Research :: Subsurface Scattering

All non-metallic materials are translucent to some degree. This means that light scatters inside the material before being either absorbed or leaving the material at a different location. This phenomenon is called subsurface scattering. Note the soft and smooth appearance as well as the light diffusing through the marble.

True subsurface scattering cannot be simulated using the ubiquitous BRDF (Bidirectional Reflectance Distribution Function). Instead it requires a full simulation of the BSSRDF (Bidirectional Scattering Surface Reflectance Distribution Function). Traditional methods such as monte-carlo integration are quite good at simulating subsurface scattering, but it becomes costly for highly scattering materials such as milk and skin. For these materials it is better to use a diffusion approximation. The diffusion approximation is much faster while remaining fairly accurate. The work in this area is in colloration with Tom Mertens.

Images of translucent object encountered in our daily live

The images presented here are created by Koen Beets and Erik Hubo

A marble block lit from the front. Note the impurities at the left. Marble Marble lit from the side The marble block this time lit the side.
A marble block lit from the front. Note the impurities at the left. Marble Marble lit from the back with shadows generated by a hand The marble block lit from the back with shadows generated by a hand.
Glass of milk. Milk Marble lit by a laser A laser illuminating the marble block.
Glass of milk. Milkglass Milk noticable colorshift Glass of milk lit from above with a flashlight.

A Computational Approach to Simulate Light Diffusion in Arbitrarily Shaped Objects

Buddha

We presented a technique for rendering translucent objects based on the diffusion approximation. This yields a relatively simple partial differential equation, which we propose to solve numerically using the multigrid method. We emply an embedded boundary discretisation to accurately represent the interactions near the object's surface and to avoid inconsistencies. We also allow the simulation to refine hierarchically in order to lower computational and storage requirements. The approach is capable of rapidly and accurately computing subsurface scattering within arbitrarily shaped objects for both homogeneous and heterogeneous materials.

The paper and results can be downloaded here.

last update November 6, 2006