[SOLVED] UE4 lighting artifact issue - strange bright spots on static mesh

CrackRockSteady

Hello!  Hopefully someone here can help me out with this lighting issue I'm having, I've tried everything I can think of to fix this to no avail.

Everything in the scene is baked lighting, I'm running 4.18, the problem i'm having is a bright spot that appears on a shadowed part of the mesh, but the spot only appears when viewed from a distance.



When I move a bit closer to the object:


Lighting Only view mode:


The only thing I can find when trying to search for this is people having issues with light bleeding but I don't think that's the issue here.  The bright spot isn't on a UV seam and I've tried baking this with my own lightmap UVs and Unreal's auto generated UVs:


I've tried baking with lightmap res from 32 to 1024, doesn't seem to make any difference.

I thought it might be a smoothing issue with the mesh so just for fun I turbosmoothed it a couple times and re-baked, no dice.

I've also tried various Lightmass adjustments but tbh I haven't done any lighting in Unreal for a long time and I'm not super familiar with it, so if anyone has any ideas please let me know!  Thanks.

Edit:  Lightmass settings:



I tried making adjustments to Indirect Lighting Quality and Indirect Lighting Smoothness but there was no effect on the spot.

Obscura

Could be mip map. In the static mesh, you can set the "minimum lightmap res". Try increasing that.

CrackRockSteady

@Obscura gave that a shot just now, tried baking with it set to 64, 128, 256, same results each time

Obscura

Too bad...Then you can try this, but it will affect multiple objects, not only this one. Go to the world settings, and go to the lightmass section there. You'll see the array of baked lightmaps on the bottom section - its also visible on your last picture. Find the one that belongs to this object, and either disable mipmaps, or change the generation method to be sharpen for example.

CrackRockSteady

@Obscura Thanks for your reply, I'll give it a try tonight when i get home!

CrackRockSteady

I wasn't sure which lightmap was for this asset so I changed the setting on all of them just to be sure.  I tried disabling mipmaps first and then tried changing them all to Sharpen but I am still getting this bright splotch.

I'll keep poking around with it and see if I can figure it out.

JordanN

In the past, I've used lightmass importance volumes to help garner better accuracy in lightmap baking. Especially if you're doing a big level, the engine will shoot photons everywhere and in some areas it may be alright, but in others it goes crazy.

If you also haven't done so already, you can edit the base .ini files and crank up the internal lightmass settings. Renders will take longer, but it will get you closer to Vray/Archviz like results.

CrackRockSteady

@JordanN I am already using a lightmass importance volume.  I'd rather not go overboard with the lightmass settings.  I'm looking for what's causing the issue and a more realistic solution than going crazy with the settings.  Even increasing the lightmap resolution was only intended as a way to determine what was causing the problem.  If setting the res to 1024 had fixed the bright spot I would still need a better solution but at least I'd know it was a lightmap issue.

I managed to get rid of the spot by slightly adjusting the angle of my main directional light.  Still not sure what was causing the issue but at least it's gone for now.

If I figure out anything else as I'm working on this I'll be sure to post an update.

Obscura

Are you using stationary directional light with cascaded shadows? I was only able to reproduce this kind of resolution change over distance, using these.

CrackRockSteady

@Obscura I had to go look up what cascaded shadows were and then check my scene (like i said, not super familiar with UE4 right now).  My light was using cascaded shadow maps.  I set the dynamic shadow distance to 0 to disable it and it immediately fixed the problem.  Thank you so much!

Obscura

Great. I think in a scene where the sun condition cannot change, you should rather go with static movability. Reflection quality can be worse though... So I guess its up to your consideration, but if you take a look at the profiling tool, you can see that cascaded shadows are more expensive than static ones.

CrackRockSteady

Yes I think you're right, for my purposes that will work best.  

Happy to have been able to learn something, thanks a lot for helping me out with this I was pulling my hair out.