CS781 - Colour for Computer Graphics - Winter 2009

Lecture 8

Visual Response to Light

Colour Matching Functions

Metamerism

Light Metamerism

Many to one transformation

Evolution says:

Illuminant Metamerism

Hold the surface constant

Surface Matemerism

Hold the illuminant constant


Geometric Representations of Colour

Special Properties of the Spectral Colours

Colours in the rainbow/spectrum = Colours of monochromatic lights

Mix a spectral colour and white

Mix the same spectral colour with any other colour

Remove a little of the spectral colour

Choose another spectral colour

Convex Hull of the Spectral Colours

This is the set of physically realisable colours


Chromaticity Coordinates

The two meanings of `colour' when we say, `the same colour.'

  1. Unique hue, saturation and brightness
  2. Unique hue and saturation

Remember (?) projective geometry

Consider the projection

The resulting planar representation of colour is called `chromaticity coordinates'

It is pretty well impossible to make a true colour picture of the chromaticity diagram

Concepts from chromaticity coordinates

The white point

The purple line

Dominant hue

Excitation purity

Colour Temperature


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