COGS 101A Lecture Notes - Lecture 9: Trichromacy, Subtractive Color, Color Vision
● Color Vision
○ Why is it important
■ Food foraging (Color opponency: distinguishing objects, exp. Apple
compared to leaves)
● Calorie dense foods tend to be colored
● Rotten for ripe food
■ Perceptual organization: similar elements become group together and
separated from their background
■ Additional dimensional …
■ Crypsis (Camouflage)
■ Aposematism (warning)
■ Visibility
■ Signaling (advertising something, reproductive fitness)
○ Color perception
■ Color: not the physical property of object, not a direct property of light
waves, entirely a creation of our NS
● Hue (a quality)
○ Color wheel; red, green, blue
● Saturation (purity of light)
○ Strength of hue: red to pink
● Intensity (luminance, value, brightness)
○ Transparency, brightness
■ Vision and Light
● Color results from how light interacts with our sensory receptors
■ White light
● Comprised of all the wavelengths
■ Ways of seeing color
● Selective reflectance
○ determines color of solids
● White light
○ Comprised of all the wavelengths
● Selective transmission
○ Determines color of clear object, what wavelength (red,
blue, etc) is allowed to pass through
● Pigment
○ What mostly determines color, which have wavelength
selective absorption
● Nanoscale structures
○ Constructive interference, all other colors pass through
there and cancel each other out except for blue because of
the wavelength
● Reflectance curve
○ percent of each wavelength reflected
Document Summary
Food foraging (color opponency: distinguishing objects, exp. Calorie dense foods tend to be colored. Perceptual organization: similar elements become group together and separated from their background. Color: not the physical property of object, not a direct property of light waves, entirely a creation of our ns. Color results from how light interacts with our sensory receptors. Determines color of clear object, what wavelength (red, blue, etc) is allowed to pass through. What mostly determines color, which have wavelength selective absorption. Constructive interference, all other colors pass through there and cancel each other out except for blue because of the wavelength. Chromatic colors: when some wavelengths reflected more than others. Achromatic colors: when light reflected equally across spectrum; uniformity in spectrum. Subtractive color mixing: adding pigments reflects fewer wavelengths. Additive color mixing: adding lights reflects more wavelengths. Idea that human color vision depends on three different receptor mechanisms-- proposed long before we knew that we had three cones (mid 1800s)
