Wavelength and Color Recall that light is electromagnetic radiation

Wavelength and Color Recall that light is electromagnetic radiation Light waves have a frequency/wavelength

Wavelength and Color Recall that light is electromagnetic radiation Light waves have a frequency/wavelength Frequency/wavelength is the physical property that corresponds (loosely) to the perception called color

Color Vision Different wavelengths correspond roughly to the “colors” of the spectrum Wavelength and Color

Color Vision White light is a mixture of wavelengths –prisms decompose white light into assorted wavelengths Wavelength and Color

Color Vision White light is a mixture of wavelengths –prisms decompose white light into assorted wavelengths –likewise, adding all wavelengths together recovers white light What happens if you mix several different paints together? Wavelength and Color

Color Vision Objects have different colors because they reflect some but not all wavelengths of light –the surfaces of objects are like filters that selectively absorb certain wavelengths Wavelength and Color

Color Vision Primary colors Perceiving Color What are the primary colors?

Color Vision Primary colors Perceiving Color Red Green Blue

Color Vision Primary colors Perceiving Color What makes them primary?

Color Vision Primary colors Every color (hue) can be created by blending light of the three primary colors in differing proportions Perceiving Color

Color Vision Primary colors Every color (hue) can be created by blending light of the three primary colors in differing proportions Led to prediction that there must be three (and only three) distinct color receptor types Perceiving Color

Color Vision Perceiving Color Four absorption peaks in retina: 3 cone types plus rods Absorption/Cone response

Color Vision Theories of Color Vision “Blue” “Green” “Red” Blue Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Green Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Red Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision Trichromatic theory of color vision: –brain interprets the relative amounts of signaling from each of these cone types

Color Vision Theories of Color Vision Trichromatic theory of color vision: –brain interprets the relative amounts of signaling from each of these cone types This means that some colors can be matched by a pair of wavelengths –metamers: colors that have no definite single wavelength (e.g. yellow)

Color Vision Theories of Color Vision Trichromatic theory of color vision: –brain interprets the relative amounts of signaling from each of these cone types This means that some colors can be matched by a pair of wavelengths –metamers: colors that have no definite single wavelength (e.g. yellow) This also means that any color can be matched by mixing (not more than) three different wavelengths

Color Vision Theories of Color Vision Trichromatic Theory can explain colorblindness: –most of us are trichromats –someone missing one of the three cone types is a dichromat –someone missing two is a monochromat –someone missing all cone types is called a rod monochromat (very poor vision!)

Color Vision Theories of Color Vision Trichromatic Theory can explain colorblindness: –dichromats have only two primaries: any color they can see can be matched with differing proportions of the two wavelengths that they are sensitive to

Color Vision Theories of Color Vision Trichromatic Theory can explain colorblindness: –dichromats have only two primaries: any color they can see can be matched with differing proportions of the two wavelengths that they are sensitive to –most common is deuteranopia (~3% of men, <1% of women) - missing “green” cones

Color Vision Theories of Color Vision Trichromatic Theory can explain colorblindness: –dichromats have only two primaries: any color they can see can be matched with differing proportions of the two wavelengths that they are sensitive to –most common is deuteranopia (~3% of men, <1% of women) - missing “green” cones –cannot see difference between reds and greens

Color Vision Theories of Color Vision Ishihara Color Plates can indicate color blindness

Color Vision Theories of Color Vision DON’T DO THIS ! …~3% of male readers will have trouble seeing it!

Color Vision Theories of Color Vision But this is OK.

Color Vision Theories of Color Vision So is this.

Color Vision Theories of Color Vision Even this is good.

Color Vision Theories of Color Vision But this probably isn’t!

Theories of Color Vision Problem with Trichromatic Theory:

Theories of Color Vision Problem with Trichromatic Theory: YELLOW

Theories of Color Vision Problem with Trichromatic Theory: –most people categorize colors into four primaries: red, yellow, green, and blue –some colors simply cannot be perceived as gradations of each other redish green !? blueish yellow !?

Theories of Color Vision Opponent-Process Theory –color is determined by outputs of two different continuously variable channels: red - green opponent channel blue - yellow opponent channel

Theories of Color Vision Opponent-Process Theory –Red opposes Green –(Red + Green) opposes Blue Opponent-Process Theory explains color afterimages