Announcements 4/9/12 Prayer HW 25 due on Tuesday HW 26 due on Wednesday (but it’s very likely Claira won’t pick it up until Thursday night. Shhh!) Frank & Ernest

Reading Quiz How many types of cone cells are there in humans? a. a.1 b. b.2 c. c.3 d. d.4 e. e.5

Reading Quiz The functions r( ), g( ), and b( ) are called the: a. a.color adding functions b. b.color displaying functions c. c.color matching functions d. d.color realizing e. e.color subtracting functions

The Goal

Visible Spectrum “All the colors of the rainbow…”  Where is brown?? What’s a “luminescence spectrum” that you might measure? From Wikipedia, “Visible Spectrum”

Cone cells “Short” “Medium” “Long” From Wikipedia, “Color Vision”

Color blindness tritanomaly – S cones mutated (rare) tritanopia – lacks S cones (<1% of males) deuteranopia – lacks M cones (1% of males) deuteranomaly – M cones mutated (6% of males; 0.4% of females) protanomaly – L cones mutated (1% of males) protanopia – lacks L cones (don’t know %) From Wikipedia, “Color Blindness” Test for deuteranopia Test for tritanopia

Primary Colors How the primary song should go “Additive color mixing” – demos Subtractive colors - demo From Wikipedia, “RGB Color Model”

Components of R, G, B Plot 3 components in 3D “color space” From Wikipedia, “RGB Color Model”

What are R, G, B? The spectra of R, G, and B phosphors from a standard CRT (i.e. non LCD) computer monitor Could also, e.g., have R = sharp peak at 635 nm, G = sharp peak at 532 nm, B = sharp peak at 447 From Wikipedia, “Primary Color”

A Problem R = sharp 635 nm, G = sharp 532 nm, B = sharp 447 nm What happens if you want to get, say, orange = 580 nm. Can you mix R, G and B to get this?   532 nm will excite some S!   580 nm alone will never excite S!

1920’s Experiments red source = 700 nm green source = nm blue source = nm From Wikipedia, “1931 Color Space” (also in P&W) Important results: 1.Human eye response can (mostly) be described by 3 parameters 2.Human eye response is (mostly) linear to get 580 nm orange, need some “negative” blue

What is a “Color Space”? How strong of r, g, and b, lights would you need to match a light that is not a delta function? Compare: what would you get for the response of a detector that has, say, g-bar as its response curve?

1931 Color Matching Functions From Wikipedia, “CIE 1931 Color Space” Human eye response again Properties of these functions: all are positive z-bar = very close to S cones, very close to previous b-bar y-bar = matches intensity response of eye, very close to M cones x-bar = chosen so that white is equal parts x-bar, y-bar, z-bar

1931 Color Matching Functions etc.

Worked Example X = Y = Z = Normalize (because “color” should not depend on overall intensity) x = y = z =