CMSC 635: Advanced Computer Graphics

Global Illumination

Spring 1999

David S. Ebert
Computer Science and Electrical Engineering Department
University of Maryland, Baltimore County

Global Illumination

Combining Ray Tracing and Radiosity -- Two pass method:

  • Pass1: Enhanced Radiosity - View Independent [Rushmerier 90]

    • handles:
      diffuse - diffuse

    • General Equation



      • diffuse transmission:
        where tex2html_wrap_inline52 is backward diffuse transmission.

      • * specular transmission: path j may specularly transmit
        light-window form factor

      • * specular-diffuse reflection: mirror form factor
        add terms to handle tex2html_wrap_inline56 seeing ``virtual'' tex2html_wrap_inline58 through mirror surface tex2html_wrap_inline60.

      * - The last two items are only for specular surfaces that can't see each other.

  • Pass2: ``Enhanced Ray-Tracing'' -- View Dependent

    • specular-specular -- normal ray tracing

    • diffuse-specular:

      • Integrate light arriving at reflection point by using a square pyramid in the direction of specular bump.

      • Divide into grid and do a z-buffer at low resolution to see what is visible -- use radiosity calculated intensities here.

      • can do recursively

    • only handles special cases of specular transmission and specular-diffuse reflection.

Rendering Equation [Kajiya 1986]



  • I(x,x') = transport intensity (from x' to x)

  • g(x,x') = visibility between x and x'

  • tex2html_wrap_inline76 = transfer emittance from x' to x.
  • tex2html_wrap_inline82 = scattering or bidirectional reflectivity -- intensity of light at x' from x''scattered in direction x.

  • s means all points on all surfaces in the scene.


    transport from x' to x =
sum of light emitted from x' in direction of x
plus the total light scattered from x' to x from all other surfaces.

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Last modified: Wed Mar 3 15:16:44 EST 1999