Precomputed Radiance Transfer: Theory and Practice

Siggraph 2005 Course

Jan Kautz      Jaakko Lehtinen      Peter-Pike Sloan

Course Description

Interactive rendering of realistic objects under general lighting models poses three principal challenges. Handling complex light transport phenomena like shadows, inter-reflections, caustics and sub-surface scattering is difficult to do in real time. Integrating these effects over large area light sources compounds the difficulty, and finally real objects have complex spatially-varying BRDF's. Precomputed Radiance Transfer (PRT) encapsulates a family of techniques that partially addresses these challenges. PRT is an active of area of research that has relevance to both the academic research community and practitioners of interactive computer graphics. This technique and its variants are being actively investigated in the game development community and there is quite a lot of interest due to the recent appearance of PRT techniques in games such as "Halo 2".

This course covers these techniques, compares them and discusses their various strengths and weaknesses. A more rigorous derivation directly from the rendering equation is presented along with practical implementation details, both of which are generally not included in technical papers. After introducing the necessary foundation (rendering equation, basis functions, etc.), we begin with simple PRT for diffuse objects. We continue with general PRT using the concept of transfer matrices, which allow for arbitrary reflectance models. The possible choices for basis functions are discussed as well. Different light source representations are presented and compared. Finally, we discuss practical issues with PRT, such as data compression, spatial sampling, normal mapping, precomputation, and more. By the end of the course the audience will be able to pick the right algorithm for their needs and will hopefully have gained some of the unpublished insights the speakers have gained by working in this area.



Jan Kautz, Massachusetts Institute of Technology, Cambridge, USA

Jan is currently a Post-Doc with the graphics group at the Massachusetts Institute of Technology. He received his PhD from the Max-Planck-Institut für Informatik, Saarbrücken, Germany. His thesis was on real-time shading and rendering. He is particularly interested in the realistic shading using graphics hardware, about which he has published several articles at various conferences including SIGGRAPH. Jan has been a tutorial speaker on real-time shading at Eurographics, SIGGRAPH, and others.

Peter-Pike Sloan, Microsoft Corporation, Redmond, USA

Peter-Pike Sloan has been in the DirectX group at Microsoft for the past two years. Prior to that he was a member of the graphics group in Microsoft Research, a staff member at the Scientific Computing and Imaging Group at the University of Utah and worked at both Evans and Sutherland and Parametric Technologies. He is interested in most aspects of computer graphics and most of his publications are available online.

Jaakko Lehtinen, Helsinki University of Technology and Remedy Entertainment, Ltd., Helsinki, Finland

Jaakko Lehtinen is a graduate student in computer graphics at the Helsinki University of Technology, where he received his M.Sc. recently. His research interests span all aspects of realistic image synthesis. Jaakko's interest in graphics stems from working on computer games at Remedy Entertainment, where he has been responsible for design and implementation of radiosity lighting tools and modeling software used in the production of the blockbuster hits Max Payne and Max Payne 2.