Hey guys, I’ve decided to switch back from Lumen (which drove me crazy) to Lightmass and try out GPU Lightmass. Unfortunately, I’m experiencing severe banding and splotches, although the settings should be okay. All the objects I’m showing here had a lightmap size of 4096. Any suggestions?
After thinking the settings were too low the whole time or something was wrong with the mesh, I found out it’s the f-ing denoiser.
One image is denoised at the end of a full build, the other is denoised during “bake what you see.” A significant difference.
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I tried setting the denoiser to ‘during interactive preview’ with a full build. Unfortunately, that didn’t yield any results.
GPU LightmyASS
“This makes the actually great feature almost useless. Does anyone else have an idea of what I can do?”
hi @darstellungsart ,
Your problem sounds similar to the one found/patched in
Thank you for the answer.
I’ve installed and tested the fix, but unfortunately, it still looks the same as before.
So, it didn’t help, unfortunately.
I tried to brute force the whole thing with extremely high settings and without a denoiser. In doing so, I noticed that it still looks like crap. However, it then looked more like compression artifacts. So, it’s not the denoiser but the lightmap compression. When you turn this off, everything looks normal again, even with denoising.
Nice now it does this.
Can this f*cking engine for once just do what it supposed to do?
I just stumble from bug to bug to bug in this program.
Now i can choose if it looks like sht and good while moving or good and like sht while moving.
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Most likely mips being streamed in from using streaming virtual texture lightmaps. You can disable it in project settings (afaik it’s typically disabled by default)
Also I know that you’ve attributed the banding to the denoiser but lightmap compression can also create banding. Should be noted though that disabling lightmap compression will increase the GPU memory cost of the lightmaps.
It’s always tempting to assume that when something is behaving in a way you don’t expect, that it must be a bug. I’ve been in this boat many times myself. Usually though, the simple explanation is that I just don’t understand how the tool works…
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I would have guessed that too; however, I can’t turn it off because for GPU Lightmass, this feature must be activated compulsorily.
Sometimes there are things that don’t work as they should based on pure logic. While it’s not a bug, it’s just poor design. However, in cases like this, where no version or setting leads to a satisfactory result and it’s unmistakably evident that an option doesn’t function as intended, it can indeed be called a bug. In this case, the compression should definitely not have such a strong negative impact. If you disable compression, texture streaming should certainly not appear like that. So, if being a developer is necessary to fix these issues, it’s a bug.
This is not true.
Wow, that’s correct. Okay, then Epic’s documentation is simply wrong. Here, in black and white, it says that it has to be turned on.
[Link to the Unreal Engine documentation page: GPU Lightmass Global Illumination | Unreal Engine 4.27 Documentation]
Open the Project Settings window from the Editor > Project Settings menu:
- Under the Engine > Rendering category, enable the following:
- Ray Tracing > Ray Tracing
- Virtual Textures > Enable Virtual Texture Support
- Virtual Textures > Enable Virtual Texture Lightmaps
I do agree that this could be made more clear in the setup steps that this is optional and only necessary for the realtime preview, but it is there.
Hi @darstellungsart
from the UE 5.3 documentation NOT the 4.27? documentation
GPU Lightmass Global Illumination in Unreal Engine | Unreal Engine 5.3 Documentation
GPULM does not require the Virtual Texturing system to be enabled to simply build lighting but does require it for the interactive and real-time editing functionality. If you do not intend to use virtual texturing in your project or do not require interactive preview, you can forego enabling these and save some overhead while working in the editor.
Sorry about picky with version of documentation, but so much has changed between 5.1 and 5.3 documentation.
Lightmass compression is missed out completely!
Many developers, including me, have had problems with the early documentation. UE 5EA was the worst 
After some testing, there is no direct solution, only a workaround.
The compression of the GPU lightmass looks terrible and can only really be used for mobile applications where you can’t see the details.
So if you turn off compression, everything looks better.
However, you will then use more VRAM.
IN ADDITION, the virtual textures are no longer fast enough to load the lightmaps.
Therefore, you also have to turn off the virtual textures completely. This means that all textures that use VT prevent the project from being packed and you have to check all materials to make sure this does not happen.
Bonus tip: If you now use raytracing reflections, you also have to turn off Nanite, as Nanite is not compatible with raytracing reflections.
So it would be really cool if UE developers didn’t just add new features, but also made sure that certain features work together… or work at all.
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