Colour perception

Question 1

Function of colour percpetion

Answer 1

• Helps humans search for things
• Make judgements
• Spot and identify poison
• Attract a mate

Question 2

Physics of colour

Answer 2

• Visible light is a electromagnetic radiation with wavelengths from 400-700 nm
• White light is a mixture of colours

Question 3

Why do objects appear opaque or transparent

Answer 3

• opaqueness due to light not being able to pass through (red colour = blue light absorbed)
• transparency is determined by the colour it transmits

Question 4

mixing light

Answer 4

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

Question 5

What colours correspond to short, medium and long wavelength light

Answer 5

Blue = short (s) wavelength light
Green = medium (M)
Red = long (L)

Question 6

What is the trichromatic theory of vision

Answer 6

• 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

Question 7

Differentiate between rods and cones

Answer 7

• 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

Question 8

What is the munsell colour system

Question 9

How does colour matching work

Question 10

Monochromatism

Answer 10

• No functioning cones, only rods are functioning
• leads to complete colour blindness and sees the world in shades of grey

Question 11

Dichromatism and its three cone types

Answer 11

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

Question 12

Opponent-process theory of colour vision

Answer 12

• 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

Question 13

Colour constancy

Answer 13

Light reflected by an object is determined by the product of its reflectance and the illumination
- Reflectance x Illumination = Reflected light

Question 14

2 psychological evidence for colour opponent channels

Answer 14

1. 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
2. impossible colours: some colours cannot be added together - cannot perceive a bluish red