# cs781 - Colour for Computer Graphics - Winter 2012

# Course Notes

# Lecture 15 - Linear Models of Reflectance

## And Now from our Sponsor

- Projects
- Last three lectures
- Talk on flicker hallucinations

Dr. Bard Ermentrout (Computational Biology, University of Pittsburgh,)

Flicker Hallucinations: Faraday waves in the brain

3.30 p.m., Tuesday, 6 March

MC 5158.

# Linear Models of Colour

Where did it come from

- remote sensing
- paint analysis

## Principal Components Analysis

Given a very large sample of data, how can you summarise it?

- e.g. spectral power distributions from many sources of light
- PQR decomposition

#### Weaknesses

- The usual least squares problems
- and there is no well-accepted way of doing other metrics
- Why? Because of the other problems

- Sample dependence
- You have to redo it for each new sample

- There is usually not a well-defined break point

#### Possible Remedies

- We know the dimension

## PCA of Coloured Surfaces

## PCA of Coloured Light

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