CSC151 2007S, Class 35: More Efficient Pixel Maps

* Start-of-class time for discussion of campus topics continues.

Admin:

* Our goal today is to finish Wednesday's lab and to start on a followup lab.
* No additional reading for Monday
  We will continue working on the second lab on Monday.
* Assignment 8 is now ready.  
  We'll talk about it during the introduction to today's material.
* Quiz!

Overview:
* Review.
* Storing data more efficiently.
  * Strategy one: Smaller colors (lab today and Monday)
  * Strategy two: Group pixels (homework)
* Tradeoffs.
* Labs.

=Review=

* How do you store an image in a file
* Strategy: Pixel maps
  Mapping pixels onto an image using a file with the following format
  The file contains a sequence of RGB colors
* The file is currently in human-readable format
  * One strategy: Red, Green, and Blue components
* Traditionally, we write the colors back into the image starting at the
  top-left and going left-to-right, top-to-bottom, row at a time

=How do you write less per image==

* Find shorthand for repeated colors: Homework
* Represent each component of a color with a character
  * How?  How do we convert 127/63/11 to ___
    use integer->char on each component
  * Why?  Only three characters per components