1 The Eye and Colour Vision By Michael Harwood updated Feb 2012

2 Contents Parts of the eye Requirements for vision Retina & rhodopsin Spectral response  colour vision Experiments to try Colour addition and “subtraction” Age effects, optical illusions,...

3 The Human Eye

4 Minimum Requirements for vision  very transparent cornea  very transparent lens  very transparent vitreous & aqueous humor  curved cornea  light sensitive cells we have two types with 4 colour sensitivities!  nerve cells & optic nerve

5 Minimum Requirements (continued...)  lens and humours must have different indices of refraction  eyelids  tearducts  lens focused to some useful distance  process of removing dead cells so that they don’t clog up the eye

6 Extra features ! Human eyes also have:  recessed eyes (protected by bones)  colour vision  vision over huge range of light intensities  moveable iris that controls amount of light  lens that can change focal length  eyebrows – keep water out of eye  eyelashes?

7 Extra features (continued...)  automatic feedback - focussing - iris - tracking - saccades and  -sac (to prevent fatigue)  binocular vision (two eyes on front of head)  excellent focus at fovea -- able to read text  colored iris – beauty (and prevention of scattering)  macula lutea – more UV protection on fovea

8 Retina

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10 Rods

11 Rhodopsin Rhodopsin is based on 11-cis-retinal + an opsin molecule. Retinal is based on Vitamin A. Maximum sensitivity at 498 nm

12 Rhodopsin

13 Rods vs Cones ConesRods Require a lot of light to work. Sensitive to low light; overpowered by normal light Detect colour (3 types)Only shades of gray Mostly near foveaMostly In periphery

14 Fovea vs Periphery

15 Spectral Sensitivity

16 Spectral Response

17 Primary Colours: R,G,B R+G = Y G+B = C B+R = M R+G+B = White

18 Colour "Subtraction" Secondary colours

19 CIE chromaticity diagram

20 Gamut