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Toward Real-Time Global Illumination

Toward Real-Time Global Illumination. Global Illumination == Offline?. Ray Tracing and Radiosity are inherently slow. Speedup possible by: Brute-force: more hardware, multicore…etc. Approximate results. Under Simplified Assumption. Can it become faster if: …the view is fixed?

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Toward Real-Time Global Illumination

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  1. Toward Real-Time Global Illumination

  2. Global Illumination == Offline? • Ray Tracing and Radiosity are inherently slow. • Speedup possible by: • Brute-force: more hardware, multicore…etc. • Approximate results

  3. Under Simplified Assumption • Can it become faster if: • …the view is fixed? • …the scene is static? • …the lights are simple? • …if indirect lighting is limited?

  4. Lighting Design • Assuming: • Static scene • Fixed (or limited) view • Example: • Lpics: a hybrid hardware accelerated relighting engine for computer cinematography, SIGGRAPH 2005

  5. Lpics Source: http://www.vidimce.org/publications/lpics/pdf/lpics-final-compressed.pdf

  6. Instant Radiosity (and the Problem of Many Lights?) • What if we place many virtual light sources to represent indirect lighting? • How do we handle a very large number of light sources? • Lightcuts: A Scalable Approach to Illumination, SIGGRAPH 2005

  7. Reflective Shadow Maps • Dachsbacher and Stamminger. 2005 symposium on Interactive 3D graphics and games (I3D '05). Source: http://dl.acm.org/citation.cfm?doid=1053427.1053460

  8. Precomputed Light Transport

  9. Indirect Lighting • Many indirect lighting effects are subtle, yet crucial for visual realism. Examples are: • Soft shadow • Ambient occlusion

  10. Ambient Occlusion • Ambient light is a very crude approximation to indirect reflections of surrounding objects. • What if a point can’t see much of its surrounding? From: Janne Kontkanen & Samuli Laine ACM I3D 2005

  11. Soft Shadow from Environment Lighting Sen, Cammarano, Hanrahan, 2003 Sloan, Kautz, Snyder 2002 Shadows from smooth lighting (precomputed radiance transfer) Shadows from point-lights (shadow maps, volumes)

  12. Beyond Monte Carlo Path Tracing? • Are global illumination solvers always time consuming? • What if the scene and the lights are static ?  Radiosity (view can changes!) • What if only the scene is static?

  13. Light Stage • Take photos under single point light at various positions. • Trivial questions: how to produce new images at: • Two point lights? • Area light? • Environment light (captured by light probe)?

  14. Precomputed Light Transport • Three important papers to start with: • "Precomputed Radiance Transfer for Real-Time Rendering in Dynamic, Low-Frequency Lighting Environments" Sloan et al., SIGGRAPH 2002 • "All-Frequency Shadows Using Non-linear Wavelet Lighting Approximation" Ng et al., SIGGRAPH 2003. • "Triple Product Wavelet Integrals for All-Frequency Relighting" Ng et al.  SIGGRAPH 2004

  15. The following 8 slides are from Ren Ng’s SIGGRAPH 2003 presentation

  16. Relighting as Matrix-Vector Multiply

  17. Relighting as Matrix-Vector Multiply • Output Image(Pixel Vector) • Input Lighting(Cubemap Vector) • TransportMatrix

  18. Ray-Tracing Matrix Columns

  19. Ray-Tracing Matrix Columns

  20. Light-Transport Matrix Rows

  21. Light-Transport Matrix Rows

  22. Light-Transport Matrix Rows

  23. Rasterizing Matrix Rows Pre-computing rows • Rasterize visibility hemicubes with graphics hardware • Read back pixels and weight by reflection function

  24. Low-Frequency vs. All-Frequency Teapot in Grace Cathedral

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