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Interreflections and Radiosity : The Forward Problem Lecture #11

Interreflections and Radiosity : The Forward Problem Lecture #11. Thanks to Kavita Bala, Pat Hanrahan, Doug James, Ledah Casburn. Cornell Box. blue hue. red hue. Phong Shading. Plastic looking scene. no object interactions. no shadows. Ray Tracing. Scene doesn’t look realistic enough.

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Interreflections and Radiosity : The Forward Problem Lecture #11

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  1. Interreflections and Radiosity : The Forward Problem Lecture #11 Thanks to Kavita Bala, Pat Hanrahan, Doug James, Ledah Casburn

  2. Cornell Box blue hue red hue

  3. Phong Shading Plastic looking scene • no object interactions • no shadows

  4. Ray Tracing Scene doesn’t look realistic enough. • where is the corner of room? • is window flush with wall? • is the carpet and wood supposed to be this dark?

  5. Radiosity – today’s topic Indirect lighting affects realism. • room has a corner • window has depth • carpet and wood on table • is lighter • walls look more pink

  6. The Rendering Equation – Graph Style p’’ source viewer p’ p Reflectance from Surfaces Emission (light source) Visibility (shadows)

  7. Diffuse Interreflections - Radiosity • Consider lambertian surfaces and sources. • Radiance independent of viewing direction. • Consider total power leaving per unit area of a surface. • Can simulate soft shadows and color bleeding • from diffuse surfaces. • Used abundantly in heat transfer literature

  8. Irradiance, Radiosity • Irradiance E is the power received per unit surface area • Units: W/m2 • Radiosity • Power per unit area leaving the surface (like irradiance)

  9. Planar piecewise constancy assumption • Subdivide scene into • small “uniform” polygons

  10. Power Equation • Power from each polygon: • Linear System of Equations:

  11. Form Factors Invariant

  12. Form Factor Computation • Schroeder and Hanrahan derived an analytic expression • for polygonal surfaces. • In general, computing double integral is hard. • Use Monte Carlo Integration.

  13. Form Factor Computation

  14. Form Factor Computation

  15. Linear System of Radiosity Equations Known Known Unknown • Matrix Inversion to Solve for Radiosities.

  16. Doug James

  17. Wireframe

  18. Classical • Approach • No • Interpolation

  19. Wireframe

  20. Classical • Approach • Low Res

  21. Classical • Approach • High Res • More accurate

  22. Classical • Approach • High Res • Interpolated

  23. Sample Scenes

  24. Sample Scenes

  25. Sample Scenes

  26. Sample Scenes

  27. Sample Scenes

  28. Summary

  29. Doug James

  30. Two Pass Solution • First Pass: Diffuse Interreflections • View independent, global diffuse illumination • computed with radiosity. • Second Pass: Specular Interreflections • View dependent, global specular illumination • computed with ray-tracing. • Combine strengths of radiosity and ray-tracing.

  31. Interreflections : The Inverse Problem Lecture #12

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