Approximate Reflectance Profiles for Efficient Subsurface Scattering

Per H. Christensen, Brent Burley


We present three useful parameterizations of a BSSRDF model based on empirical reflectance profiles. The model is very simple, but with the appropriate parameterization it matches brute-force Monte Carlo references better than state-of-the-art physically-based models (quantized diffusion and photon beam diffusion) for many common materials. Each reflectance profile is a sum of two exponentials where the height and width of the exponentials depend on the surface albedo and mean free path length. Our parameterizations allow direct comparison with physically-based diffusion models using the same parameters. The parameterizations are determined for perpendicular illumination, for diffuse surface transmission (where the illumination direction is irrelevant), and for an alternative measure of scattering distance. Our approximations are useful for rendering ray-traced and point-based subsurface scattering.

Additional materials: [approxbssrdfslides.pdf], [SIGGRAPH_Tech_Talk.pdf]

Available as Pixar Technical Memo #15-04