Color Perception

Question 1

What are the psychological dimensions of light?

Answer 1

Hue - related to wavelength

Saturation - distribution of wavelengths in the light; relates to the purity of hue (how much white is mixed in)

Brightness - intensity; how many photons you are receiving

Question 2

Broadband

Answer 2

includes a lot of different wavelengths, low saturation

e.g. PINK

Question 3

Saturated

Answer 3

primarily one wavelength

e.g. RED

Question 4

Fruit theory of origin and color vision

Answer 4

color allows us to detect and identify objects (e.g. fruit on a tree)

Question 5

What are the 5 types of color phenomena?

Answer 5

1. Color Mixing
2. Contrast
3. Intuitions
4. Color Blindness
5. Color Cancellation

Question 6

Additive vs Subtractive in color mixing

Answer 6

Additive: Adding lights –> creates white

Subtractive: Adding pigments –> creates different colors (black if all)

Question 7

Simultaneous Color Contrast

Answer 7

contrast with background changes how you perceive a color

*both color and the background present simultaneously

Question 8

Successive Color Contrast

Answer 8

• afterimages

* example: seeing bluish circle after staring at orange circle and looking away

Question 9

The Principle of Univarience

Answer 9

the fact that an infinite set of different wave-
length-intensity combinations can elicit exactly the same response from a single type of photoreceptor. One photoreceptor type cannot make color discriminations based on wavelength

problem: two unknowns, one known –> not enough information to solve

Question 10

Why can’t a single receptor type

code for color?

Answer 10

• The brain can only read out the output (i.e., firing rate or
  level of excitation) from this receptor
• A single receptor’s output can be duplicated by any wavelength light (or wavelength combination) merely by scaling (changing intensity).

Question 11

What is trichromacy?

Answer 11

because we have three cone types, we can tell the

difference between lights of many different wavelengths

Question 12

How is a color neurally coded?

Answer 12

• By the firing patterns of the 3 cone types
• Anything that duplicates the outputs of
  the three mechanisms will match the color
  experience

Question 13

Do we have one-to-one mapping from wavelength to cone responses?

Answer 13

• With three cone types: more or less yes

- People with normal vision (three cone types) can distinguish between different wavelengths quite well

Question 14

Do we have one-to-one mapping from cone

responses to wavelengths?

Answer 14

No (metamers)

Question 15

Metamers

Answer 15

Metamers: two physically different stimuli that are perceptually identical

Question 16

Does each pattern of cone responses map to a wavelength?

Answer 16

NO, some colors are experiences from several lights combined

Question 17

Nonspectral hues

Answer 17

colors that can only result from light mixtures (e.g. purple)

*combination of lights activate S and L cones – could not be done by one light alone

Question 18

Spectral hues

Answer 18

colors that can be perceived by a single light (RGB)