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05 ’ Digital Image Synthesis Presented by Jen-Yuan Chiang

Efficient Simulation of Light Transport in Scenes with Participating Media using Photon Maps - Henrik Wann Jensen Per H. Christensen. 05 ’ Digital Image Synthesis Presented by Jen-Yuan Chiang. Issues addressed by the paper. Realistic Volume Rendering

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05 ’ Digital Image Synthesis Presented by Jen-Yuan Chiang

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  1. Efficient Simulation of Light Transport in Scenes with Participating Media using Photon Maps- Henrik Wann JensenPer H. Christensen 05’ Digital Image Synthesis Presented by Jen-Yuan Chiang

  2. Issues addressed by the paper • Realistic Volume Rendering • The ability to simulate following effects: • Multiple Volume Scattering • Color Bleeding between volumes and surfaces • Volume Caustics

  3. Multiple Scattering • Single Scattering • Multiple Scattering

  4. Color Bleeding Without participating media With participating media

  5. Caustics • Surface Caustics Light reflected from or transmitted through one or more specular surfaces strikes a diffuse surface.

  6. Caustics • Volume Caustics Light reflected from or transmitted through specular surfaces and then scattered by a medium

  7. Issues addressed in this paper • Extends the method of photon mapping to achieve the global illumination of scenes with participating media

  8. Outline • Overview of Photon mapping for surfaces • Light transport in participating media • Extending Photon Mapping to Participating Media • Results

  9. Overview of Photon Mapping for Surfaces • Global Illumination technique • Two-pass particle-tracing algorithm • First pass: • Building the photon maps using photon tracing • Second pass: • Rendering using these photon maps

  10. First pass • Photons emitted from light sources • Simulate the transport of each photon • Store photon in photon maps when it hits nonespecular surfaces • Direct map • Caustics map • Indirect map • Balanced kd-tree is used to handle photons

  11. 3 photon maps Ex. LSSSDSSSSD Caustic map Indirect map

  12. Second Pass Specular reflection Direct Illumination Indirect illumination Caustics

  13. Second Pass • Illumination at a point is divided into four parts • Specular reflection: ray tracing • Direct illumination: direct map or ray tracing • Caustics: caustics photon map • Indirect illumination: indirect photon map

  14. Radiance Estimate • Information of Photons • Position(p), power( ), incoming direction( )

  15. Outline • Overview of Photon mapping for surfaces • Light transport in participating media • Extending Photon Mapping to Participating Media • Results

  16. Light Transport in Participating media p q Radiance L changes continuously from L(p,w) to L(q,w)

  17. Volume Scattering • Emission • In-Scattering • Absorption • Out-Scattering Scattering coefficient Absorption coefficient

  18. Volume Rendering Equation Extinction coefficient Ray marching

  19. Ray Marching • Computes the contribution from the medium by dividing the ray into smaller segments X0 X1 X2 Xk emission in-scattering extinction(assuming medium properties are the same through )

  20. Outline • Overview of Photon mapping for surfaces • Light transport in participating media • Extending Photon Mapping to Participating Media • Results

  21. Extending Photon Mapping to participating media • From for surfaces to for volumes • Still 2 pass particle tracing algorithm • First pass: • additional volume photon map • Second pass: • rendering using ray marching

  22. Volume Radiance Estimate • Estimate radiance using volume photon map

  23. Volume Radiance Estimate for Ray Marching • For each ray through the volume, we can get the radiance caused by volume scattering by marching along the ray and cumulating every in-scatteredradiance single scattering (direct):by ray tracing Multiple scattering (indirect): by volume radiance estimate

  24. Outline • Overview of Photon mapping for surfaces • Light transport in participating media • Extending Photon Mapping to Participating Media • Results

  25. Features of Volumetric Photon Mapping • Can model- • Homogeneous as well as non-homogeneous media. • Isotropic as well as anisotropic media. • Since decoupled from geometry (photons stored in kd-tree), so capable of handling complex scene.

  26. Some Results • Anisotropic and non-homogeneous medium

  27. Underwater Scene with Volume Caustics

  28. Pseudo code for volume photon mapping • http://www-graphics.stanford.edu/courses/cs348b-competition/cs348b-05/abandoned/index.html

  29. Thanks!

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