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The Eye and Colour Vision

By Michael Harwood

updated Feb 2012

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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, ...

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The Human Eye

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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

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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

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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?

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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

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Retina

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Retina

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Rods

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Rhodopsin

• Rhodopsin is based on 11-cis-retinal + an opsin molecule.

• Retinal is based on Vitamin A.

• Maximum sensitivity at 498 nm

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Rhodopsin

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Rods vs Cones

Cones Rods

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 fovea Mostly In periphery

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Fovea vs Periphery

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Spectral Sensitivity

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Spectral Response

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Primary Colours: R,G,B

R+G = Y

G+B = C

B+R = M

R+G+B = White

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Colour "Subtraction"

Secondary colours

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CIE chromaticity diagram

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Gamut