CS488 - Introduction to Computer Graphics - Lecture 27

Global Illumination


Calculating illumination

The Light Field

Plenoptic Function

Think about what the viewer can do.

  1. The seriously handicapped viewer can

    Ray tracing is perfect.

  2. The mildly handicapped viewer can

    Ray trace onto a sphere surrounding the viewer and reproject from the sphere to a view plane whenever the direction of gaze changes.

  3. The unhandicapped viewer can

    Ray trace onto a sphere at each accessible point.

The third is the light field, also called the plenoptic function, and it has to be recalculated every time something in the scene moves.

Filling Space with Light

Let's turn our attention away from the surfaces of objects and onto the volume between objects

At every point in this volume there is a light density

This quantity LF(P, <z>, \lambda ) is the light field. If we knew it we could

The evaluation is, in fact, just a projective transformation of the light field.

How do we get the light field?

  1. by measurement
  2. by calculation

How is the light field used in 2009?

But tomorrow!!

`Backdrop' Applications

Imagine making a game or a movie

An easy backdrop

Other Phenomena at Surfaces

Fresnel Reflection (See also.)

How does reflection actually work?

The key concept is the index of refraction

Reflected and refracted rays

Subsurface Scattering

Think about the Lambertian surface

A general formulation

Bidirectional Reflectance Function

BRDF as an example of partitioned rendering


  1. Surface of CD
  2. Some fabrics
  3. Desert sand
  4. Recently cut grass

Where do BRDFs come from?

  1. Extensive measurement
  2. Micromodelling


Examples of Micromodelling

Human skin

Obviously the second strategy is better,

Note two different definitions of `agrees with reality'.

Newly cut grass

Surface of CD

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