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4.25.3 - Reflection volume brightness issues

Hi there,

I am having some issues with the reflection volumes (sphere or boxes) rendering wrong brightness on half-rough surfaces. It seems the energy conservation is broken.
At first I thought it was because I was using physically based light intensities, but noticed the same behavior with low unitless intensities.

Here is the problem I see: Screenspace Reflections is turned off, there is only a sphere reflection volume captured inside the room (brightness of 1). I am adjusting the roughness of the material from 0 to 1.
https://youtube.com/watch?v=qeneKrshIq4

You can notice how the reflection becomes brighter than the environment when the roughness is around 0.25 - 0.3. In case you would be wondering, the sky above is not brighter than the visible sunrise, so there is no real reason for it to become brighter.
3ON1s0QAP6.jpg

As a comparison, here is the same using screenspace reflections (max roughness of 1). You can see how the energy is more accurate as I change the roughness.

https://www.youtube.com/watch?v=aRtl9-pl4_Q

Another oddity is that if I turn the reflection volume brightness to 0, it still brightens the environment a lot. I need to turn off its visibility to make it not affect the environment. Is that the expected behavior?

brightness1.jpg
Brightness 1

brightness0.jpg
Brightness 0 - Only a tad darker.

invisible.jpg
Visibility OFF

Finally, I noticed that overlapping reflection boxes would lead to darkening of the reflections. One volume doesn’t get priority over the other one, it just makes the overlap area darker.
overlap.jpg

I tried to reproduce these issues in the ContentExamples project but it seemed to work fine. I looked into my Project settings I tried turning on and off “Extend default luminance range in Auto Exposure settings” as this was one of the setting I had changed in my project. Otherwise everything is default. But this didn’t help.

Has anyone encountered the same problems?
Thanks!

https://github.com/EpicGames/UnrealEngine/pull/6425
There is at least this bug with reflection captures.

Thanks Kalle. It’s a bit sad to see that your fix from Dec 2019 hasn’t been merged. I don’t know if that would fix all the issues I encountered, but this just means reflection volumes aren’t really reliable :frowning:

The problem seems to come from the skylight. It is set to capture the scene with a brightness of 1, but the reflection is too bright.
90045d4c3abe8931808f43aa2ec8d439fc286302.jpeg

I changed my HDRI skybox from movable to static so it is captured by the reflection volumes, and it fixes the brightness issue (it’s still a tiny bit brighter than SSR results but it’s acceptable).
e5034817051adf55e3dc62a614f536f3280a4ac3.jpeg
https://forums.unrealengine.com/core/image/gif;base64