Lines with random walk SSS

Artistic Support Materials and Textures
1

Wasn’t sure whether to post this in tech support or here.

Any idea what’s causing the following:

shade flat
shade flat1048×1323 750 KB

Shade flat, as expected the subdiv “lines” are visible in cycles. This is also with SSS on.

shade smooth
shade smooth1048×1323 696 KB

Same settings but shade smooth is on, the “subdiv” lines are still very visible as some kind of SSS artifacting. In some places depending on how quads are tesselated into triangles, the problem is very noticeable.

shade smooth no SSS
shade smooth no SSS1048×1323 642 KB

Shade smooth with no SSS, shading looks what I would expect it to.

The issue seems to happen only with Random Walk SSS, Christensen-Burley looks like what I would expect. The topology is not perfect probably, that’s whatever, but usually shade smooth can still “patch” over the shading when there are no rough 90 degree angles. Indeed as said, without SSS shade smooth works fine, and with CB SSS it looks fine as well.

I don’t want to say this is a bug or anything, does Random walk need denser geo or something, as adding more subdiv levels does seem to help a little, but it might also “dither” the lines to the material so as to not make it visible.

2

Random walk does volume scattering. With a lightly subdivided mesh, every edge near the terminator line is essentially a small ridge that predictably catches light moreso than the surrouding area. Same as it would do in reality.

Try increasing subdivision level!

3

Fair enough, the current mesh is about as sparse as I could retopologize it. I have to add three levels of subdiv to get rid of the most egregious of lines.

Doing some more searching online I did figure that the mesh is not really in well enough shape to actually work with the random walk algorithm. The lips for example which do intersect create an overlapping volume that the algorithm just cannot solve.

Thanks for you help!