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A Practical Analytic Single Scattering Model for Real Time Rendering

A Practical Analytic Single Scattering Model for Real Time Rendering. Bo Sun Columbia University Ravi Ramamoorthi Columbia University Srinivasa Narasimhan Carnegie Mellon University Shree Nayar Columbia University.

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A Practical Analytic Single Scattering Model for Real Time Rendering

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  1. A Practical Analytic Single Scattering Model for Real Time Rendering Bo Sun Columbia University Ravi Ramamoorthi Columbia University Srinivasa Narasimhan Carnegie Mellon University Shree Nayar Columbia University Sponsors: ONR, NSF

  2. Scattering in Participating Media

  3. Scattering in Participating Media Loss of contrast

  4. Scattering in Participating Media Dimming and blur Loss of contrast

  5. Scattering in Participating Media Glows Dimming and blur Lost of contrast

  6. Direct Transmission Light Transport in Clear Day Point Source Viewer Surface Point

  7. Scattered (glows) Direct Transmission Light Transport in Scattering Media Point Source Viewer Surface Point Clear Day Foggy Day Clear Day Foggy Day

  8. Complexity of Rendering Scattering Media Objects Virtual Viewpoint Virtual Screen

  9. Complexity of Rendering Scattering Media Objects Virtual Viewpoint Virtual Screen

  10. Complexity of Rendering Scattering Media Objects Virtual Viewpoint Virtual Screen

  11. Complexity of Rendering Scattering Media Objects Virtual Viewpoint Virtual Screen 640 x 480 (image) x 4 (lights) x [ 50 (steps) + 100 ( directions ) x 50 (steps)] x 30 (intersect) = ? 1.9 Trillion Calculations 3.0 GHz CPU?

  12. Previous Work • Monte Carlo Ray Tracing Methods [Kajiya and Herzen 1984], [Max et al. 1994]… - Impressive effects, but slow Accuracy Speed

  13. Previous Work • Monte Carlo Ray Tracing Methods [Kajiya and Herzen 1984], [Max et al. 1994]… - Impressive effects, but slow • Hardware-accelerated Numerical Methods [ Dobashi et al. 2002 ], [ Riley et al. 2004 ] …. - Specialized for skies or clouds and Expensive precomputation • - No effects of scattering on surface radiance Accuracy Speed

  14. Previous Work • Monte Carlo Ray Tracing Methods [Kajiya and Herzen 1984], [Max et al. 1994]… - Impressive effects, but slow • Hardware-accelerated Numerical Methods [ Dobashi et al. 2002 ], [ Riley et al. 2004 ] …. - Specialized for skies or clouds and Expensive precomputation • - No effects of scattering on surface radiance • Glows around point sources [ Max et al. 1986 ], [ Biri et al. 2004 ]… • - Approximations which are not feasible in many cases • - Not extendable to surface radiance and complex lighting Accuracy Speed

  15. Our Technical Contributions • Explicit compact Airlight formula • Explicit Surface Radiance formula - Accurate - Simple fragment shader - Fully interactive Assumptions: • Isotropic point light sources • Homogenous media • Single scattering • No volumetric shadows

  16. The Airlight Integral Point Source, s : scattering coefficient of the medium Surface Point, p Viewer, v

  17. The Airlight Integral Point Source, s : scattering coefficient of the medium Surface Point, p Viewer, v

  18. The Airlight Integral Point Source, s : scattering coefficient of the medium Surface Point, p Viewer, v

  19. The Airlight Integral Point Source, s : scattering coefficient of the medium Surface Point, p Viewer, v

  20. The Airlight Integral Point Source, s : scattering coefficient of the medium Surface Point, p Viewer, v

  21. The Airlight Integral Point Source, s : scattering coefficient of the medium Surface Point, p Viewer, v

  22. The Airlight Integral Point Source, s : scattering coefficient of the medium Surface Point, p Viewer, v

  23. The Airlight Integral 4D: We want: - Low dimensional tabulation and cheap evaluation - Interactively change physical parameters

  24. - combine and - combine and The Airlight Model-Solution 4D:

  25. - combine and - combine and The Airlight Model-Solution 4D:

  26. - combine and - combine and The Airlight Model-Solution 4D: 2D

  27. Special Function F • Well behaved and purely numerical 2D function. • Independent of the scene. • Evaluate once for all and stored as a 2D texture.

  28. Our Compact Airlight Formula 2D: • Compact 2D representation. • Real time cheap evaluation. • Arbitrarily change physical parameters. • Fully interactive

  29. Our Compact Airlight Formula 2D: • Compact 2D representation. • Real time cheap evaluation. • Arbitrarily change physical parameters. • Fully interactive

  30. Our Compact Airlight Formula 2D: • Compact 2D representation. • Real time cheap evaluation. • Arbitrarily change physical parameters. • Fully interactive

  31. Our Compact Airlight Formula 2D: • Compact 2D representation. • Real time cheap evaluation. • Arbitrarily change physical parameters. • Fully interactive

  32. Comparison with Monte Carlo simulation Low RMS error shows our model is physically accurate

  33. Video: Glows Video clip 1

  34. BRDF Light Transport Revisited Point Source, s Viewer, v Surface Point, p

  35. Lambertian and Phong Spheres Clear Day Lambertian Phong=10 Phong=20 Foggy Day

  36. : , 2D 1D function on : Lambertian, Phong 2D: The Surface Radiance Model Point Source, s BRDF Viewer, v Surface Point, p

  37. Video: Diffuse and Glossy Shading Video clip 2

  38. 2 Lookups and 2 Lookups The Complete Model Surface Radiance Model Airlight Model

  39. 2 Lookups and 2 Lookups 15 Million VS 1.9 Trillion Image size Lights Terms to approximate the phase function = 5 Million = 10 Million The Complete Model Surface Radiance Model Airlight Model Texture lookups Analytic expression

  40. Snap Shot of Shader Code float AirLight( ) { float u = A1(beta, Dsv, gammasv); float v1 = 0.25*PI+0.5*atan((DvpDsv*cos(gammasv))/(Dsv*sin(gammasv))); float v2 = 0.5*gammasv; float4 f_1=texRECT(F, v1, u); float4 f_2=texRECT(F, v2, u); return A0(lightIntensity, beta, Dsv, gammasv)*(f_1.x-f_2.x); } float SurfaceRadiance( ) { float4 G = texRECT(G_20, Tsp, thetas); return Ks*Io*beta/(2*Dsp*PI)*G; }

  41. Video: Complex Geometry Video clip 3

  42. For Live Demo, please visit sketch at 10:30am, Patree Hall A.

  43. BRDF Complex Lighting and Materials • Rendering time is linear in the number of lights. Viewer, v Surface Point, p

  44. Intensity Angles Point Spread Function • Equidistant point sources • Scattering is essentially Point Spread Function (PSF). [Narasimhan and Nayar 2003], [Premoze et al. 2004]… Input Output PSF

  45. Intensity Angles Complex Materials Effective BRDF with Scattering BRDF PSF Clear Day Foggy Day

  46. Intensity Angles Environment Maps Lighting Foggy Lighting PSF Clear Day Foggy Day

  47. PSF for Complex Lighting and Material Video clip 4 and 5

  48. Visual Effects and Performance Comparisons

  49. Visual Effects and Performance Comparisons

  50. Visual Effects and Performance Comparisons

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