NATS 1870 Study Guide - Final Guide: Color Vision, Contrast Effect, Anthocyanin

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SC NATS 1870 (lecture) Monday,
October 19, 2009
1. Give two examples of how the development of a new pigment has had an impact on
painting and painting style.
Ultramarine used for religious figures hard to make, expensive
Household & car paint arsenic based green paints & less choice of paint depended on
mass market
2. Describe the chemical process responsible for leaves turning:
a) green to yellow; b) green to red
Keratin green to yellow
Anthocyanin green to red
Not all leaves go red, needs high sugars anythocyanin
Usually outside facing south turns red first
Red outside of tree 1st, green more on inside
Color Perception + Mixtures Additively
Background color affects way color perceived
Cones affect/help perceive color, doesn’t see fixed color
Process called simultaneous, adaptive process
Color perception
Is an active process eye + brain are continually comparing objects, surrounding,
illumination conditions
Give rise to certain “adaptive processes” like simultaneous contrast
A color will appear different depending on its surroundings
Visual sense responds to visible light
Color vision: process of decoding
1) wavelength (λ)
2) intensity (I)
Response to visible light is based on chemical process in cells cones & rods
Photons of visible light are absorbed by specific molecules photo pigment molecules
very large molecules that resemble caratine, Vitamin A
Millions of them are stacked in each rod & cone
Large cells
Responsible for black & white vision
Located: tends to be concentrated towards edge of retina
Less precise vision
About 100 million rods
One type
Contains “rhodopin”
Function in low levels of light
The Color Theory
Postulated in 1801 by Thomas Young
3 types of “resonators” in eye, that responded to red, green, blue light
Small cells
Responsible for color vision
located: tend to be centrally concentrated
at back of eye in foeva
give sharp detailed vision
approximately 6 million cones
3 types: red, green, blue
R sensitive cones
G sensitive cones
B sensitive cones
Each contain slightly different photo
pigment molecules called “opsins”
Need bright light sources to trigger cones
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