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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 Presentation
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Exam next week
• Covers everything about all sensory modalities except hearing
• This includes:visionbalance/touch/taste/smell/
proprioception/theroception
Color Vision• Primary colors
Perceiving Color
Red Green Blue
Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Blue
Wavelength Input Cone Signal to Brain
Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Green
Wavelength Input Cone Signal to Brain
Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red” Red
Wavelength Input Cone Signal to Brain
Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Yellow
Equal Parts Red and Green =
Wavelength Input Cone Signal to Brain
Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Yellow
Equal Parts Red and Green =
Wavelength Input Cone Signal to Brain
Color VisionTrichromatic Theory of Color Vision
“Blue”
“Green”
“Red”
Yellow
Equal Parts Red and Green =
Wavelength Input Cone Signal to Brain
• Problem with Trichromatic Theory:
YELLOW
Theories of Color Vision: Trichromatic Theory
• 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
• 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
• Everything you’ve learned so far is wrong.
• Everything you’ve learned so far is wrong.
• Well, not really wrong, just far from complete.
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
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
What twist did Land do to this paradigm that confounds the
conventional understanding of color mixing?
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
How did Land project the “appropriate” ratio of
wavelengths?
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
medium filter
longfilter
Camera splits image intomaps of “longer” and “shorter” wavelengths
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
What is Land’s interpretation? How do we perceive color?
Land’s interpretation:
• perception of color is a weighing of the ratio of shorter and longer wavelengths
Land’s interpretation:
• perception of color is a weighing of the ratio of shorter and longer wavelengths
Why would the visual system have evolved this way?
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”
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
What is color for?
Does the color of an object remain constant under different lighting conditions?
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
Color Constancy• Because of our
mechanism of color constancy we can even use completely artificial spectra
Color Constancy
• The “color” of objects is independent of the ambient light
Next Time
• ATTENTION!
