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

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

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

3. Color Vision Perceiving Color • Primary colors RedGreenBlue

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

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

6. Color Vision Perceiving Color • 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

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

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

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

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

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

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

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

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

15. Color Vision Theories of Color Vision: Trichromatic Theory • 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)

16. Color Vision Theories of Color Vision: Trichromatic Theory • 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

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

18. Color Mixing • 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. Color Mixing • 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!

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 Theories of Color Vision: Trichromatic Theory • 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

23. Color Vision Theories of Color Vision: Trichromatic Theory • 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

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

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

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

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

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

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

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

31. Theories of Color Vision: Trichromatic Theory • 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

32. Theories of Color Vision: Opponent-Process Theory • Opponent-Process Theory • color is determined by outputs of two different continuously variable channels: • red - green opponent channel • blue - yellow opponent channel

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

34. Color Vision Wavelength and Color • White light is a mixture of wavelengths • prisms decompose white light into assorted wavelengths • OR recompose a spectrum into white light

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

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

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

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

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

40. Color Mixing • Additive vs. Subtractive WHY?

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

42. Color Mixing • 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. Color Mixing • Example: blue + yellow = green Technically it’s called “cyan”

44. Color Mixing • The result of a mixture depends on what wavelengths don’t get absorbed by the two pigments Amount of reflection green yellow red blue wavelength

45. Color Mixing • Both yellow and blue pigments reflect a bit of green Amount of reflection green yellow red blue wavelength

46. Color Mixing • Subtractive mixing is commonly used in color printers

47. Color is an illusion • Everything you’ve learned so far is wrong.

48. Color is an illusion • Everything you’ve learned so far is wrong. • Well, not really wrong, just far from complete.

49. Color is an illusion • What color is this box?

50. Color is an illusion • What color is this box?