Screen space ambient occlusion banding issue

David Junghanns
Tue, 31 Aug 2021 08:00:47 +0000
Rendering

I’m having trouble with a disruptive artifact in my screen space ambient occlusion.

All meshes regardless of lighting, material or level have strange banding across them, along with the “regular” ambient occlusion. In all these screenshots, the AO is increased to darker than normal values to make the issue clearer.

Here is the AO buffer visualization to make the artifacts a bit clearer:

The shape of these artifacts look like they get caused by planes stacked in front of the viewport camera, spaced further apart the further away from the camera they are. The artifacts are also view-angle dependent, being more easily visible on faces parallel to the camera plane.

Here are the settings of the only post-process volume in this level. The Intensity has been increased temporarily to see the issue more clearly, changing the radius only changes the contrast of the bands. They do disappear at small radius values (<2), however these values are impractical, since they remove all other AO as well.

I’ve tried numerous things to fix this.

Playing around with settings in the post process volume only alters the appearance of these bands without removing them

Creating a new, completely empty level still has the banding in the AO on all objects, even UE4 basic cube actors

Baking all lighting does not fix the issue, nor do unbaked meshes look any different from baked ones.

Luckily there is one workaround I’ve discovered working so far, pulling the AO falloff incredibly close to a distance where the planes stacked in front of the camera are so close that the effect disappears. This of course removes AO from distant objects completely, so I’d rather find an actual solution. Replacing SSAO in favor of DFAO will sadly not work for this project either, as all meshes are set up to be baked.

Any pointers will be appreciated!

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