CS781 - Colour for Computer Graphics - Winter 2009
Lecture 8
Visual Response to Light
Colour matching functions depends on something done by humans,
- namely, colour matching
- How do they do it?
Light enters eye
1. The Eye
Cornea
Iris
Lens
Acqueous & Vitreous Humours
Sclera
Macular Pigment
Optical Quality
Aging
Colour Quality
Aging
2. The Retina
Overall Layout
Blood vessels
Fovea
- all cones
- no blood vessels
- foveal pit
Periphery
- mixture of rods and cones
Generic Photoreception
Bacterial purple: ion pump
Rods and cones: G-coupled
Ganglion cells:
- genetically like bacterial purple
- but G-coupled
Rods
- 100 million in the human retina
- big, fast
Cones
- 10 million in the mouse retina
- small, near the diffraction limit
- slow
Ganglion Cells and Others
- only 700 in the mouse retina
Quality of Photodetection
Absolute Thresholds
- rods
- 6 photons at the cornea
- 2 photons absorbed
- a candle at 3-10 Km
- cones
- 1000 times as high as rods
- ganglion cells
- 100,000 times as high as rods
- 100 times as high as cones
Dynamic Range
- Of individual photoreceptors
- 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
- CRT monitors: +1 to +3
- LCD monitors: +1.5 to +3.5
- LCD projectors: +1 to +3
Or another set of categories (minima)
- reading +2.5
- industrial work +3.5
- surgery +4.5
3. Neural Processing
Amacrine Cells
Bipolar Cells
Ganglion Cells
Inter-cell Communication
Synapses
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