Precomputed Radiance Transfer Field for Rendering Interreflections in Dynamic Scenes Minhao Pan, Rui Wang, Xinguo Liu, Qunsheng Peng and Hujun Bao State Key Lab of CAD&CG, Zhejiang University, P.R. China 23/7/2007

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Related works Traditional global illumination methods Based on ray-trace or radiosity Realistic but slow Precomputed light transport Static scene —— PRT[Sloan, 2002] Shadow in dynamic Scene ——[Zhou, 2005] Interreflections in dynamic scene ——[Iwasaki, 2007]

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Interreflection Transfer Function (ITF)

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Interreflection Transfer Function (ITF) Environment Lighting [Sloan, 2002]

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Interreflection Transfer Function (ITF) Environment Lighting [Sloan, 2002]

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Interreflection Transfer Function (ITF) Local lighting

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Proxy-based incidient light approximation

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Proxy-based incidient light approximation The incident light to p

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Proxy-based incidient light approximation Local lighting

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Proxy-based incidient light approximation Local lighting

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Proxy-based incidient light approximation Local lighting

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field Proxy-based incidient light approximation Local lighting

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Radiance Transfer Field

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Precomputation Compute radiance transfer on each vertex Compute radiance transfer on samples in field Compress the radiance transfer field

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Precomputation Compute radiance transfer on vertices

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Precomputation Compute radiance transfer on samples in field

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Precomputation Compression The raw RTF data is quite large 4th-order SH, proxies, 16 concentric spheres with 1536(6×16×16) directions. ——192 ∼ 576MB CPCA (Clustered Principle Component Analysis) The compression ratio is about 40-50:1

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field A two-level scheme Bouncing Step accumulate interreflections between objects Rendering Overview

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field A two-level scheme Bouncing Step accumulate interreflections between objects Shading Step compute the final shadings on vertices. Rendering Overview

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Rendering Bouncing Step Iterative bouncing strategy In one iteration: For proxy q in bunny 1. compute the interreflections from proxy q k 2. sum all interreflections from other proxies

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Rendering Shading Step One pass. For each vertex: 1. compute the illumination from proxy q k 2. sum all illumination from proxies 3. standard PRT process

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Rendering Caching strategies Caching RTF samples Store incident light at samples. Caching RTF eigens By using CPCA, we can store the product of eigens and the incident light of proxies. ——hit rate > 95% and reduce the cost > 90%

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Results Comparison Our approachReference

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Results A PC with Intel Core 2 Duo 1.8GHz, 2G RAM and a nVidia 7800 graphics card. ObjectsVertsRTF sizeFPS Cornell-box722K44.1MB8-12 Cornell-box dynamic 840K50.0MB10-16 Table440K32.8MB8-10 Brick game1086K63.5MB5-8

State Key Lab of CAD&CG, Zhejiang University Precomputed Radiance Transfer Field Conclusion and future work Contributions: 1. Radiance transfer field 2. A proxy-based approximation method for precomputed RTF 3. An efficient interreflection rendering algorithm using precomputed RTF There are also some limitations. 1. only handle low-frequency interreflections and illumination. 2. only limited to rigid objects.

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