Overview

• Preliminaries.
  • Admin.
  • Homework.
  • Questions.
• Representing images.
• Thinking about drawings through composition/decomposition.
• The underlying representation.
• Pure approaches vs impure approaches.
• Lab.

Preliminaries

Admin

• Lab partners assigned for the week. (This is a "same sex" week as part of our broader partner preference experiment.)
• We had a family emergency this weekend, so it will take me a few more days to respond to your introductory surveys. (Yours is my largest class, so you folks are last.)
• Study break in the CS commons at 8pm tonight. Home-made (well, probably apartment-made) snacks.
• The TC Corps is hiring! Contact [tranchri] or [cohnhann] for details.
  • Probably other people, too.
• I've graded your first quiz. I'll return it during class, possibly while you are doing lab.
  • No other attendance.
• I've changed my homework grading strategy a bit, to "Excellent, Very Good, Good, Fair, Poor" (it's more or less the same as the old check system, but with new words). Updates to the handouts will follow.
• Note that if you use the "Source" version of an EBoard, you should see the stuff within a minute or two of me updating it.
• I think I've responded to all of the lab writeups I've received.
  • Please send lab writeups to me. Your graders don't need to see them.
• We will continue today's lab tomorrow.
• Extra credit:
  • Thursday at 4:15: Spencer Liberto, Lea Marolt Sonnenschein, and Daniel Torres on Ushahidi and more.
  • CS Table Friday at Noon: The ACM Code of Ethics.
  • Convo Feb. 5. (Ill give my "Why go to convo" lecture closer to the date.)
  • Others?

Homework

• HW 2 is due tomorrow night.
• Reading: Procedures as values
• Today's lab writeup (due Friday): Exercise 4, parts a, c, d, f, and g
  • Email subject: CSC 151 Writeup 3: Drawings as Values (YOUR NAME(s) HERE)
  • You can, but need not, write up the lab with your partner.

Questions on HW 2

Representing images

• Images are the primary problem domain for this class.
• We'll give you a model of what the computer can do
• We'll ask you to write algorithms to make certain kinds of images
• There are LOTS of ways to think about images

Thinking about drawings through composition/decomposition

• New data type!
  • What kinds of values does the data type include?
  • What do I use them for?
  • How do we describe them to the computer?
  • How does the computer describe them to us?
  • What operations can I perform on these values?
• What kinds of values does the data type include?
  • Circles, squares, rectangles, ovals, and combinations thereof
• What do I use them for?
  • To make "interesting" images (or at least images)
  • "As ways of describing images"
• How do we describe them to the computer?
  • drawing-unit-circle (diameter 1, centered at 0,0)
  • drawing-unit-square (side length 1, centered at 0,0)
  • Apply the operations below to other drawings
• How does the computer describe them to us?
  • (drawing circle ? ? left top width height)
  • As pictures, if we use (image-show (drawing->image DRAWING WIDTH HEIGHT))
• What operations can I perform on these values?
  • (scale-drawing AMT DRAWN
  • (hscale-drawing AMT DRAWING)
  • (vscale-drawing AMT DRAWING)
  • (hshift-drawing AMT DRAWING)
  • (vshift-drawing AMT DRAWING)
  • (recolor-drawing NEWCOLOR DRAWING)
  • (drawing-group DRAWING1 DRAWING2)
• Can we group more than two drawings? Yes.
• Is drawing-unit-circle already defined? Yes.

The underlying representation

See above.

Notes from Lab

All of the procedures create a new drawing; they don't modify the original drawing.

The combination of scaling and shifting seems odd. Why?