Colour perception Flashcards
Function of colour percpetion
- Helps humans search for things
- Make judgements
- Spot and identify poison
- Attract a mate
Physics of colour
- Visible light is a electromagnetic radiation with wavelengths from 400-700 nm
- White light is a mixture of colours
Why do objects appear opaque or transparent
- opaqueness due to light not being able to pass through (red colour = blue light absorbed)
- transparency is determined by the colour it transmits
mixing light
Blue objects absorbs red light but reflects blue and green light
Yellow objects absorbs blue light but reflects red and green light
Mixing blue and yellow results in a mixture that absorbs both red and blue light but reflects green light so it looks green
What colours correspond to short, medium and long wavelength light
Blue = short (s) wavelength light
Green = medium (M)
Red = long (L)
What is the trichromatic theory of vision
- Outlines how there are 3 colour receptors (cones) your retina:
1. S cones - 419 nm - blue
2. M cones - 531 nm - green
3. L cones - 558 nm - red
Differentiate between rods and cones
- Both are photoreceptors located in the retina. Cones are responsible for colour vision an are only active in normal light conditions.
- Rods cannot distinguish between colour and are only active at low light levels and thus help with night vision.
- Reason for rods being unable to operate at normal light levels is due to it being too active and habituated and become saturated
What is the munsell colour system
How does colour matching work
Monochromatism
- No functioning cones, only rods are functioning
- leads to complete colour blindness and sees the world in shades of grey
Dichromatism and its three cone types
Lacks in one of 3 cones types
1. Protanopia (protanopes): missing L cone, can’t distinguish between red & green but can distinguish blue & green, blue & red
2. Deuteranopia (Deuteranopes) : missing M cone, can’t distinguish between red & green but can distinguish blue & green, blue & red
3. Tritanopia (tritanopes): missing S cone, can’t distinguish between blue & green but can distinguish red & green, blue & red
Opponent-process theory of colour vision
- Outlines how our perception of colour is a combined effect of cones in our retina and processing by our cortex
- processed then combined in 3 colour opponent channels: red-green, blue-yellow, white-black
- 2 psychological evidence for this: after images and impossible colours
Colour constancy
Light reflected by an object is determined by the product of its reflectance and the illumination
- Reflectance x Illumination = Reflected light
2 psychological evidence for colour opponent channels
- after image
- when viewing a specific colour, the specific cone is stimulate more than the other and become habituated and thus becomes less sensitive
- when then presenting a white stimulus, other cone responds more strongly - impossible colours: some colours cannot be added together - cannot perceive a bluish red