cs781 - Colour for Computer Graphics - Winter 2012

Course Notes

Lecture 14 - Reflectance

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  1. Projects

Surface Reflectances

Smooth Surfaces

Surface reflectance

Rough Surfaces

Random roughness

Surface is well-modelled as a collection of small flat surfaces oriented in random directions

Structured roughness

Some of the most interesting BRDF effects are the result of structured roughness

Between Rough and Smooth

Surface Gloss

Body Reflectance

Multiple interaction with pigment

  1. Encounters with two identical pigment particles.
  2. Encounters with two different pigment particles.

Lambertian reflectance

Lambert 1728-1777

Consider a small circular hole in the surface and ask how much light comes through it in different directions

The luminance of light in any direction is constant.

When the volume immediately below the surface has spatial structure, the direction of light re-emitted through the surface is not necessarily isotropic.

The Moon

Colour Mixing in Body Reflectance

Paint is the usual example, but there are others

  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

Recall difference between

computer-animated movies -- let the artist play with coefficients

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