Colour perception

Question 1

Define colour

Answer 1

Colour is what allows us to distinguish 2 surfaces that have the same brightness
Sensation - hue, saturation/ purity and brightness
Physically - wavelength and intensity

Question 2

What are 2 functions of colour?

Answer 2

Signalling and detection

Question 3

What are the physical properties?

Answer 3

Wavelength - blue 450-490nm, red 620-700nm, green 500-575nm
White is a mix of all wavelengths while black is the absense of light

Question 4

What is reflectance?

Answer 4

We see properties that reflect light
Blue - blue and green reflected, yellow -yellow and green reflected, green - green reflected
Reflectance curve is a composition of light reflected by an object

Question 5

What is chromatic light?

Answer 5

Some wavelengths are reflected more than others

Question 6

What is monochromatic light?

Answer 6

Emitted light of only one wavelength

Question 7

What is achromatic light?

Answer 7

Light composition is spread across the visible spectrum, short, medium and long wavelengths

Question 8

What is an additive mix?

Answer 8

The superposition of spotlights adds new wavelengths

Question 9

What is a subtractive mix?

Answer 9

Mixing of pigments subtracts wavelengths (more light is absorbed)

Question 10

What are cone photoreceptors?

Answer 10

Colour perception based on 3 cone receptors in the retina of varying wavelength sensitivity. Maximal absorption of photons at short, medium or long wavelengths

Question 11

What is the density of cones?

Answer 11

Located mostly around the fovea, explaining the poorer colour discrimination in the periphery

Question 12

What is the opponent process theory?

Answer 12

Colour perception based on the combination of responses of receptors. Developed by Ewald Hering (1834-1918)

Question 13

What are ganglion cells?

Answer 13

Cells in the retina that group activity from the 3 cone receptors, creating an opponent code for colour

Question 14

How does colour blindness in one eye work?

Answer 14

Rare case of colour blindness to one eye (deuteranope) - matching colours seen by colour-blind eye to the colours seen in the normal eye

Question 15

What are 3 colour deficiencies?

Answer 15

Protanope - missing long wavelengths
Deuteranope - Missing medium wavelengths
Tritanope - missing short wavelengths

Question 16

What is the Ishihara test for colour deficiencies?

Answer 16

Ishihara pseudo-isochromatic plates can be used to detect colour deficiencies. Numbers are defined by colour contrast

Question 17

What is colour constancy?

Answer 17

Colour constancy is our ability to estimate the reflectance of an object in spite of very different illumination conditions