Color Flashcards
How much of the electromagnetic spectrum do we see?
between 400-700nm
What are photoreceptors?
Photoreceptors are tuned to respond to a particular wavelength/color.
What is the problem of univarience?
Two completely different colors elicit the same response.
Changing intensity makes it even worse.
What stimuli to photoreceptors respond to?
Photoreceptors respond to both wavelength and intensity.
What is intensity?
brightness
Can we see light with only one kind of photoreceptors?
NO
What are the two type of light levels?
Photopic and Scotopic
What is photopic light?
Bright sunlight and indoor lighting.
Stimulates cones and saturates rods.
What is scotopic light?
Moonlight, dim indoor lighting.
Stimulates rods, but too dim for cones.
What type of photoreceptors respond best to scotopic light?
Rods-
All rods contain the photopigment rhodopsin.
All rods have the same sensitivity to various wavelengths of light.
What type of photoreceptors respond best to photopic light?
Cones are active in photopic light.
There are three types of cones, each with different photopigment, sensitive to different wavelengths.
What are the three types of cones in trichromacy?
l-cones
m-cones
s-cones
What are l cones?
Preferentially tuned to long wavelengths
“red” cones
What are m cones?
Preferentially tuned to middle wavelengths
“green” cones
What are s cones?
Preferentially tuned to short wavelengths
“blue” cones
What is color matching?
- theory is if you have the right shades of 3 colors- (red,green,blue) you can make any color
What are metamers?
Different mixtures of wavelengths that look identical
What is additive color mixing?
If light A and light B are both reflected from a surface to the eye, your perception is based on the addition of the two.
What is subtractive color mixing?
Mix Pigment A and Pigment B.
A absorbs some wavelengths and reflects others.
B absorbs some wavelengths and reflects others.
What you see is what is left after each pigment subtracts some.
How do you describe color?
any color can be specified using three numbers
What is RGB colorspace?
Defined by the amount of Red, Green, and Blue.
Long, medium, and short wavelength lights.
What is HSB Color Space?
Hue: chromatic (color) aspect of light.
Saturation: chromatic strength of a hue.
Brightness: distance from black in color space.
What are ‘legal colors’?
Only some color combinations are allowed.
What are the legal and illegal color combinations?
Legal”: bluish-green (turquoise, aqua) reddish-yellow (orange) bluish-red (purple) “Illegal”: reddish-green bluish-yellow
What is the opponent color theory?
Perception of color is based on the output of three mechanisms, each of them based on an opponency between two colors:
What are some of the opponent color?
red-green
blue-yellow
black–white
How do we process color?
Cells in the LGN respond to combinations of signals from retinal ganglion cells.
What is a color opponent cell?
Color-opponent cell:
A neuron whose output is based on a difference between sets of cones.
Same wiring as lateral inhibition.
How do neurons in the LGN respond to the Color opponent cells?
Some are excited by M-cones in the center and inhibited by L-cones in the surround (and vice versa): red-green
Others are excited by S-cones in the center and inhibited by (M+L)-cones in the surround (and vice versa): blue-yellow.
What is selective adaptation?
We can observe opponent-cells using adaptation,
What is an afterimage?
A visual image seen after a stimulus has been removed.
What is a negative afterimage?
An afterimage whose polarity is the opposite of the original stimulus white image → dark afterimage red image → green afterimage blue image → yellow afterimage (and vice versa)
How many people are effected by color blindness?
8% of male population
0.5% of female population
What are the three types of colorblindness?
protanopia
deuteranopia
tritanopia
What is protanopia?
Absence of L-cones
1.3% of males, 0.01% of females
What is deuteranopia?
Absence of M-cones
1.2% of males, 0.01% of females
What is tritanopia
Absence of S-cones
0.001% of males, 0.03% of females
What is color anomalous?
L- and M-cones that are so similar that they can’t make discriminations.
What is a cone monochromat?
Only one cone type; truly color-blind.
What is a rod monocromat?
No cones at all.
What is cultural relativism?
Basic perceptual experiences (e.g., color perception) may be determined in part by the cultural environment.
What is an unrelated color?
A color that can be experienced in isolation.
What is a related color?
A color that is seen only in relation to other colors.
e.g., brown, gray
A “gray” patch in complete darkness appears white
What is an illuminant?
The light that illuminates a surface
What is color consistency?
The tendency of a surface to appear the same color under a fairly wide range of illuminants.
