exam next week
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Exam next week. Covers everything about all sensory modalities except hearing This includes: vision balance/touch/taste/smell/ proprioception/theroception. COLOR VISION. Color Vision. Perceiving Color. Primary colors. Red Green Blue. Color Vision. - PowerPoint PPT PresentationTRANSCRIPT
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Exam next week
• Covers everything about all sensory modalities except hearing
• This includes:visionbalance/touch/taste/smell/
proprioception/theroception
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Color Vision• Primary colors
Perceiving Color
Red Green Blue
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Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Blue
Wavelength Input Cone Signal to Brain
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Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Green
Wavelength Input Cone Signal to Brain
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Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red” Red
Wavelength Input Cone Signal to Brain
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Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Yellow
Equal Parts Red and Green =
Wavelength Input Cone Signal to Brain
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Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Yellow
Equal Parts Red and Green =
Wavelength Input Cone Signal to Brain
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Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Yellow
Equal Parts Red and Green =
Wavelength Input Cone Signal to Brain
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• Problem with Trichromatic Theory:
YELLOW
Theories of Color Vision: Trichromatic Theory
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• 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
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• Opponent-Process Theory– Red opposes Green– (Red + Green) opposes Blue
• Opponent-Process Theory explains color afterimages – because the “opposite” of blue is
yellow, the “opposite” of green is red, etc.
Theories of Color Vision: Opponent-Process Theory
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• Everything you’ve learned so far is wrong.
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• Everything you’ve learned so far is wrong.
• Well, not really wrong, just far from complete.
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What Newton Found (and everyone believed)
• White light can be split into all wavelengths by a prism
• According to previous theories: two wavelengths combine to yield intermediate color and no others
Red LightGreen Light
Red + Green = YELLOW
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What Newton Found (and everyone believed)
• White light can be split into all wavelengths by a prism
• According to previous theories: two wavelengths combine to yield intermediate color and no others
• Red + Green light can never yield blue
• Blue + Green light can never yield red
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What twist did Land do to this paradigm that confounds the
conventional understanding of color mixing?
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What Land found:
• Two bands (colors) of the spectrum recombine to produce all the possible colors– provided the appropriate relative amount of
each wavelength is projected
transparency slides
Red LightGreen Light
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How did Land project the “appropriate” ratio of
wavelengths?
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Short- and Long- “record”
• Capture two grey-scale images of the scene using filters that allow only the wavelengths you will project
Camera
“short” filter
“Long” filter
film Projector
Object
Image“Long” filter
“short” filter
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medium filter
longfilter
Camera splits image intomaps of “longer” and “shorter” wavelengths
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medium/“green” light
long/“red”light
Projector combines “longer” and “shorter” wavelengths using the maps to get the appropriate amounts of each
Viewer perceivesdesaturated huesincluding blues
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What is Land’s interpretation? How do we perceive color?
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Land’s interpretation:
• perception of color is a weighing of the ratio of shorter and longer wavelengths
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Land’s interpretation:
• perception of color is a weighing of the ratio of shorter and longer wavelengths
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Why would the visual system have evolved this way?
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Why would the visual system have evolved this way?
• Hint: “Within broad limits, the actual values of the wavelengths make no difference, nor does the over-all available brightness of each”
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What is color for?• What is color vision used for?
– Identification - what is this thing?– Discrimination - what other things is this
thing like?– Communication - indicates this thing to
others• But in each case color refers not to the
illuminating light, but to the surface of the object itself
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What is color for?
Does the color of an object remain constant under different lighting conditions?
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Color Constancy• The “color” of objects is independent of the ambient
light – even though light can vary dramatically
Rel
ativ
e In
tens
ity
Wavelength
Rel
ativ
e In
tens
itySunlight Incandescent Light
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Color Constancy• Because of our
mechanism of color constancy we can even use completely artificial spectra
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Color Constancy
• The “color” of objects is independent of the ambient light
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Next Time
• ATTENTION!