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Radiosity

Radiosity is a rendering technique that models diffuse inter-reflection, color bleeding, and soft shadows by accounting for indirect illumination. It is a global illumination method that assigns brightness to every surface, resulting in view-independent lighting.

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Radiosity

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  1. Radiosity Dr. Scott Schaefer

  2. Radiosity

  3. Radiosity • Physically based model for light interaction • View independent lighting • Accounts for indirect illumination • Color bleeding • Soft shadows

  4. The Rendering Equation

  5. The Rendering Equation Outgoing radiance from surface at p in the direction v

  6. The Rendering Equation Emitted radiance from surface at p in the direction v

  7. The Rendering Equation BRDF of surface at p

  8. The Rendering Equation Ray cast from p in the direction of l

  9. The Rendering Equation Output radiance of intersected surface in the direction of -l

  10. The Rendering Equation Angle between l and n

  11. The Rendering Equation Integral about hemisphere centered at p

  12. BRDF’s Bidirectional Reflectance Distribution Function • Determines amount of incoming light from direction l reflected from surface in the direction of v Image taken from “A Data-Driven Reflectance Model”

  13. Discretizing the Rendering Equation • Assume perfectly diffuse surfaces • Discretize space into patches • Color is constant per patch Image taken from “Radiosity on Graphics Hardware”

  14. Discretizing the Rendering Equation

  15. Discretizing the Rendering Equation

  16. Geometric Computation of Form Factors

  17. Geometric Computation of Form Factors

  18. Geometric Computation of Form Factors

  19. Geometric Computation of Form Factors

  20. Geometric Computation of Form Factors

  21. Geometric Computation of Form Factors

  22. Geometric Computation of Form Factors Project patches onto hemisphere

  23. Geometric Computation of Form Factors Project spherical patches onto tangent plane

  24. Geometric Computation of Form Factors Divide by area of disc in tangent plane ( for surfaces)

  25. Geometric Computation of Form Factors Divide by area of disc in tangent plane ( for surfaces) Fi,j= form factor

  26. Matrix Computation of Radiosity

  27. Matrix Computation of Radiosity

  28. Matrix Computation of Radiosity Jacobi iteration

  29. Matrix Computation of Radiosity

  30. Matrix Computation of Radiosity

  31. Matrix Computation of Radiosity

  32. Matrix Computation of Radiosity

  33. Matrix Computation of Radiosity

  34. Radiosity Examples Image taken from http://www.9jcg.com/tutorials/jason_jacobs/radiosity_01.jpg

  35. Radiosity Examples

  36. Radiosity Examples Image taken from www.cs.dartmouth.edu/~spl/Academic/ComputerGraphics/Fall2004/radiosityExample.jpg

  37. Advantages of Radiosity • Global illumination method: modeling diffuse inter-reflection • Color bleeding: a red wall next to a white one casts a reddish glow on the white wall • Soft shadows: an area light source casts a soft shadow from a polygon • No ambient hack • View independent: assigns a brightness to every surface

  38. Disadvantages of Radiosity • Radiation is uniform in all directions • Radiosity is piecewise constant • No surface is transparent or translucent • Must determine how to subdivide shapes into small enough patches

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