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Global Illumination: Radiosity, Photon Mapping & Path Tracing

A comprehensive overview of global illumination techniques, including radiosity, photon mapping, and path tracing. Explains the concepts, algorithms, and applications of these methods in computer graphics. Covers the latest developments and future trends in the field.

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Global Illumination: Radiosity, Photon Mapping & Path Tracing

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  1. Global Illumination:Radiosity, Photon Mapping & Path Tracing Rama Hoetzlein, 2009Lecture NotesCornell University

  2. Global Illumination Consider all energy moving in a space, not just the light that reaches the eye.

  3. First used in the study of Heat Transfer (1950s), how does energy move around a room or object.

  4. Radiosity First used in Computer Graphics, 1984 Modeling the interaction of light between diffuse surfaces,C. Goral, K. E. Torrance, D. P. Greenberg and B. Battaile. 1984Computer Graphics, Vol. 18, No. 3.

  5. Fij i j

  6. Radiosity Solution One eqn. for each patch

  7. Radiosity - Overview • Each patch contributes energy to other patches • Each patch i has a Radiosity equation: • Solve all equations simultaneously to get the energy at each patch • What is the hardest part of this eqn? Ei = Energy emitted Ri = Energy reflectedFij = Energy on patch I from j

  8. Radiosity - Form Factors What things might contribute to the Form Factor? Remember: Form Factor is amount of energy hitting patch i from patch j

  9. Radiosity - Form Factors What things might contribute to the Form Factor? Remember: Form Factor is amount of energy hitting patch i from patch j • Size of the patch Bigger = more energy • Angle between patches Direct = more energy • Dist. between patches Father = less energy • Objects between patches Occlusion = less energy

  10. How much does patch j block patch i ?

  11. Raytracing

  12. Raytracing /w Caustics

  13. Radiosity

  14. Radiosity • Benefits 1. Very realistic (actually computes energy) 2. View independent.. Compute once, then view 3. Effects: Caustics, Color bleeding • Drawbacks 1. Even more expensive than raytracing 2. Cannot simulate mirror reflections !(energy travels diffusely, not coherently)

  15. Hybrid Rendering • Combine Raytracing and Radiosity: • - Radiosity to give energy transfer: Color bleeding Light diffusion Caustics Soft shadows • Raytracing to give view-dependent terms: Reflections Refractions Specular highlights

  16. Lady and Gentleman at the VirginalsJohannes Vermeer (Dutch), 1662-65 Two Pass RenderingWallace, Cohen, Greenberg, 1987

  17. Photon Mapping Instead of computing all patches simultaneously, cast “photon rays” from light source. Uses points instead of patches. Photon Mapping - photons propogate Radiosity – patches don’t move

  18. Photon Mapping - Much faster.. No form factors- Need lots of photons but easier to compute.- Realistic. Photons move the way light does. Two pass approach: 1. Shoot photons around scene 2. Collect photons to create image (nearby photons are smoothed)

  19. Photon Mapping Made Easy, Yu, Lowther, Shene, SIGCSE 2005

  20. Photon Mapping Made Easy, Yu, Lowther, Shene, SIGCSE 2005

  21. Future Trends • Recent Developments (past 5 yrs): • - Ambient Occlusion – Approximation to Photon Mapping • Real-Time Raytracing using GPUs • Hybrid Rasterization and Raytracing • Volumetric Raytracing & Radiosity

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