CS781 - Colour for Computer Graphics - Winter 2009

Lecture 4

Transport

Scattering

No Wavelength Dependence

Fog

Wavelength Dependence Mediated by Chromatic Aberration

Rainbow

Wavelength Dependence Mediated by Selective Absorption

Beer


Surface Reflectances

According to Jim Kajiya, Bidirectional Reflectance Distribution Function should tell the whole story. But where does it come from?

Maybe it could come from measurement

Maybe you could simulate the system

Maybe you could find a simple model

Smooth Surfaces

Surface reflectance

Body reflectance

Lambertian reflectance

Lambert 1728-1777

The Moon

Rough Surfaces

Surface Reflectance

Surface Gloss

Colour Mixing

Paint is the usual example, but there are other examples

  1. Fruit ripening
  2. Leaves turning colour in the fall
  3. Colour of human skin

Kubelka-Munk colour mixing model

  1. Infinitesimally thin layers, thickness proportional to the density of the pigment
  2. Use reflection/refraction plus Beer's law
  3. Solve in equilibrium at the boundaries between layers

Engineering model

Subjective Effects of Coloured Surfaces

Area effects

Precision of Colour Mixing


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