1. Any questions about the current assignment? (I’ll do my best to help!)

2. Depth This Week: Color & Images Next Week: Depth (Kevin Ponto) Image Compositing (Perry Kivolowitz)

6. This Week Optics & Physics of Color Color in Displays How graphics people talk about color Image Compression & Color Profiles Misc (time permitting)

7. This Week Optics & Physics of Color Color in Displays How graphics people talk about color Image Compression & Color Profiles Misc (time permitting)

8. Please ask questions if you have them!!!

9. What is Color?

10. “Color consists of the characteristics of light other than spatial and temporal inhomogeneities; light being that aspect of radiant energy of which a human observer is aware through the visual sensations which arise from the stimulation of the eye.” --OSA Committee on Colorimetry What is Color?

11. Both a physical quantity of light A wavelength and a visual sensation. A perception

12. What is Color? Both a physical quantity of light A wavelength and a visual sensation. A perception

13. Color as a wavelength Light Source

14. Color as a wavelength Light Source Light

15. Color as a wavelength Light Source Light is composed of photons

16. Color as a wavelength Light Source Photons have specific wavelengths

17. Electromagnetic Spectrum: All wavelengths of light Visible Light (390-700nm): Light we can see (colors) Sun emits entire spectrum

18. Visible Light Short Wavelength Higher Energy Long Wavelength Lower Energy White= All Visible Wavelengths Black= No Visible Wavelengths

19. What is Color? Both a physical quantity of light A wavelength and a visual sensation. A perception

20. Vision is measuring visible light Short Wavelength Higher Energy Long Wavelength Lower Energy

21. Vision is measuring visible light

22. Retina is a bunch of sensors Rods Cones

23. Rods: Shades of grey Sensitive to low-light Densest in the periphery Cones: Responsible for color vision Long (L), Medium (M), Short (S) Densest in the fovea (center)

25. No blue cones Cone Distribution From M. Fairchild

26. Measuring Visible Light Short Wavelength Higher Energy Long Wavelength Lower Energy S M Rod L

27. Trichromacy Color perception is a function of the relative stimulation of the three cone types (L, M, & S) In graphics, this is Red, Green, & Blue!

28. L Cones S Cones Normal

29. This Week Optics & Physics of Color Color in Displays How graphics people talk about color Color Spaces Image Compression & Color Profiles Misc (time permitting)

30. Blue Red Green “Cube” based on three primary colors What (most) monitors use Attempt to stimulate each cone in isolation Computer Graphics: RGB

33. Monitors RGB LCDCRT From M. Stone

34. CRT Monitor

35. LCD Monitor

36. Two properties of monitors define what colors they produce Gamma maps intensity of light emitted Gamut maps the space of possible colors generated by a display

37. The amount of light emitted from a monitor is nonlinear pixels intensity

38. Gamma parameter makes light intensity linear

39. Original Small Gamma Large Gamma

40. Gamuts Visible colors (grey) versus colors supported by the display (triangle) Gamut: Colors that can be created using the three display primaries

41. Gamut Mapping Moving an image from one devices’ gamut to another

42. How could you do gamut mapping when moving to a smaller gamut (e.g. less available colors)?

43. Clip colors outside of the new gamut Center the new colors with the old and then clip Scale everything down towards the middle of the gamut Scale just the primaries down towards the gamut Original

44. This Week Optics & Physics of Color Color in Displays How graphics people talk about color Image Compression & Color Profiles Misc (time permitting)

45. Who talks about color? Graphics people Physicists Psychologists Artists & Designers

46. Physicists Short Wavelength Higher Energy Long Wavelength Lower Energy

47. Physicists: Spectral Distribution From Stone’s A Field Guide to Digital Color

48. Blue Red Green “Cube” based on three primary colors What (most) monitors use Attempt to stimulate each cone in isolation Computer Graphics: RGB

49. Why might choosing primaries that target cones (L, M, S) not work?

50. Different cones respond to the same wavelengths M L

51. M L

52. Metamerism Colors with different spectral distributions appear the same From Stone’s A Field Guide to Digital Color

53. Different cones respond to the same wavelengths M L

54. How could we fix this?

55. Negative light would need to shut down responses from a particular cone M L Imaginary Primaries!

56. Negative light isn’t a thing… Hence, imaginary Instead, psychologists look at how the brain interprets color

57. An aside: aspects of color Luminance: How light something is Saturation: How colorful something is Hue: What color something is

58. Psychologists: CIE XYZ Intended to reflect perceptions based on cone primaries Y: Lightness XZ: Hue/saturation plane From Stone’s A Field Guide to Digital Color

59. Opponent Color From M. Stone

60. CIELAB L: Lightness AB: Hue/saturation plane based on opponent responses Euclidean distance is meaningful!

61. CIELCh (Polar LAB) Lightness Hue Colorfulness Unique black and white Uniform differences Perception & design From M. Stone

62. Psychologists’ way of talking about color is perceptually accurate, but difficult to understand & implement.

63. Artists Think in terms of lightness/hue/saturation Munsell Look-up Tables From Gretag-Macbeth

64. HSV/HSL

65. Color Blending Physical Pigments CMYK Monitors & Light

66. Thursday Optics & Physics of Color Color in Displays How graphics people talk about color Image Compression & Color Profiles Misc (time permitting)