Read article by Land for Thursday Article by Anne Treisman coming up in about two weeks

Color Vision Theories of Color Vision “Blue” “Green” “Red” Blue Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Green Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Red Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision Trichromatic theory of color vision: –brain interprets the relative amounts of signaling from each of these cone types

Color Vision Theories 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 Vision Theories 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 Vision Theories 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 Vision Theories 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 Vision Theories 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 Vision Theories 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 Vision Theories of Color Vision Ishihara Color Plates can indicate color blindness

Color Vision Theories of Color Vision DON’T DO THIS ! …~3% of male readers will have trouble seeing it!

Color Vision Theories of Color Vision But this is OK.

Color Vision Theories of Color Vision So is this.

Color Vision Theories 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 = yellow red+blue = magenta blue+green = cyan red+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?

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 Amount of reflection blue greenyellowred

Both yellow and blue pigments reflect a bit of green wavelength Amount of reflection blue greenyellowred

Subtractive mixing is commonly used in color printers

Everything you’ve learned so far is wrong.

Well, not really wrong, just far from complete.

What color is this box?