V-Ray SSS test.

February 4, 2013

Just testing Vray’s SSS shader for realistic skin look-dev purposes.
I ended with the theory that would be quite simple to set-up a nice, realistic and cheap SSS shader for human and creature assets. I love the raytraced solid scatter, but with complex models I can’t get rid of some of the artifacts in the SSS channel.
I will post more quite soon.

- To achieve better results, I like to combine SSS shaders with Vray Mtl shaders which have better solutions for speculars and reflections. With this method the reflection of the surface is controled by BRDF instead of the poor spec control of the SSS shader.

Do not use Maya Linear Workflow render option combined with Renderman Exposure controls. If you do that your renders will have double gamma correction.
The best option so far should be correct the render using Renderman Exposure controls and gamma corrections for the color textures as usual, and leave the Maya render options as default (sRGB).
Thats it, keep it simple :)

- Corrected render, with Renderman Exposure 1,6 and texture gamma correction as .625

- Uncorrected render, which  means Renderman Exposure 1.0 and no gamma correction for the textures at all.

Yes I know, when we are working with linear workflow and hdri environments in any 3D package, is quite tedious to keep the consistency of our textures. Sometimes they look washed, sometimes they are dark or tinted by some strange colors…

The problem usually comes because the textures are multiplied by the lighting information which comes from the hdri environments, and we need to compensate that, because we are adding information to our textures that should not be there. That’s called normalize textures.

I’m writing here a simple and quick way to fix that problem. Please let me know you thoughts.

- Create an image based lighting setup.

- Create a new plane and assign to it a new mia_material_x_passes completely white with no reflection at all.

- Do a render and configure it as linear.

- Create another mia_material_x_passes with a gamma corrected texture map and assign it to the plane.
- I’m using this simple texture map.

- If you do a render you will realize that doesn’t looks correct, thats because the texture is multiplied by the lighting.

To fix that:

- Apply again the white shader to the plane.
- Bake the lighting information.

- We have to divide the texture by the lighting to normalize the texture.
- Connect the gamma corrected texture to the input 1 of the multiply/divide node.
- Connect the baked .hdr texture to the input 2 of the multiply/divide node.
- Set the operation to divide.

- Render again and the plane should be looking as it should be.


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