Topic 7- Perceiving Colour

Question 1

What are 3 functions of colour perception?

Answer 1

• Can help us identify things
• Can help us classify things
• Can help inform our actions

Question 2

What is object colour?

Answer 2

Determined by the specific wavelength of light that are reflected from, or transmitted through, that object.

Question 3

What are chromatic colours?

3pts

Answer 3

• Colours with hue
• Ex- red, blue, green
• Occurs when some wavelengths are reflected from an object more so than others (selective reflection)

Question 4

What are achromatic colours?

3pts

Answer 4

• Colors without hue
• Ex- white, black, and all shades of grey
• Occurs when light is reflected from an object equally across the spectrum

Question 5

What is selective transmission?

Answer 5

Occurs when only some wavelengths pass through transparent objects, while other wavelengths do not

Question 6

What are the corresponding perceived for wavelengths reflected or transmitted?

• short
• medium
• long and medium
• long
• short, medium, long

Answer 6

Short –> blue
medium –> green
long and medium –> yellow
long–> red
long medium, and short–> white

Question 7

• Mixing paints
• Mixing light

which is adding wavelengths vs subtracting wavelengths

Answer 7

• Mixing paints: subtracting wavelengths
• Mixing light: adding wavelengths

Question 8

What happens when mixing paint ex- blue + yellow paint ?

Combined…

Answer 8

Combined, both paints absorb the same wavelengths they absorbed when they were alone, so only the wavelengths reflected are those reflected by both

Question 9

Colours that appear in the visible spectrum

What are these?

Answer 9

Spectral colours

Question 10

• Colours that do not appear in the visible spectrum
• Are mixtures of spectral colours

What are these?

Answer 10

Nonspectral colours

Question 11

Perception of chromatic colours, or shades/variations of these colours.

What is this?

Answer 11

Hue

Question 12

What is saturation?

3pts

Answer 12

• Amount of “whiteness” added
• More “white” = low saturation
• Desaturated means faded/washed out

Question 13

What is the value (lightness)?

2pts

Answer 13

• The “light-dark” dimension
• Decreases as colours becomes perceptually darker

Question 14

What determines our perception of color in terms of the physiology of color vision? What is trichromacy of color vision?

2pts

Answer 14

-Our perception of colour is determined by the activity of 3 different cone photopigments that have different sensitivities (short wavelengths/blue, medium wavelengths/green/long wavelengths/red)

• If you have all three, you can perceive color

Question 15

What is monochromacy?

2pts

Answer 15

• Complete colour blindless/ “rod-only vision”
• Absence of cone receptors results in the perception of only achromatic colors (white, black and grey)

Question 16

What is dichromacy?

2pts

Answer 16

• Colour vision but only with two pigments present
• Can see some chromatic colours but its hard to distinguish between some colours

Question 17

“Red-green colour blindness”

1% of males, 0.02% of females

• No long-wavelength photopigment

What type of dichromacy is this?

a. protanopia
b. Deuteranopia
c. Tritanopia

Answer 17

Protanopia

Question 18

“Red-green colour blindness”

1% of males, 0.01% of females

• No medium-wavelength photopigment

What type of dichromacy is this?

a. protanopia
b. Deuteranopia
c. Tritanopia

Answer 18

Deuteranopia

Question 19

“Blue-yellow colour blindness”

0.002% of males, 0.001% of females

• No short-wavelength photopigment

What type of dichromacy is this?

a. protanopia
b. Deuteranopia
c. Tritanopia

Answer 19

Tritanopia

Question 20

Our perception of colour is determined by the activity of two opponent mechanisms:

Complete the sentence

How many colors did Hering believe in?

Answer 20

• a blue-yellow mechanism and a red-green mechanism
• Hering proposed that there are four main colors: red, green, yellow, and blue. All other colors are seen as combinations of these four.

Question 21

What is color constancy?

Answer 21

Our perception of an objects color remains relatively constant when the amount of illumination is changed

Question 22

What is lightness constancy?

Why does it occur?

Answer 22

Our perception of an objects lightness (white vs black) remains relatively constant under different intensities of illumination

Occurs because the relative proportion of light being reflected into the eye stays the same regardless of illumination