read article by land for thursday article by anne treisman coming up in about two weeks
Post on 21-Dec-2015
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• Read article by Land for Thursday
• Article by Anne Treisman coming up in about two weeks
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
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
Ishihara Color Plates can indicate color blindness
Color VisionTheories of Color Vision
DON’T DO THIS !
…~3% of male readers will have trouble seeing it!
Color VisionTheories of Color Vision
But this is OK.
Color VisionTheories of Color Vision
So is this.
Color VisionTheories of Color Vision
Even this is good.
Theories of Color Vision
• Problem with Trichromatic Theory:
Theories of Color Vision
• Problem with Trichromatic Theory:
YELLOW
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 vs. Subtractive
There are two different ways to mix colors.
• Additive vs. Subtractive
What do you get if you use a prism to combine all wavelengths of light?
• Additive vs. Subtractive
What do you get if you use a prism to combine all wavelengths of light?
• Additive vs. Subtractive
What do you get if you mix a bunch of paint?
• Additive vs. Subtractive
What do you get if you mix a bunch of paint?
• Additive vs. Subtractive
• Additive mixing is most intuitive:
ADD wavelengths:
red+green = yellowred+blue = magentablue+green = cyanred+green+blue=white
Exploring Additive Mixing
• use color sliders to adjust R,G,B values
• What color can only exist as a metamer (an additive mixture of wavelengths)? In other words, what color cannot be made with a single wavelength?
• What color can only exist as a metamer (an additive mixture of wavelengths)? In other words, what color cannot be made with a single wavelength?
Magenta
Think about why!
• Subtractive mixing is much less intuitive (but much more common)
• Subtractive mixing happens when we mix pigments (paint) together
• Different pigments subtract different wavelengths:– red subtracts all but red, blue all but blue,
green subtracts blue and red, etc…
• Example: blue + yellow = green
Technically it’s called “cyan”
• The result of a mixture depends on what wavelengths don’t get absorbed by the two pigments
wavelength
Am
ount
of
refl
ecti
on
blue green yellow red
• Both yellow and blue pigments reflect a bit of green
wavelength
Am
ount
of
refl
ecti
on
blue green yellow red
• Subtractive mixing is commonly used in color printers
• 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 color is this box?
• What color is this box?