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

2. Color Vision Primary colors Perceiving Color What are the primary colors?

3. Color Vision Primary colors Perceiving Color Red Green Blue

4. Color Vision Primary colors Perceiving Color What makes them primary?

5. Color Vision Primary colors Every color (hue) can be created by blending light of the three primary colors in differing proportions Perceiving Color

6. Color Vision Primary colors Every color (hue) can be created by blending light of the three primary colors in differing proportions Led to prediction that there must be three (and only three) distinct color receptor types Perceiving Color

7. Color Vision Perceiving Color Four absorption peaks in retina: 3 cone types plus rods Absorption/Cone response

8. Color Vision “Blue” “Green” “Red” Blue Wavelength InputCone Signal to Brain Theories of Color Vision: Trichromatic Theory

9. Color Vision “Blue” “Green” “Red” Green Wavelength InputCone Signal to Brain Theories of Color Vision: Trichromatic Theory

10. Color Vision “Blue” “Green” “Red” Red Wavelength InputCone Signal to Brain Theories of Color Vision: Trichromatic Theory

11. Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain Theories of Color Vision: Trichromatic Theory

12. Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain Theories of Color Vision: Trichromatic Theory

13. Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain Theories of Color Vision: Trichromatic Theory

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

15. 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) Theories of Color Vision: Trichromatic Theory

16. 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 Theories of Color Vision: Trichromatic Theory

17. use color sliders to adjust R,G,B values

18. 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?

19. Magenta Think about why!

20. 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!)

21. 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

22. 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 Theories of Color Vision: Trichromatic Theory

23. 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 Theories of Color Vision: Trichromatic Theory

24. Color Vision Ishihara Color Plates can indicate color blindness Theories of Color Vision: Trichromatic Theory

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

26. Color Vision But this is OK. Theories of Color Vision: Trichromatic Theory

27. Color Vision So is this. Theories of Color Vision: Trichromatic Theory

28. Color Vision Even this is good. Theories of Color Vision: Trichromatic Theory

29. Problem with Trichromatic Theory: Theories of Color Vision: Trichromatic Theory

30. Problem with Trichromatic Theory: YELLOW Theories of Color Vision: Trichromatic Theory

31. 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: Trichromatic Theory

32. 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

33. Opponent-Process Theory –Red opposes Green –(Red + Green) opposes Blue Opponent-Process Theory explains color afterimages Theories of Color Vision: Opponent-Process Theory

34. 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

35. Additive vs. Subtractive There are two different ways to mix colors.

36. Additive vs. Subtractive What do you get if you use a prism to combine all wavelengths of light?

37. Additive vs. Subtractive What do you get if you use a prism to combine all wavelengths of light?

38. Additive vs. Subtractive What do you get if you mix a bunch of paint?

39. Additive vs. Subtractive What do you get if you mix a bunch of paint?

40. Additive vs. Subtractive

41. Additive mixing is most intuitive: ADD wavelengths: red+green = yellow red+blue = magenta blue+green = cyan red+green+blue=white

42. 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…

43. Example: blue + yellow = green Technically it’s called “cyan”

44. The result of a mixture depends on what wavelengths don’t get absorbed by the two pigments wavelength Amount of reflection blue greenyellowred

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

46. Subtractive mixing is commonly used in color printers

47. Everything you’ve learned so far is wrong.

48. Well, not really wrong, just far from complete.

49. What color is this box?