

  1. Installed Visual Studio 2022
  2. Installed new nVidia drivers

Yes, it was the new nVidia drivers.
Previous drivers 516.59 = Zero ghosting, even when moving the camera fast.
New drivers 527.56 = Extreme ghosting. Nothing else changed, no nvidida settings changed.

Have you checked disabling Temporal Super Resolution?