Midterm 2

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

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

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

4. Color Vision Perceiving Color • Primary colors RedGreenBlue

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

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

7. 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

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 Signal to Brain Wavelength Input Cone “Blue” Blue “Green” “Red”

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

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

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

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

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

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

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

17. 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

18. 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)

19. 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

20. 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?

21. 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!

22. Color Vision Theories of Color Vision: Trichromatic Theory • 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!)

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

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

25. 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

26. 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

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

28. 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

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

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

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

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

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

34. Color Mixing • Additive vs. Subtractive WHY?

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

36. 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…

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

38. 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

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

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

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

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

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

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