color vision

color

not a (single unique) physical property of things in the world, but a psychophysical phenomenon that depends of the complex relationships between a variety of disparate physical features

light detection, wavelength/spectrum discrimination, appearance

three steps to color vision

light detection

we must detect the light- our photoreceptors are only sensitive to a narrow bad of frequencies//wavelengths

wavelength/spectrum discrimination

must be able to differentiate between lights composed of different wavelengths or spectra (mixtures of wavelengths)

appearance

must be able to perceive the colors of objects and surfaces consistently under changing lighting conditions

spectral

referring to the wavelength of light

illuminant

the light source

power spectrum

description of the amount of energy (power) at each wavelength

absorption spectrum

describes photoreceptor response as a function of light wavelength/frequency

principle of univariance

the response of ant single photoreceptor is consistent with an infinite number of different wavelength-intensity combinations; a single type of photoreceptor cannot make spectral/color discriminations

scotopic

very dim

trichromacy

theory that the color of any light is defined in our visual system by the relationships of three numbers, the outputs of three receptors types now known to be the three cones; also known as the Young-Helmholtz theory- developed before scientists were able to measure the absorption spectra of photopigment or the response of the photoreceptors

non-spectral hues

percepts that cannot be produced by any single-wavelength

additive color mixing

a mixture of lights with different spectra; if A and light B are both reflected from a surface to eye, in the perception of color, the effects of those two lights add together

subtractive color mixing

a mixture of pigments; if pigment A and pigment B mix, some of the light shining on the surface will be subtracted by A and some by B. only the remainder contributes to the perception of color

color space

three-dimensional space that describes all colors

gamut

describes what colors any set of three lights can reproduce

opponent color theory

claims that perception of color is based on the output of three channels, each based on an opponency between two colors

illuminant

defined by power spectrum- amount of light energy at each wavelength

object

defined by reflectance function; percentage of light at each wavelength that is reflected

cones

defined by absorption spectrum; each cone class adds up light energy according to its absorption spectrum

rgc responses

defined by three spectral measurements; convey all color information to bran via opponent channels

anomalous trichromacy

one cone has abnormal cone pigment with absorption shifted closer to another (usually m shifted toward l)

protanopia

missing l cone/pigment

deuteranopia

missing m cone/pigment

tritanopia

missing s cone/pigment