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. 1b. 2c. 3d. 4e. 5

Reading Quiz The functions r(), g(), and b() are

called the:a. color adding functionsb. color displaying functionsc. color matching functionsd. color realizinge. 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 deuteranopiaTest 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 Experimentsred source = 700 nm green source = 546.1 nm blue source = 435.8 nm

From Wikipedia, “1931 Color Space” (also in P&W)

Important results: 1. Human eye response can (mostly)

be described by 3 parameters2. 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

( ) ( )X I x d ( ) ( )R I r d etc. etc.

Worked Example

X = Y = Z =

Normalize (because “color” should not depend on overall intensity) x = y = z =