Colour Flashcards
(27 cards)
Give 2 evolutionary purposes of colour vision.
For detecting food and predators and finding the ‘best’ mate.
What is visible light?
A narrow band of EM radiation in the wavelength range 400 - 700 manometers.
What are the 3 physical dimensions of colour?
Hue, saturation and value/brightness.
Why do lights look a certain colour?
Because, among different wavelengths, the peak light emitted is that colour.
Why do objects look a certain colour?
The object absorbs short wavelength light and reflects long wavelength light.
What is reflected light?
Light that impinges on the eye from an object that does not emit light.
Why is colour mixing of paints subtractive?
When combined, only wavelengths reflected by both paints reach the eye.
Why is colour mixing of lights additive?
When combined, light from a wider range of wavelengths reaches the eye.
What causes coloured after-effects?
Adaptation of the mechanism means the ratio appears as if the opposing mechanism is more active.
What evidence supports Opponent Theory?
Coloured after-effects.
What evidence supports Trichromatic Theory?
Colour mixing, three types of cone receptors and colour blindness.
What is colour matching?
A pure light can be matched to a combination of a triplet of other lights.
What are metamers?
Same perceived colour, different physical spectrum.
How does human visual sensitivity to the range of visible wavelengths support Trichromatic Theory?
Humans have peak sensitivity in 3 places, which are consistent with cone cells in the retina.
How do 3 receptors represent all the colours that we see?
We use the ratio of responses.
Which cone type is missing in protanope colour blindness?
Long.
Which cone type is missing in deuteranope colour blindness?
Medium.
Which cone type is missing in tritanope colour blindness?
Short.
How does Dual Process Theory reconcile the other theories?
It describes how the 3 receptors work as several opponent processing systems.
When are rod cells useful?
In low illumination.
What structure do opponent process cells in LGN have?
Centre-surround.
What structure do opponent process cells in V1 have?
Double opponent cells (side by side).
Why is measuring colour in the context of other colours in a scene useful?
Helps us perceive colour and brightness as we move around.
What is luminance?
Illumination X reflectance.
