lecture 9

Question 0

Role of Color

Answer 0

Finding Fruit
Finding mates

Highlights/draws attention

Question 1

Strobe lights

Answer 1

destroys sense of motion

Question 2

Color wavelength

Answer 2

gamma-> x-rays-> UV-> visible-> infared-> radar-> broadcast-> AC circuits

Humans visible light (400nm to 700nm)
- different organisms sensitive to diff wavelengths

Question 3

Color of object

Answer 3

a product of illumination and the reflectance of the object
albedo- ability of an object to reflect light

depends on the surface of the object AND the source of illumination (light source).

Question 4

Composition of light equation

Answer 4

light from surface = illumination x reflectance

lettuce looks lighter under incandescent light than under sunlight

Question 5

Sodium lamp

Answer 5

one wave lamp
grayscale/ sepia
-problems with food, clothes, art

Case of Mr I- cortical color blindness

• loss color perception, memory, imagination
• shadows = objects
• can only name colors

Question 6

Color Coded theory

Answer 6

Trichromatic theory

opponent process theory

Question 7

Young-Helmholtz Trichromatic Theory

Answer 7

•   only 3 cones, each broadly tuned to wavelength
•   Perceived color depends on the relative strength of their activation
•   Any color can be formed by combining different amounts of 3 primary colors (corresponding to 3 cone types).

Question 8

Trichromatic Theory: Cones ratios and color

Answer 8

Patterns of trichromatic cones differs from person to person

Perceived color varies with ratio of responses of the three cones

• Infinite set of possible wavelength distributions
• Human vision measures only 3 cone values
• non-invertible: can’t recover the wavelength distribution

Question 9

Metamers

Answer 9

different spectra-> same color

Question 10

Color addition & Subtraction

Answer 10

Color addition for lights: response of visual system

• Red + Green = yellow
• Blue + Red = purple
• blue and green = teal
• red + blue + green = white

Color subtraction for paints: physics of stimulus

Question 11

Ewald Hering

Answer 11

Colors organized in pairs of opponent colors
Red-green, blue-yellow, white-black
Evidence: after images, response of neurons that code opposite colors

Question 12

How does afterimage work?

Answer 12

Red on, Green off receptive field

• White: Neuron fires at baseline signals white
• Red Stimulation: Neuron fires above baseline signals red
• White: Neuron fires below baseline signals green

Red off, Green on receptive field

• White: Neuron fires at baseline signals white
• Red Stimulation: Neuron fires below baseline signals red
• White: Neuron fires above baseline signals green