CSC151 2010S, Class 10: Raster Graphics and RGB Colors

Overview:
* Representing images, revisited.
* Questions on the Readings?
* Those weird numbers.
* Lab.

Admin:
* Reading for tomorrow: Transforming RGB Colors.
* Reminder: If you're going to miss class (or if you missed class), 
  please send me a note at the earliest possible time.
* Due to popular request, I will be shifting the time of quizzes.  
  How does Mondays sound?
* Due to the weather, our schedule has shifted a bit.  
  We hope to have Prof. Kluber visit on Friday.
* Are there questions on Assignment 3?
  * Should we prioritize short or general
    SHORT!
    But correct: A drawing is scalable and shiftable
    Hint: An 8x8 checkerboard is a good starting place
* EC for Thurday's convocation.
* EC for today's Health Fair.
* It's new partner day!

Drawings
* Represented as a grid of colors (Raster graphics)
* We also need ways to talk about colors
  * Easy computer standard: RGB
  * We look at each color as a combination of
    red, green, and blue
    * We use the simple range 0..255
      256 values: easy to represent with a
      "byte", the standard unit of storage
      on most modern computers

* To work with these types, we need procedures
  (image-set-pixel! image x y color)
     sets a pixel in an image
  (image-get-pixel image x y)
  (rgb-new red green blue)
    -- (context-set-fgcolor! (rgb-new 128 0 255))
  (rgb-red color)
  (rgb-green color)
  (rgb-blue color)