CS781 - Colour for Computer Graphics - Winter 2009

Lecture 9

Visual Response to Light

Colour matching functions depends on something done by humans,

1. The Eye

Cornea, Iris, Lens, Acqueous & Vitreous Humours: Optical Quality

  1. Aging
  2. Chromatic abberation

2. The Retina

Rods, Cones, Ganglion Cells and Others

Quality of Photodetection

Absolute Thresholds

Relative Thresholds

Dynamic Range

  1. Of individual photoreceptors
  2. Of the entire system. Numbers are log_10 (lux = lumens /m^2)
    Light level Natural conditions Photodetectors Greek name
    -5 to -2 Moonless night Rods Scotopic
    -2 to -1 Night with moon Rods & cones Mesopic
    -1 to +2 Between night & day Cones Photopic
    +2 to +4 Dawn, overcast Cones Photoopic
    +4 to +6 Sunny Cones, bleaching Photopic
    For comparison Or another set of categories (minima)
  3. Sources of the `mismatch': factor of 100,000,000 [8] to be found
    Mechanism Factor log_10
    Pupil size 30 1.5
    Gain in photoreceptors

    100(?)

    2

    Pigment bleaching

    100(?)

    2

    Synaptic gain (horizontal cells) 100(?)

    2

3. Neural Processing

Amacrine Cells, Bipolar Cells, Ganglion Cells

  1. Synapses
  2. Spatial opponent organization
  3. Colour opponent organization

4. Opponent colours theory

Psychophysical phenomena

  1. Reddish-green and yellowish-blue
  2. Unique hues
  3. Flicker photometry
  4. Minimally distinct border
  5. Colour naming
  6. Unusual properties of yellow-blue axis

Neural Theories

Other interesting observations

  1. Basic colours
  2. Cardinal colours

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