cs781 - Colour for Computer Graphics - Winter 2012

Course Notes

Lecture 4 - Photoreception

And Now from our Sponsor

  1. Any new students?
  2. Windows in the atmosphere
  3. Overview of colour matching

Interaction of Light and Matter

Visual optics


Bacterial purple: ion pump

Rods and cones: G-coupled

Ganglion and other cells:



Ganglion Cells and Others

Quality of Photodetection

Absolute Thresholds

Dynamic Range

  1. Of individual photoreceptors: controversial, but the biggest estimates are below 1000.
  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
    Dark adapted vision

    Rod threshold: -6, 20 photons per second

    -2 to -1 Night with moon Rods & cones

    Cone threshold: -2, 20,000 photons per second

    -1 to +2 Between night & day
    Colour vision
    Snow under full moon: +0.3
    Rods & cones

    Rod saturation: +2

    +2 to +4 Dawn, overcast
    Cloudy sky: +3.3
    Full moon: +3.5

    Clear sky: +4

    Cones Photoopic
    +4 to +6 Bright sun

    Solar disk at horizon: +5.7

    Cones, bleaching Photopic
    +6 to +9 Staring at sun: +9
    Atomic bomb: +8.3
    Cones, damaged

    Atomic bomb is worse than sun

    Don't look!

The above table

For comparison

Typical displays

The Principle on which the Computer Graphics Use of Colour is Based.

`If the photoreceptors provide the same signal to the brain, the perceptual systems of the brain will provide the same visual experience.'

This principle is made operational by the principle of univariance: `the signal provided by any photoreceptor depends only on the number of photons absorbed.'

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