Subsurface scattering

Subsurface scattering is important for realistic 3D computer graphics, being necessary for the rendering of materials such as marble, skin, leaves, wax and milk.

In reality, many materials are slightly translucent: light enters the surface; is absorbed, scattered and re-emitted – potentially at a different point.

Paths may be terminated inside the material when they reach a contribution minimum threshold or a maximum iteration count.

When a path (ray) hits the surface again, it is used for gathering radiance from the scene, weighted by a lambertian distribution, as in a traditional path-tracer.

The scene is rendered from the light's point of view into a depth map, so that the distance to the nearest surface is stored.

Similarly, depth peeling can be used to account for varying densities beneath the surface, such as bone or muscle, to give a more accurate scattering model.

As can be seen in the image of the wax head to the right, light isn't diffused when passing through object using this technique; back features are clearly shown.

[citation needed] As noted at the start of the section, one of the more obvious effects of subsurface scattering is a general blurring of the diffuse lighting.

[citation needed] A major benefit of this method is its independence of screen resolution; shading is performed only once per texel in the texture map, rather than for every pixel on the object.