CS781 - Colour for Computer Graphics - Winter 2009

Lecture 16

Colour Spaces

Remember when you were in high school

The four categories below represent increasingly objective/mathematical ways of describing colour

Based on Substances

Pigments

Stone Age

Iron oxide

Egyptians

Greeks

Vermillion

Reluctance to mix pigments

Renaissance

Ultramarine

Based on Samples

Munsell

OSA

Artist's Colour Spaces

Device Dependent

Additive Primaries

RGB

HSV, HLS, HSB, HVC, etc.

RGYB

YIQ

Subtractive Primaries

Device Independent

Based on instrumental measurement

Tristimulus Values

Chromaticity Coordinates

Colour Difference

The colour spaces above give us

  1. increasingly standardized colour identity
  2. correct colour topology

They do not give us a measure of colour difference!

Lot's of ways to do colour difference experiments

Question 1

Question 2.

Two answers were provided by the CIE in 1978.

  1. The first answer was 3, which is incorrect; the second answer was twins, two uniform colour spaces.
  2. Luv
  3. Lab

Why are there two?

What does this mean about colour difference?

Comparing Images

Here's three ways that it is done

  1. Sum ( (R - R")^2 + (G-G')^2 + (B - B')^2 ) ^(1/2) over pixels
  2. Sum ( (X - X")^2 + (Y-Y')^2 + (Z - Z')^2 ) ^(1/2) over pixels
  3. Sum ( (L - L")^2 + (u-u')^2 + (v - v')^2 ) ^(1/2) over pixels

Why are neither of these satisfactory?

Suggestions for improvement.


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