1. Midterm 2 March 9 th and 10 th Review Session Monday 7pm in this room (probably)

2. Color Vision White light is a mixture of wavelengths –prisms decompose white light into assorted wavelengths Wavelength and Color

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

4. Color Vision Primary colors Perceiving Color Red Green Blue

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

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

7. 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

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

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

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

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

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

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

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

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

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

17. 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

18. 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

19. 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

20. 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?

21. Magenta Think about why!

22. 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!) Theories of Color Vision: Trichromatic Theory

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

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

25. 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

26. 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

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

28. 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

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

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

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

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

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

34. Additive vs. Subtractive

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

36. 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…

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

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

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

40. Subtractive mixing is commonly used in color printers

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

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

43. What color is this box?