Color Vision Flashcards
Hue
The color: Hue is related to wavelength (relation is not simple)
Saturation
The distribution of light, The more pure, the more saturation, Many different wavelengths is referred to as being broadband
Brightness
The intensity of light, Light to dark
Functions of color vision
having color vision makes it easier to discriminate good food from bad food, obj detection, obj recognition and identification
Color mixing: Additive
Adding lights. A mixture of lights. If light A and light B are both reflected from a surface to the eye, in the perception of color the effects of those two lights add together.
color mixing: Subtractive
Adding pigments. A mixture of pigments. If pigments A and B mix, some of the light shining on the surface will be subtracted by A. and some by B. Only the remainder will contribute to the perception of color. Each pigment reflects a certain band of wavelengths
Color contrast: simultaneous
Your perception of an object may be different due to different backgrounds OR a color in one part in the visual field affects your perception of another color
Color contrast: successive
Referred to as Afterimages, think of when you stare at an image for a long time and it gives an “after effect” when you see another image.
Negative afterimages
an afterimage whos polarity is the opposite of the original stimulus. Light stimuli produce dark negative afterimages. Colors are complementary; for example, red produces green, and yellow produces blue.
Color blindness- color deficiency observation
People who are color-blind to red are also color-blind to green.
People who are color-blind to blue are also color-blind to yellow.
color blindness- Herring’s Observation
Types of Color deficiencies – Red-green color blindness – Blue-yellow color blindness; Color-normal people can’t see red-green together, nor blue-yellow together
Wavelength sensitivity of cones
S-cones = SHORT wavelengths (blue cones) M-cones = MIDDLE wavelength (green cones) L-cones = LONG wavelengths (red cones)
The problem of univariance:
different wavelength-intensity combinations can elicit exactly the same response from a single type of photoreceptor. Need multiple types to discriminate. (Univariance = there’s only 1 quantity (one dimension of input and one of output) that can vary).
Theories for color perception
trichromatic & opponent
Trichromatic theory
With three cone types we can tell the difference between lights of different wavelengths.
Evidence for the theory
3 Receptors →3 primary color sensations: Blue, Green, Red. (Yellow is claimed to be combination of green & red)
color matching experiment
By adjusting proportions of 3 wavelengths it’s possible to match the color of comparison to a single wavelength testfield, but need at least three wavelengths to match all wavelengths in spectrum
Opponent color theory
The theory that perception of color is based on the output of three mechanisms, each of them on an opponency between two colors: red–green
blue–yellow
black–white
Evidence for the theory
Better at explaining simple and complex colors, contrast, exclusivity (no bluish yellow), and the color yellow itself; Physiological evidence, Opponent neurons: B+Y-, Y+B-, G+R-, R+G-
color phenomena and our intuition
- Color Mixing 2. Contrast
- Intuitions
- Color Blindness
- Color Cancellation
hue cancellation experiment
Famous experiments: Hurvich & Jameson (1957) Cancellation experiments estimated the strength of each mechanism along the wavelength dimension.
Unique hues
any of four colors that can be described w/only a single color term: red, yellow, green, blue. (other colors (e.g., purple or orange) can also be described as compounds (reddish blue, reddish yellow).
Putting the two theories together
As an account of color experience, Young Helmholtz theory is incorrect; • Color vision is trichromatic, however, in an important sense: based on 3 mechanisms at the retina
A two-stage processing
The FIRST stage of color processing is captured well by the trichromatic theory (color matching), and the SECOND stage of color processing captured well with the opponent-process theory (afterimages, simultaneous contrast).
