Recently, more details on this technique have appeared in a RenderMan Technical Memo called Point-Based Approximate Color Bleeding, available on Pixar’s publication page. Pixar have implemented an interesting global illumination algorithm based in part on Bunnell’s disk approximation, which is used for transfer over intermediate distances. Spherical harmonics are used to approximate distant transfer and ray-tracing is used for transfer between nearby points. This technique is now built into Pixar’s RenderMan and has been used in over 12 films to date, including Pixar’s own Wall-E. it is interesting to see a technique originating from real-time rendering used in film production; the opposite is much more usual. The paper is worth a close read – perhaps someone will close the loop by adapting some of Pixar’s enhancements into new real-time techniques.

Pixar’s publication page is a valuable resource. The papers span a quarter century, and most of them have been very influential in the field. The first seven papers gave us the Cook-Torrance BRDF, programmable shaders, distributed ray tracing, image compositing, stochastic sampling, percentage-closer filtering, and the REYES rendering architecture (upon which almost all film production renderers are based). the page includes many other important papers as well as SIGGRAPH course notes and Renderman Technical Memos.