CSC151.02 2016S, Class 07: Transforming Images

Overview

Preliminaries

Office hours: MTWF 10-11, Tu 1-2.
- Sign up at http://rebelsky.youcanbook.me.
- Also feel free to stop by when my door is open.
- Or to email me for an appointment.
Tutor hours
- Sunday, 3-5 p.m.
- Sunday-Thursday, 7-10 p.m.
Weekly review sessions:
- Wednesday at 8pm in the CS Commons with Sarah
- Thursday at 10am in this room with SamR
- Thursday at 8pm in the CS Commons with Kumar

Quiz Friday
- Topics
  - Scheme's order of evaluation and sequencing.
  - Definitions (in Scheme).
  - Arithmetic operations, including things like max, min, floor, ceiling, round, quotient, and remainder.
  - RGB colors, and the operations on integer-encoded RGB colors.
  - Basic RGB transforms (although we will remind you of what they do): irgb-redder, irgb-greener, irgb-bluer, irgb-darker, irgb-lighter, irgb-complement, irgb-rotate, irgb->string
  - Function composition.
- Form
  - Closed book
  - Possibly: "evaluate this expression (or series of expressions)"
  - Possibly: "using composition, write a procedure to compute ..."
  - Possibly: "given this definition, what does this procedure do?"
Readings for Friday:
- Writing Your Own Procedures
- How Scheme Evaluates Expressions (v2)
Assignment 3 due next Tuesday at 10:30 p.m. (Your assignment partner is your partner from today.)
Lab Writeup: Exercise _
- Send email titled CSC 151 Lab Writeup _ (Your Names)
- Do not include the underscores.
- Send to CSC151-02-grader@grinnell.edu
- Due before class on Monday.

If you know of other events, please suggest them! (I might not always agree, but it never hurts to ask.)

Send email to rebelsky@grinnell.edu with a subject of "CSC 151 Extra Credit (Your Name)"

I try to respond within a week. You'll have a report of grades by next Monday.

4 pm Thursday in this room: LaTeX
4 pm Thursday in JRC 209 - Funding for unfunded internships
Next week's Rosenfield Symposium on Campaign Finance Reform.
noon Tuesday in the White PDR: Bowie, Mickey, and more: Copyright in the 21st century (copies of the reading outside Sam's office)
7:30 pm next Tuesday in ARH 131 - Funding for unfunded internships

Social Dance Workshop Tuesdays 7:00-8:00 in Bucksbaum Dance Studio (starting next week)
Pun club Saturdays at 4pm in Younker (max 2)
Socrates Cafe' Saturdays (max 2)
Electrronic Potpourri on KDIC Frridays at Five

Why do you have so many web pages?

To clarify or confuse or both

Why so many links at the top of each page?

Once you're used to it it speeds navigation.

What are the important topics from yesterday's class and today's class?

Monday

Colors are represented in Scheme as combinations of red, green, and blue which are put together into a single integer that most of us can't read.
- (by multiplying the red component by 256*256, multiplying the green component by 256, and then adding the three values together.)
We can preview colors with things like (image-show (color-palette ...))
When you nest operations, you get things in one neat line and the work is done inside-out

Yesterday

Colors can be transformed by complementing the components (the pseudocomplement of a color, when added to a color, gives you 255 for each); enhancing the red, green, or blue component; and more.
We can make colors lighter by increasing all three components.
We can build new functions by composing other functions. If we write (define irgb-evan (o irgb-complement irgb-bluer irgb-complement)) irgb-evan makes a color less blue.

Today

You can load images and play with them by applying a color transformation to all of the pixels, using image-variant.
We have this magic thing called sectioning that builds functions from other functions by filling in some of the parameters to the procedure.
For example, we can eliminate red, green, or blue components
For example, if we write (define st (section expt <> 3)), st ...

Lab writeup: