CSC151 2007S, Class 12: Raster Graphics and RGB Colors

Admin:
* Are there questions on Exam 1?
  * Bring questions!
* Quiz 2 returned.  
  It's clear that many of you had difficulty with mod, 
  so we'll talk about it a bit more.
* EC for attending this Thursday's Thursday Extra.  
  Cable Thompson is speaking about his summer work.
  4:30 in Science 3821.  
* Max's office hours tonight 8-9.  Emily's office hours tomorrow night
  9-10.  THey can't answer test questions, but they can answer question
  like "What *are* the parame3ters to image-render-scaled-spot!?
  (They'll also tell you it is image-scaled-render-spot!)
  (And the 3 is silent)
* I've started to go through assignment 1.  All of you should have received
  responses.  A page of Q&A will appear eventually.
* Today's happy occurence: My spell-checker thinks that 
  "Hanover, New Hampshire" should be "Hangover, New Hampshire"
* Tomorrow we revisit documentation.

Overview:
* Representing images, revisited.
* Pixels and colors: The basics.
* RGB colors.
* Lab.

==Representing Images==

* Two traditional internal representations
  * Raster graphics: An image is a grid, and there is a color at each
    grid point
    * It's a grid of squares, and each square has a color
  * Vector graphics: An image is a collection of drawing primitives
* Two representations are historic
* Our focus right now is raster graphics
* Good internal, but PITN to write programs to generate

==Representing Colors==

* RGB is common on computers
* Often represent each component of the color as a number between 0 and 255
  * 256 possible component values, 16^2 2^8
  * 256*256*256 possible colors
  * Why 256?  Standard measure on the computer