CSC151 2007S, Class 06: Transforming Colors

Admin:
* No reading for Monday!
* Reminder: EC: Cross-Country meet this weekend. (Oakland Acres; Buses depart from PEC)
* EC: Math video at noon on Monday.  Free pizza! (3821)
* Please don't ask for extensions at 2:00 a.m.
* From now on, I am making the due time for assignments 4:00 p.m.
* HW4 assigned.
* Note: Poor proofreading in the lab
  "pixel-map" should be "image.map"
  "pixel-map!" should be "image.map!"

Overview:
* Preliminary lessons from HW3.
* Key points from the reading.
* Questions and answers.
* Lab!

/Preliminary Lessons from HW3/
* Let Scheme figure out the values; you don't have to.
  * Problem: Copy the color in (0,0) from src to (0,0) in destination
	> (define tmp (image.get-pixel src 0 0))
	> (rgb->string tmp)
	"127/32/90"
	> (image.set-pixel! destination 0 0 (rgb.new 127 32 90)
  * Alternate:
	> (define tmp (image.get-pixel src 0 0))
	> (image.set-pixel! destination 0 0 tmp)
  * Alternate
	> (image.set-pixel! destination 0 0 (image.get-pixel src 0 0))
* Not a new issue: "Set pixel 1 1 to purple"
  > (cname->rgb "purple")
  -1442775041
  > (image.set-pixel canvas 1 1 -1442775041)
  VS
  > (define purple (cname->rgb "purple"))
  > (image.set-pixel canvas 1 1 purple)
  VS
  > (image.set-pixel canvas 1 1 (cname->rgb "purple"))
* Definitions window vs. Interactions window.
  * When you hit "run", everything in the interactions window disappera
  * WHen you hit "run", any call to image.new or image.load creates a new
    image, WHICH IS DIFFERENT THAN THE ONE YOU CURRENTLY SEE ON THE SCREEN
* Some problems not even Emily can fix.
* Computers are Sentient and Malicious.
* More on Tuesday.

/Key Points from the Reading/

* Topic: Thinking about transforming colors
* Scaling: Once you know how to transform a color, you can transform a 
  pixel or even a whole image
* Controlling operations:
  * In Scheme, "map" means "compute with every component"
  * IN Math and Scheme, "compose" means "do two things in sequence"
/Questions and Answers/

/Lab + Reflection/

* Don't work with huge images, at least not now
* REMEMBER! Every lab is online.  WHen there's a lot of code to type, copy/paste!
* How far did you get in the lab?
  * No further than Problem 3 
  * Beyond Problem 3 but no further than Problem 6
  * Beyond Problem 6 but no further than Problem 9