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Precomputed Local Radiance Transfer for Real-time Lighting Design

Precomputed Local Radiance Transfer for Real-time Lighting Design. Anders Wang Kristensen Tomas Akenine-Moller Henrik Wann Jensen SIGGRAPH ‘05. Presented by Shao-Ti Lee. 2010/04/08. Outline. Introduction Related Work Constructing the Light Cloud Compressing Surface Radiance

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Precomputed Local Radiance Transfer for Real-time Lighting Design

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  1. Precomputed Local Radiance Transfer for Real-time Lighting Design Anders Wang Kristensen Tomas Akenine-Moller Henrik Wann Jensen SIGGRAPH ‘05 Presented by Shao-Ti Lee 2010/04/08

  2. Outline • Introduction • Related Work • Constructing the Light Cloud • Compressing Surface Radiance • Real-time Relighting • Results • Conclusion

  3. Introduction • Related Work • Constructing the Light Cloud • Compressing Surface Radiance • Real-time Relighting • Results • Conclusion

  4. Introduction • MAIN IDEA • Unstructured light cloud.

  5. Introduction • MAIN IDEA • Unstructured light cloud.

  6. Introduction • FEATURES • Local, not distant illumination. • Accurately represent incident radiance on different parts of the model. • Light positions and intensities are changeable. • Lights can be added or removed. • Materials can be glossy. • Camera is fully dynamic. • Scene is assumed to be static.

  7. Introduction • Related Work • Constructing the Light Cloud • Compressing Surface Radiance • Real-time Relighting • Results • Conclusion

  8. Related Work • Precompute the exitant radiance [Wood et al. 2000; Chen et al. 2002] • Basis: sphere harmonics.

  9. Related Work • Sphere harmonics. Approximated Exitant Radiance SH Basis Approximated Exitant Radiance in the SH basis

  10. Related Work • Clustered PCA(Principle Component Analysis) [Sloan et al. 2003] • For geometry data representation compression. Clustering Ex. K-Means PCA

  11. Introduction • Related Work • Constructing the Light Cloud • Compressing Surface Radiance • Real-time Relighting • Results • Conclusion

  12. Constructing the Light Cloud • Before doing this, first divide the geometry into a set of discrete zones using a simple top-down partitioning algorithm.

  13. Constructing the Light Cloud • Use a two-stage approach to construct the light cloud. • Stage 1 Make a sufficiently dense uniform sampling of the region of interest. • Stage 2 The light cloud is then simplified by clustering similar lights using a bottom-up clustering algorithm.

  14. Constructing the Light Cloud This is for point lights.

  15. Constructing the Light Cloud This is for diffuse surface.

  16. Constructing the Light Cloud S A B C Cluster List D E F A B C D E F G S H I G H I Priority queue sorted by △jk △AB △AD △BD △CE ….. Compute △SC , △SD , △SE , △SF , △SG , △SH , △SI and re-sort the priority queue to end a loop and stop until △jk≧1for all j, k

  17. Introduction • Related Work • Constructing the Light Cloud • Compressing Surface Radiance • Real-time Relighting • Results • Conclusion

  18. Compressing Surface Radiance • Before compression • Per vertex matrix X , with np = nb x nlelements per color channel. • nb : The number of SH bases. • nl: The number of lights. • After compression using CPCA weights Cluster Mean PCA vectors (bases)

  19. Introduction • Related Work • Constructing the Light Cloud • Compressing Surface Radiance • Real-time Relighting • Results • Conclusion

  20. Real-time Relighting • Organize the local lights in a kd-tree and locate the m nearest lights.

  21. Real-time Relighting • To avoid undesirable popping effects, set the weight for each pre-computed local light to • After computing all weights, normalization is used. And all weights are multiplied by the powerof the light at l.

  22. Real-time Relighting • Visibility problem Cannot assign weights! Solution: Use ray tracing with a few rays.

  23. Real-time Relighting • Discontinuity Problem Suddenly disappear/appear due to occlusion! Solution: Smoothly fade out/in lights over time, but that now have become obscured by geometry.

  24. Real-time Relighting • Computing Exitant Radiance • For each cluster, xm and bi are constant.

  25. Real-time Relighting • Reconstruct the vector of SH coefficients representing exitant radiance in a vertex program by evaluating • Where is the variable to ensure that we get correct blending at the borders between clusters and between zones. • Recall that

  26. Introduction • Related Work • Constructing the Light Cloud • Compressing Surface Radiance • Real-time Relighting • Results • Conclusion

  27. Results

  28. Results

  29. Results Left: Method of authors. Right: Ray tracing with per pixel lighting.

  30. Results

  31. Introduction • Related Work • Constructing the Light Cloud • Compressing Surface Radiance • Real-time Relighting • Results • Conclusion

  32. Conclusion • The system handles indirect illumination efficiently for models with more than 100,000 triangles. • Future Work • Soft shadow • Spotlight

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