CSC151 2007S, Class 34: Storing Images as Simple Pixel Maps

* I will continue to reserve time at the start of class for a discussion of campus issues.

Admin:
* Preregistration is approaching soon.  
  I hope many of you will think about taking CSC161, the next CS course.
* Coming not-so-soon to a newspaper near you: Column by SamR
* Happy April Fools' Day! (or not).
* Raw eggs in shell break when you freeze them.
  [Farmer, L.A., 2008]

Overview:
* Files, revisited.
* Storing images.
* Storing colors.
* Storing images, revisited.

==A File is ===

* Something stored on your computer
* Provides permanent storage
* We have text files
  * And lots of other kinds of files
* We might want to store images
  * One technique: Store images through code
    * Compact but slow
  * Lots of other techniques that represent the image itself, not the
    process used to create it
    * JPG, PNG, GIF, SVG, TIFF, RAW, BMP, ...

* Over the next week or so: Design our own representation

* What things might we care about as we design a file format for images?
  * Color range supported (e.g., GIF only supports 256 colors)
  * Accuracy (e.g., JPG only approximates the image)
  * File size
  * What additional information does the file hold? (E.g., layers, comments,
    encrypted data as in steganography, ...)
  * Ease of processing (creating, reading back)
  * Human readability
* Responsible design
  * Should you patent your design?  NO
  * Should you copyright your design?  UNAVOIDABLE
  * SHould you add a creative commons license to your design?  YES
  * Should you pbulish your design so that bozos don't patent it?  YES

== Writing Lots of Colors ==

* Use map
(map (lambda (color) (rgb-write color out)) 
     (list color-white color-black color-blue color-green color-yellow))
(map (lambda (color) (rgb-write (cname->rgb color) out)) 
     (list "yellow" "white" "black" "green" "blue" "blue" "black"))