CSC151.01 2014F, Class 14: Transforming Colors

Overview

Preliminaries

New lab partners!
Announcement about the new Peer Advisors in CS program (PACS).
- For people who are interested in CS.
- For people who just want some support.
- For people who just want to hear about what's going on in the dept.
- And there will be food!
- Email zuckerha17@grinnell.edu for more info.
Quiz 3 returned.
I think all of you saw my email about office hours. I'll be in as much as I can today to answer questions on the exam or to talk about difficulties (or both).
A weird problem has cropped up on the test suite for problem 4. I'm working on fixing it.
"When do we have the final?"
- From the home page: The final examination for this course is optional. It can be used as a makeup for one examination. I will count the final examination only if it is higher than your lowest examination, and it will replace the grade for that examination. Our final examination is scheduled for 9:00 a.m. on Friday, Dec. 19. However, since my other course has a final at 9:00 a.m. on Tuesday, December 16, I can also offer the final then. (If neither time works for you, let's talk. I'll find another time.)

In some instances, it may be difficult for some folks' eyes eyes to distinguish certain colors. You may have to look at actual pixel values to see the difference.
Sometimes Gimp doesn't like to show changes to an image. We haven't figured a way around that, other than clicking on the image (not just the window). Grab a mentor if you're having trouble seeing an image.

Participate in #GrinWell.
Friends of Drake Library needs help setting up for their annual booksale on Thursday, October 2 (conveniently, the same night as Grinnell High School's homecoming parade). You can help a good cause and probably get a few free books, too.

How well should we test the procedure?
- Well enough that you can be confident that I can't sneak a non-working procedure by your tests.
Test suite that Sam wrote?
- Wasn't broken. Confusion about use.
- Use: (run-tests suite-scale-drawing-centered)
- Note: The order of parameters to scale-drawing-centered is (scale-drawing-centered scale drawing)

Talk to your partner.
- What did you see as the main points in the reading? (Be prepared to answer.)
- What, if anything, was confusing about the reading? (Feel free to post to the question board.)
Warning! Our computers will be slow for the next few minutes. (I'm not sure why.)
What does bound do?
- Given a value and a lower and upper bound
  - If value is between bounds, returns the value
  - If value is lower than lower bound, returns the lower bound
  - If value is greater than upper bound, returns the upper bound
Why does irgb-phaseshift produce a pseudo-complement?
- "Complement" is a bit vague.
- Since there are 256 possible values for red, green, and blue componet, the one 128 away from a component is a kind of complement.
You are using procedures as parameters. Have we seen it? Where else will we see it?
- New concept!
- Really important; introduced in this reading.
- Will be used almost every day for the rest of the semester.
- Note: When you are sending a procedure as a parameter, DON'T put the open paren in front.
What is phase-shift and how is it used?
- Add/subtract 128 from each componet.
- Used for weird effects.
What's the difference between image-get-pixel! and image-get-pixel
- The first should not exist.