Setting Up Sub Surface Scatter (SSS)

This tutorial covers how to set up a basic SSS Mental Ray shader.

Set-up

Download and open example.mb.

Set the menu set to rendering.

Go to window>rendering editors>render settings.

Set the "render using" to Mental Ray.

Go to window>rendering editors>hypershade.

For more on using the hypershade, read this tutorial. Link

Sub Surface Scatter (SSS)

Sub surface scatter allows light to pass through a shader. Example: A lamp shade. Sub surface scatter is commonly used when rendering cloth, human skin, and anything else that needs to be soft and thin and light can pass through it.

Sub surface scatter can only be used in Mental Ray, but there are some ways of faking sub surface scatter (not covered in this tutorial). Sub surface scatter need firsts a Mental Ray SSS shader, second a light map shader, and last a Mental Ray file to store the data in.

Creating The Shader

Step one - In the hypershade, go to create>Mental Ray materials>misss_fast_shader.

Step two - Select it in the hypershade and open the attributes editor (window>attributes editor).

Step three - First we're going to set-up our Mental Ray texture to save the SSS information. Roll down to data storage and go to lightmap. Click on the checkerboard and Maya will create a new Mental Ray texture and connect it to the lightmap attribute of the shader.

Step four - First check "writable". Now we need to set the resolution of the file that it will write. This is supposed to be twice the size of your final rendered resolution. Example: You're rendering your scene at a resolution of 640x480, so your file resolution should be 1280x960. Set your file size depth to 32 bits. This has to be set to 32 bits or the entire effect won't work.

Setting Up The Light Map Shader

The lightmap shader needs to be connected to the shading group, so its a good idea to "graph network" the shading group before proceeding.

Step one - In the hypershade, go to shading groups and select misss_fast_shader1SG. Right click and select "graph network".

Step two - With the shading group selected, look at its attributes in the attributes editor. Click on the Mental Ray tag and go to custom shaders.

Step three - In the light map shading slot, we're going to connect a misss_fast_lmap_maya shader. Click on the checkerboard to open the create render nodes window. Go down to light maps and select misss_fast_Imap_maya.

Step four - Select the new shader in the hypershade and open the attributes editor.

Step five - Go to the tag lightmap write. The lightmap field is where we're going to connect our light map texture. To do this, middle mouse button drag the Mental Ray texture into the attributes editor and drop it onto the field.

Assigning The Shader To The Model

Now that the shader's created, let's assign it to the model.

Step one - Select your model (if you're using the example model, it's the sphere).

Step two - In the hypershade, right click on the misss_fast_shader and select assign material to selection.

Now take a test render. You can see the point light behind the sphere that we created shining through the sphere.

Tweaking The Shader

Re-select the shader and open the attributes editor.

Let's go to algorithm control.

Step one - First we need to get rid of all that noise in the rendering. Go to samples and increase the samples to something like 1000.

Step two - We want to increase the spread of the SSS effect. To do this, increase the radius attribute of the back SSS radius. Set it to 20.

Step three - Now roll up to optical properties.

Diffuse shader - You can connect a different shader to define the diffuser properties. Example: You have all the same effects from the SSS, but with a mia_material diffuser.

Diffuser - This works like any other shader. It's the general color of the shader.

Diffuse weight - This is how much affect the diffuser will have on the overall shader.

Specular shader - Works the same as the diffuse shader, but this is one is specular.

Front SSS color - This is the color of light that enters the front of the shader.

Front SSS weight - This is how much this color will affect the shader.

Back SSS color - This is the color of the light that comes through the back of the surface.

Back SSS weight - This is how much the back SSS color will affect the shader. Example: If you set this to 3, the SSS effect would seem intensified.

Final Notes

For SSS to work, the surface needs to have thickness (geometry on the front and back on a model).

The front and back on an SSS shader are defined by the camera angle.

Almost all attributes can have a texture map connected to them: diffuser, SSS color, SSS weights, etc.

Conclusion

I hope this tutorial's taught you the basics of setting up SSS in Maya. Good luck.