RMS 18
Subsurface Scattering

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Related Topic

    a custom cutrSSSMaterials node
    table of DMFP values


This tutorial demonstrates the workflow for rendering objucts using raytraced subsurface scattering (SSS). Figure 1 shows a side-by-side comparison of two dented nurbs spheres (each 1.0cm in radius) with and without SSS.

Figure 1

SSS is very sensitive to object size because the depth to which the red, green and blue components of light will penetrate (dmfp - diffuse mean free path) is measure in mm's. For example, in the case of marble the "penetration" (dmfp) distances are,
    red - 8.51mm
    green - 5.57mm
    blue - 3.95mm.

Step 1 - Adding a SSS Material

1.1     Assign the RMSGPSurface material to the surface(s) that will exhibit SSS.
1.2     In HyperShade right-mouse click the material and choose "Graph Network".


1.3     From RenderMan->Utilities select the custom cutrSSSMaterials node.


1.4     In HyperShade's "Work Area" middle-mouse drag from the cutrSSSMaterials node to the RMSGPSurface node and choose "Other..." from the popup menu.

1.5     In the Connection Editor connect,
          cutrSSSMaterials.albedo to RMSGPSurface.sssAlbedo and,
          cutrSSSMaterials.dmfp to RMSGPSurface.sssDmfp and,


1.6     In the attribute editor for cutrSSSMaterials select a suitable material.


Step 2 - Adjusting the SSS

2.1     In the attribute editor of the RMSGPMaterial adjust,
          "Diffuse Mix" to increase/decrease SSS, and
          "Samples" to improve the quality of the SSS.


© 2002- Malcolm Kesson. All rights reserved.