Chapter 5-the Perception Of Color Flashcards
Color descriptions use how many attributes and what are they
3; hue, brightness, saturation
Hue
“Color”; chromatic aspect of light
Saturation
Amount of hue present in light; how deep of a color, how pure it is; the less saturated it is the more white it is
Brightness
Amount of light, less of any wavelength changes it to blacker; black-white achromatic axis
How many axes
2; red vs green and blue vs yellow
RBG
Different color space to define wavelength present
Subtractive color mixing
Mixture of pigments; if pigment a and b mix, some of the light shining on the surface will be subtracted by a and some by b. The remainder contributes to the perception of color. See in paining, mixing color
When you subtract all wavelengths you see what color
You get black
White light has what wavelength color
All colors
Mixing blue and yellow make green-how
High pass filter for yellow, band pass filter for blue, the ones that are the same make green
Color printer cartridge has what colors
MCY (magenta, cyan, yellow); subtractive
Computer screen has what wavelengths
Red, green, blue; additive
Additive color mixing
A mixture of lights; if a and b are both reflected from a surface to the eye, in the perception of color, the effects of those two lights add together
When all the wavelengths are added together, what color
Or when just red, blue and green added
White
S cones
Detect short wavelengths (420-ish), blue
M cones
Detect medium wavelengths (535-ish) green
L cones detect
Long wavelengths (565-ish) red
Cone photoreceptors aren’t called by the color because
They absorb all colors, just more sensitive to some rather than others
Problem of univariance
Infinite set of different wavelength intensity combinations can elicit exactly the same response from a single type of photoreceptor
According to the problem of univariance, one type of photoreceptor ___ detect color discriminations based on wavelength
Cannot
With univariance, don’t know what stimulated, just how to ____
Respond
Photopic
Light intensities that are bright enough to stimulate the cone receptors and bright enough to saturate the rod receptors
Scotopic
Light intensities that are bright enough to to simulate rods but too dim to stimulate cones
With three cone types, we can tel the ____ amount of different between individual lights of different wavelengths
Relative
Under Photopic conditions, what cones are active
S, m and l
Trichromacy (young helmholtz theory)
The color of any light is defined in our visual system by the relationships of the outputs of three receptor types; relative outputs of 3 receptor types, how strongly 1 responds in relation to the others
Additive mixture uses what material
Metamers
Metamer
Pairs of light containing different wavelengths that appear identical; mixtures that look the same but have different wavelengths
Test color containing a single wavelength can be matched subjectively to another color containing a ____ of primary wavelengths at different intensities
Mixture
Normal observers need how many primaries to match test color
3
To explain Metamers, use what curve
Curve of chromatic sensitivity for different cone combos; one side is excitatory and one is inhibitory (positive and negative)
Can create curves of chromatic sensitivity for ___ cone combos
Different; single wavelength gives pure hue
How many colors result from a single wavelength
3, yellow green and blue
Green/red and blue/yellow chromatic sensitivity curve create
3 primaries and range of colors
Opponent color theory (psychophysics example)
The theory that perception of color is based on the output of three mechanisms, each of them based on an opponent between two colors; red-green, blue-yellow, black-white
LGN has cells that are cone opponent cells
Neurons whose output is based on a difference between sets of cones; center surround (red center, green surround, etc); overall color presence
Cone opponent cells subtract ____ of cone input from another
One type
In the primary visual cortex, double opponent color cells are found for the first time
More complicated, combine the properties of two color opponent cells from LGN; spots of color
Single opponent cells (cone opponent cells)
Red vs green
Double opponent cells
R-/G+ in surround, R+/G- in center; more red in center and green in the background gives greater response
Color constancy
The tendency of a surface to appear the same color under a fairly wide range of illuminants; see the same color even in a wide range of light sources
To achieve color constancy, we must discount the ____ and determine what the true color is regardless of how it appears
Illuminant
Illuminant
Light that illuminates a surface
Physical constraints make constancy possible
Intelligent guesses about Illuminant, assumptions about light sources, assumptions about surfaces
Guesses about Illuminant
Day outside-blue
Inside-yellow
Take into account response across entire retina (horizontal/amacrine)
Assumptions about light sources
From above, consistent over space
Assumptions about surfaces
Maintain constant surface reflect ants, consistent with prior experience
Spectral power distribution
Physical energy in a light as a function of wavelength
Color blindness
8% of men and .5% of females
Deuteranope
Color blindness from loss of M cones (r/g)
Protanope
Color blindness from loss of L cones; r/g
Tritanope
Color blindness from loss of S cones; b/y
Cone monochromat
Have just one cone type; completely color blind; can’t tell color difference, just a difference in light and dark levels
