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Toward Real-Time Global Illumination

Toward Real-Time Global Illumination. Project Ideas. Distributed ray tracing Extension of the radiosity assignment Translucency (subsurface scattering). Global Illumination == Offline?. Ray Tracing and Radiosity are inherently slow. Speedup possible by:

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Toward Real-Time Global Illumination

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  1. Toward Real-Time Global Illumination

  2. Project Ideas • Distributed ray tracing • Extension of the radiosity assignment • Translucency (subsurface scattering)

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

  4. 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?

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

  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. Precomputed Light Transport

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

  9. 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

  10. 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)

  11. 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?

  12. 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)?

  13. 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

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

  15. Relighting as Matrix-Vector Multiply

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

  17. Ray-Tracing Matrix Columns

  18. Ray-Tracing Matrix Columns

  19. Light-Transport Matrix Rows

  20. Light-Transport Matrix Rows

  21. Light-Transport Matrix Rows

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

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

  24. Related Work SH PRT SH PRT Sloan et al. 2002 Kautz et al. 2002 Deformable BTF+PRT Bump mapping Gaussians Sloan et al. 2003 Sloan et al. 2005 Sloan et al. 2005 Green et al. 2006 Wavelet Double Wavelet Triple Wavelet Double Subsurface Ng et al. 2003 Ng et al. 2004 Wang et al. 2006 Wang et al. 2005

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