Selective compression of lightmaps


we are facing issues with our projects connected to the lightmap compression that UE4 uses. DXT5 compression is - excuse my language - crap when it comes to large, uniformly colored surfaces. We are doing Viz-work with the engine and thus there are plenty of large, white walls in our scenes. Sure there is lighting and all that, but on the walls are visible artifacts (pixelated errors - see image pixelated artifacts) Those artifacts remain no matter what build-quality is used (from preview to production to crazy custom settings)
There is a walkaround - we simply deactivate the lightmap-compression by ini-variable. Works great…

But there is a huge drawback - filesize
Our mapsize and - even more important - the amount of VRAM needed to play our scenes is getting to problematic regions. Our current project uses about 1.6GB of memory-poolsize when played…with compressed lightmaps the memory consumption decreases to around 1GB…so it’s a very noticeable effect.

What i’d like to know now is…is there a way to have some sort of selective lightmap compression? I’m for example completely ok with the compression on most objects in my scene, but i’d like to be able to turn it of for specific objects, where artifacts would be clearly visible (e.g. large walls in shaded areas)
I know, that you can look into the built lightmaps under world-settings/lightmass…but how shall i know, which lightmap belongs to which object? And how can i make sure, that the chosen compression (or no compression in that case) persists after a rebuild of the lighting?

So…is there a way to more precisely influence the compression of lightmaps? Or maybe…could there be a way for that in the future? It would really help us out and i think it would also help others doing more “serious” work with the engine. I don’t mean that in a disrespectful way but more in a way that means, that games are often times more vivid and alternating in their surfaces/textures wheres classic visualisation style consists of many plain colored surfaces where compression artifacts are clearly visible.!

Hello there!,

I am having the same issue and i cannot find the way to fix it.

Did you find the solution? I would really appreciate if you could help me.


Im also interested in this solution :slight_smile:

This is something I would love as well. There are a few architectural flat surfaces that really show the compression artifacts, and it would be a huge improvement to isolate those and disable compression.

Second that too. Making VR-archvis without such feature is pain. If there was a way to just direct meshes into atlas groups with individual options for each group, that’d be perfect.