Embed Size (px)
Citation preview
What Newton Found (and everyone believed)
• White light can be split into all wavelengths by a prism
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” Red
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
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 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?
What is color for?
• What is color vision used for?– Identification - what is this thing?– Discrimination - what other things is this like?– Communication - indicates this thing to others
What is color for?
• What is color vision used for?– Identification - what is this thing?– Discrimination - what other things is this 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?
• What is color vision used for?– Identification - what is this thing?– Discrimination - what other things is this 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
Does the color of an object remain constant under different lighting conditions?
Color Constancy
• The “color” of objects is independent of the ambient light
– yellow bananas and green leaves look yellow and green regardless of whether they are viewed in direct sunlight or by the light of a fire
Next Time
• ATTENTION!
![IEEE SEM - Wavelengths · 2018. 12. 6. · April 1, 2015 [IEEE SEM - WAVELENGTHS] Wavelengths. Section Chair’s Message . I received several responses to last month’ Chair’s](https://img.pdfslide.net/doc/110x75/60023b09958d664df8767988/ieee-sem-wavelengths-2018-12-6-april-1-2015-ieee-sem-wavelengths-wavelengths.jpg)
