9. Color Perception · 2017-10-10 · 10/10/2017 4 Perceiving Color • Subtractive color mixing...
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10/10/2017 1 Color Vision Color • Secondary quality • Colors help discriminate objects • Colors have semantic associations
Transcript of 9. Color Perception · 2017-10-10 · 10/10/2017 4 Perceiving Color • Subtractive color mixing...
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Color Vision
Color
• Secondary quality
• Colors help discriminate objects
• Colors have semantic associations
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Color
• Colors can elicit emotions (Elliot & Niesta, 2008)
Perceiving Color
• Correlation between wavelength and color
• 620 – 700 nm = red
• 590 – 620 nm = orange
• 575 – 590 nm = yellow
• 500 – 575 nm = green
• 450 – 490 nm = blue
• 400 – 450 nm = violet
• Light waves themselves are colorless
• Monochromatic light
• Polychromatic light
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G
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Perceiving Color
• Perceptual dimensions of color
• Visible spectrum is continuous (400 nm – 700 nm)
• We can distinguish hundreds of colors
• But, we perceive colors categorically
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Perceiving Color
• Perceptual dimensions of color
• Hue
• Brightness
• Saturation
Perceiving Color
• Perceptual Color Categories
• Primary colors
• Secondary colors
• Tertiary colors
Perceiving Color
• Additive color mixing
• Results from a mixture of light beams onto a single location
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Perceiving Color
• Subtractive color mixing
• Results mixture of pigments
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Yellow
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Yellow + Blue
Perceiving Color
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Trichromatic Theory
• Young-Helmholtz Theory
• Cones are involved with color perception
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Trichromatic Theory
• Problem of Univariance
• Any one cone cannot discriminate color
• Same output to different wavelengths
Trichromatic Theory
• There are three types of cones on the retina (S, M, L)
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Trichromatic Theory
• Color perception is based on the unique output across the three types of cones
• Problems with Young-Helmholtz?
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LGN Color Channels
• Luminance Channel
White-Black (L + M)
• Chromatic Channels
• Red-Green (L - M)
• Yellow-Blue [S - (L + M)]
S M L
Y- B+ R- G+ W+ B-Y+ B- R- G+ W- B+
Activation
Inhibition
Color-Opponent Process Theory
• “Opposing responses” from LGN channels
• Illegal color combinations
• Negative afterimages
• Simultaneous color contrast
Color-Opponent Process Theory
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Color-Opponent Process Theory
Color Vision Deficiencies
• Found in ~8% of males and ~0.5% of females
• Ishihara Colorblindness Plates
• Color Matching Experiments
Color Deficiencies• Cone dichromatism
• Deuteranopia
• Protanopia
• Tritanopia
• Unilateral dichromatism
• Monochromatism
• Cone monochromat
• Rod monochromat
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Perception of Color and Culture?
• Can culture influence perception?
• Davidoff, Fonteneau & Fagot (2008)
• Himba tribe
• Global-local choice task
Culture % Global Choices
Western 86.01 %
Himba 22.81 %
“Standard”
“Global Match”“Local Match”
Perception of Color and Culture?
• Eleanor Rosch (1972)
• Dani tribe (New Guinea) have two color words:
• mola = light
• mili = dark“Remember”
“Test”
‘mola’ ‘mola’
‘mola’ ‘mola’ ‘mola’‘mili’
Color Assimilation
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Shadows
• Which parallelogram appears darker?
Shadows
Shadows
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Shadows
• Which dotted square appears to be darker?
Shadows
• Visual system takes into account “shadows” caused by the cylinder
Shadows
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Cornsweet Illusion
Cornsweet Illusion
McCollough Effect
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Color Constancy • Why does a colored surface appear the same under
different Illuminants?
Should look very different
Color Constancy
• R = I x S
• R: “Wavelengths Hitting Retina”
• I: “Wavelengths in Illuminant”
• S: “Wavelengths from Surface”
• Visual system adapts to
(discounts) illuminant
• Emphasis placed on unique
wavelengths from the surface
![A Theory of Non-Subtractive DitherEarly investigations into non-subtractive dither per se were conducted by one of the authors, Wright [10], in 1979, resulting in discovery of many](https://static.fdocuments.us/doc/165x107/5ea5ef6eccf42824383f7cfc/a-theory-of-non-subtractive-early-investigations-into-non-subtractive-dither-per.jpg)
