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Problem 4 colour (Perceived colours (white is equally distributed across…
Problem 4 colour
Perceived colours
white is equally distributed across spectrum
all frequencies appear white
extraspectral (everything but red, yellow, green, blue)
saturation is changed by intensity (pale ---> vivid)
red, yellow, green, blue
add white ---> less saturated (e.g. blue + white = sky blue)
Trichromatic theory
amount of stimulation influences colour
each wavelength has a certain activity in each receptor
3 photo receptors
colour matching experiment
normal people need only 3 wavelengths
colour diffeciencies need 2 wavelenghts
from 3 colours people can create all colours in combination
Helmholtz + Young
physiology
3 cones
S-cones = short wavelengths
M-cones = medium wavelengths
L-cones = long wave lengths
colours & wavelength
colour is not a physical property
Chromatic
selective reflection (reflected light)
other colours
selective transmission
some wavelengths pass through (transparent objects)
chromatic colours are created by selective transmission
wavelengths do not contain colour
Achromatic
white, black
Opponent-process theory
3 mechanisms responding to wavelengths
black - white
positive ---> white
negative ---> absence
red - green
positive ---> red
negative ---> green
blue - yellow
positive ---> yellow
negative ---> blue
evidence!
opposing neurons
ganglion cells
L + M - s
L -M
After image
experiment
3) new image
4) changed colour from staring
2) stare at colour
simultaneous colour contrast
1) look at different patches of colour
vision cased by opposing responses to colours
Colour dificiencies
Monochromatism
no functioning cones
only shades of gray
only need 1 wavelength
sensitive to bright lights (red vision)
colour blind
usually hereditary
Dichromatis
Deuteranopia
missing M-cone
can only see blue & yellow
protanopia
missing L-cone
cannot see red
Tritanopia
see blue & red
most rare
Anamalous trichromat
protanopia + deuteranopia + tritanopia
cannot discriminate between wavelengths close together
Ishihara plats
red - green colour dificiency
mixing
light
additive colour mixture
all combined ---> white
super imposed light
combining wavelengths
paints
subtractive colour mixture
physiology
trichromatic
explains from external ---> retina
opponent- process
integrates inhibitory & excitatory cells
Functions of colour vision
helps in caragorizing & organizing