read land article for thursday test starts wednesday of next week!!!!
Post on 20-Dec-2015
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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
• 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 VisionPerceiving Color• Four absorption peaks in retina: 3 cone types plus rods
Abs
orpt
ion/
Con
e re
spon
se
Color VisionTheories of Color Vision
“Blue”
“Green”
“Red”
Blue
Wavelength Input Cone Signal to Brain
Color VisionTheories of Color Vision
“Blue”
“Green”
“Red”
Green
Wavelength Input Cone Signal to Brain
Color VisionTheories of Color Vision
“Blue”
“Green”
“Red”
Yellow
Equal Parts Red and Green =
Wavelength Input Cone Signal to Brain
Color VisionTheories of Color Vision
“Blue”
“Green”
“Red”
Yellow
Equal Parts Red and Green =
Wavelength Input Cone Signal to Brain
Color VisionTheories of Color Vision
“Blue”
“Green”
“Red”
Yellow
Equal Parts Red and Green =
Wavelength Input Cone Signal to Brain
Color VisionTheories of Color Vision• Trichromatic theory of color vision:
– brain interprets the relative amounts of signaling from each of these cone types
Color VisionTheories 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 VisionTheories 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 VisionTheories of Color Vision• Trichromatic Theory can explain some
aspects of 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 VisionTheories of Color Vision• Trichromatic Theory can explain some aspects of
colorblindness:
– dichromats have only two primaries: any color they can see can be matched with differing proportions of the two wavelengths to which they are sensitive
Color VisionTheories of Color Vision• Trichromatic Theory can explain some aspects of
colorblindness:
– dichromats have only two primaries: any color they can see can be matched with differing proportions of the two wavelengths to which they are sensitive
– most common is deuteranopia (~3% of men, <1% of women) - missing “green” cones
Color VisionTheories of Color Vision• Trichromatic Theory can explain some aspects of
colorblindness:
– dichromats have only two primaries: any color they can see can be matched with differing proportions of the two wavelengths to which they are sensitive
– most common is deuteranopia (~3% of men, <1% of women) - missing “green” cones
– cannot see color difference between reds and greens - but they can see luminance difference
Color VisionTheories of Color Vision
DON’T DO THIS !
…~3% of male readers will have trouble seeing it!
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 !?
– It is as if these colors are opposites
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
Color Vision
• White light is a mixture of wavelengths– prisms decompose white light into assorted
wavelengths– OR recompose a spectrum into white light
Wavelength and Color
• Additive mixing is most intuitive:
ADD wavelengths:
red+green = yellowred+blue = magentablue+green = cyanred+green+blue=white