1 - PRIMARIES IN OPPONENT COLOUR THEORY Flashcards
blue + yellow = white light
- the white light has no traces of blue or yellow in it
- same as when red and green make yellow
which colours have pure shades?
- yellow
- blue
- red
- green
- psychological primaries
- no trace of other colours
- same with white and grey but they’re said to lack colour (achromatic)
mixtures of colour examples on pg 2 of week 3
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pairs in opponent colour theory
red-green
blue-yellow
how the pairs work
- the colours in the pairs are opposites
- adding them together = removes the original colours
- results in white or yellow
- with no trace of the other colours
adding more colour of a pair
- as more of one colour gets added (intensity increases), the paler/yellower the other colour becomes until there’s none left and it looks white or yellow
- at no point does the mixture look like the yellow you’re adding
- progressively weakens the colour until there is none left (but still an additive mixture as adding more light)(gets brighter and brighter)
- saturation = strong colour
why is it called opponent colours?
- because adding the opposing colour results in the removal of the other
ewald herings thoughts
- something significant about the fact that there is no yellowish blue or reddish green
- they appear to be mutually exclusive
- OPPONENT COLOURS THEORY
primaries in opponent colour theory
- unique
- pure shades
- four
but in trichromacy can be three colours, and not exclusive to a certain set
- not unique
opponent mechanisms 1
the human visual system which contains two mechanisms that put the colours in each pair in opposition
- blue/yellow
- red/green
david hubels view of opponent mechanisms
- red and green can make white (not yellow)
- but the red needs to be slightly bluish (magenta)
- and the green needs to be slightly bluish (kinda cyan)
- these aren’t ‘pure’ colours like hering said
- they are mixtures
opponent mechanisms 2
- mechanism consists of a detector that responds to red light and one which responds to green light
- also a unit that combines the signals transmitted by these two detectors
- same for blue and yellow
- combination unit is excited by signals transmitted by one detector and inhibited by signals from the other
- ensures that both colours can’t be seen in a mixture
- eg no bluish yellows or reddish greens
- combination unit can signal which colour is dominant (provided it has a resting level of activity that it produces when there is no stimulation)
= signals no colour present - cancel each other out if equal signal from each detector
- the greater signal is evoked - so only one sensation at a time
example of a blue yellow opponent mechanism
- blue excites
- yellow inhibits
only blue light shone into eye:
- blue light detector stimulated
- yellow is not
- activity of the combination unit above the resting level
- signals blue is present so only blue is seen
only yellow light shone into eye:
- activity in combination unit decreases below resting level
- signals yellow light is present
- yellow is seen
hering said there is a third opponent mechanism for achromatic colours but that’s all james says
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herings theory was largely ignored for several decades (until the 1950s)
- because they believed trichromatic theory and both aren’t compatible
- gained recognition because it could overcome certain difficulties from trichromacy theory
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