Problems getting metallic PBR (with blending to non-metallic dirt) to look good

Niber

Probably the biggest obstacle I've had since converting to PBR is that I just can never get a good MatLayerBlend_Standard between a metallic material to a non-metallic (for example rust overlay).

If I make a simple rust material it blends just fine with any non-metallic surface, but the moment I try to blend it (using anything but a super sharp mask) on anything metallic it's a nightmare, I get a white halo around the dirt.

I think it's because metallic has a very high BaseColor (needed for its reflectiveness), so when the blending is blending between 0 metallic and 1 metallic that white basecolor is reaking havoc during the transition. A kind of "pre-mutiply alpha" kind of thing.

I usually try to pre-darken the basecolor around the reveal, but that's getting expensive and still not getting good results.

I don't think this is a UE4 bug, I think it's either an unavoidible flaw with PBR in general or hopefully something that some genious have found a workaround for. Does anyone know?

Obscura

From:
https://www.marmoset.co/posts/pbr-texture-conversion/

Niber

Wow thanks for the quick answer, that's exactly the problem I'm having, so nice to see that it's not just me (UDN support says I'm the only one having this problem and that I need to learn the basics).

quite shocking however that the article concludes that it's an unavoidable problem with PBR, I'm shccked how the whole industry is supposed to transition to this new method if it has this unavoidable artifact. 

I will experiment if I can use the spec workflow on a case by case basis on materials where I have this problem (although if someone does know a PBR-friendly workaround to minimize the artifact please do tell!)

Niber

Oh, turns out you cannot use Spec workflow in UE4 (even if you put spec to 1, that spec has builtin fresnel)

Oh well, now that I use the keywords in your post "edge artifacts PBR" I can see that many threads discuss this issue already

JordanN

Niber said:

quite shocking however that the article concludes that it's an unavoidable problem with PBR, I'm shccked how the whole industry is supposed to transition to this new method if it has this unavoidable artifact. 

I do CGI rendering now but UE4 introduced me to the metal workflow. 

I haven't run into the artifact problems despite using same workflow. I wonder if it's just a current limitation of real time rendering? 

CupMcCakers

What about using power nodes to adjust the falloff of the mask separately for the base color and the other parameters? It probably won't be flawless but you might be able to reduce the artifact to the point where it is no longer noticeable.