SSS materials with shadowing of intersecting objects.

[LL_Will_J]

Hi Guys,

I have a shot with a baby's hand which is totally backlit. The idea is that we would like to see the bones underneath the skin.

Currently the shader is an ALshader (which is working really well for the look of the skin and SSS).

However when I try to add objects for the bones in the hand I can't get the bones to block the light coming through the skin.

I have created the attached image to clearly explain the problem. But basically when a mesh isnt intersecting the skin it works as expected. But once the mesh is 'inside' the SSS object it stops working.

I would appreciate any help I can get to solve this problem.

Thanks in advance!

Will

[LL_Will_J]

Also - I have tested this with Vray SSS materials and got the same results.

I have seen that a refractive material works - but I think it will be really hard to make a good skin shader with a refractive material.

Thanks again!

Will

[yolov]

Hey, sorry for the late reply.

This is going to be tricky with a single shader.
What you're after is not easy with sub-surface scattering and I'm not even sure that this is possible with AlSurface or SSS2.
Volumes can do this, but not SSS. You can texture the SSS radius, but this is convenient for veins and not bones.

I've been trying to come up with some setup that can mimic this and I think it could work if you blend a refractive VRayMtl on top of ALSurface or SSS2 using a VRayBlendMtl. You can lower the refraction amount in VRayMtl too, but in this case make sure the diffuse is black.
You can also use a falloff texture or a painted texture to blend the refractive material with the sub-surface scattering one.

Another approach would be to render separate passes with a refractive material and a sub-surface scattering material and blend them in post.

I hope that this is something you can use and that other people can chime in with more ideas.

[guillaumelepage]

Maybe you could boolean substract the bones from the flesh. That way there would be no intersection. Assuming it's no being animated. Good luck

[vlado]

In the V-Ray Next nightly builds you can also try a BRDFScatterVolume material for this. It will do actual path traced SSS and should be able to handle this correctly.

Best regards,
Vlado

[LL_Will_J]

Ohhh that sounds cool! We are currently looking to make the upgrade to Vray next asap.

We settled on a comp fix for now. The bones in the hand are rendered as a separate black and white pass that is then used to grade the SSS render element. Its producing nice results. So happy with the solution.

The Boolean subtract could be interesting with a Vray Clipper. Might test that for future projects.