SSS Materials and Depth Map Shadows (Maya 2011, Mental Ray)

#1

I’m currently creating a character with hair and I’m experimenting with integrating the hair into the scene in one render. This means using the rasterizer. It’s going well so far. Final gather works and the SSS effects look as they should, but with one small problem.

I’m using detail shadow maps for the direct lights. If I increase the softness of the shadows, something goes wrong with the SSS shader. It seems like the inner mouth geometry is getting hit by the light even though it’s supposed to be in shadow.

With a harder shadow, it doesn’t seem to be a problem. It does get progressively worse as the shadows get softer, though.

Here’s the image with soft raytraced shadows for reference.

Does anyone know how to fix this? Thanks.

#2

My guess is you’re just pushing depth map shadows too far. They don’t work well when they are blurred as much as you are blurring them. There’s light leaking everywhere. Is there a reason you are using them instead of raytraced shadows? Personally I would just go with raytraced. They look infinitely better in this case.

#3

Hi. I was using depth map shadows because I was trying to see if I could get the hair integrated into the scene in a single render. I’m new to rendering hair so I’m still developing my workflow. When I did a fully raytraced test render at full res for reference, it took over an hour to complete.

What I have working now is to have separate passes for the hair and the character. The hair’s cast shadow is raytraced, but at a fraction of the strand count, with much thicker strands and with no transparency. It looks decent in stills, but I don’t know how well it will hold up in animation, especially in close ups.

#4

Fair enough, I assumed it wouldn’t take so long for your render with raytraced shadows. It probably can be optimised a bit but I guess splitting the hair into its own pass will work fine.

#5

You may find some ideas how to render hairs separately here http://kiryha.blogspot.com/2010/06/rendering-fur-with-mental-ray.html

But all this stuff require a lot of human job, so i would better rely on long render time with raytrace shadows with unified sampling. Use mentalcore if you can, will save your time.