Precomputed Radiance Transfer Field for Rendering Interreflections in

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Precomputation Compression The raw RTF data is quite large 4 th-order SH, 8 - 24 proxies, 16 concentric spheres with 1536(6× 16) directions. —— 192 ∼ 576 MB CPCA (Clustered Principle Component Analysis) The compression ratio is about 40 -50: 1 Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University

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

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

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

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

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

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

Results A PC with Intel Core 2 Duo 1. 8 GHz, 2 G RAM and a n. Vidia 7800 graphics card. Objects Verts RTF size FPS Cornell-box 7 22 K 44. 1 MB 8 -12 Cornell-box dynamic 8 40 K 50. 0 MB 10 -16 Table 4 40 K 32. 8 MB 8 -10 Brick game 10 86 K 63. 5 MB 5 -8 Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University

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 also some limitations. 1. only handle low-frequency interreflections and illumination. 2. only limited to rigid objects. Precomputed Radiance Transfer Field State Key Lab of CAD&CG, Zhejiang University

Thank you!