Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Main Concepts
  • Representing images, revisited.
  • Pixels and colors: The basics.
  • RGB colors.
  • Those weird numbers.
• Setup
• Lab

Preliminaries

Admin

• New lab partners today.
• Cookies!
• HW 2 returned soon.
• Review sessions tonight, Thursday at 10 am, and Thursday night.
• I've rearranged the schedule of topics slightly to give us time to talk about testing on Friday.
  • The two sections will be out of synch for the next week or two.

Notes from Epilogues on HW 3

• Not all of you filled in the epilogues. Please take the time to do so. Evidence suggests that you learn better if you bookend your assignments: Think about the work in advance, do the work, reflect on it.
  • This approach can also help with more general skills, such as reading tasks and assessing workload.
• There was a huge range of time spent, from 3 to 9 hours.
  • The 9-hour group noted that they needed to ask for help earlier.
  • Other long groups noted that they needed to ask for help earlier.
  • Still others just noted that there were a lot of hard problems on the assignment. We thought of 2 as hard, but mostly variants of the same hard problem.
• A variety of notes about group work
  • Working with others makes it more efficient.
  • Scheduling is hard.
  • What should I do when my partner seems to understand it better than I do?
    • Ask partner to slow down and explain.
    • Let them zoom ahead and then ask them to explain. (Sam thinks early questions are better.)
    • Let them zoom ahead and then do it on your own. (Not a good use of time.)
    • Ask them to stop and let you try to explain it to them, or at least work through an example.
  • What should I do when I have an idea, but I can't convey it to my partner?
    • Ask them to explain their thought process.
    • Work through an example with them.
    • Where are you confused?
  • What should we do when we each want to try a different approach to a problem?
    • Talk them out a bit
    • It's worth presenting all of them and choosing criteria for choosing
    • When you form your group, appoint a director. He/she/zi chooses
• Other important lessons
  • DrRacket likes to crash. Save early and often.
  • It can be difficult to communicate an approach to your colleagues.

Upcoming Work

• Lab Writeup: Exercise 10 <151-2014F-w12>, due Friday.
• Exam 1 distributed. Due next Tuesday evening.
  • We will go over the policies today
  • We will go over the problems on Friday (and Thursday, if you'd like).
• Study for Friday's quiz.
  • Friday's quiz: Drawings, Side effects, Documentation, Procedures
• No readings for Friday. (You may want to revisit the reading on testing.)

Campus Events of Interest

• Rosenfield seminar on Scotland, Thursday afternoon/evening.
• Rebecca Hamlin book talk today at 4:15 pm.
• Internship talks Wednesday and Thursday afternoons.

Extra Credit Opportunities

Academic

• Convocation TODAY: President Kington
• CS Table Friday: Browser Tracking
• Campus Town Hall September 30

Peer Support

• Football Games (???)
• Men's Tennis (???)
• Women's Tennis (???)
• Anna Christie, Oct. 9-12 (SB plays Marthy)

Miscellaneous

• 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.

Administrative Questions

Setup

• Spend two minutes talking to your partner about the readings.
• Post any questions to the class questions form .
• I'll look at the questions and do my best to answer.

How do you specify a 9x5 image?

(define nine-by-five (image-new 9 5))
(define landscape (image-new 9 5))
(define canvas (image-new 9 5))
(image-show nine-by-five)

What is the "i" in "irgb"?

• "Integer". These are "integer encoded RGB colors"

What's the difference between an image and a drawing?

• In our world, a drawing is a composition of scaled and shifted and recolored unit circles and unit squares.
• An image is a representation of a picture. Images are basically grids of pixels.

In procedure names, is there a difference between "rgb" and "irgb"?

• No. We are sometimes not good at updating our instructions to match updates in our concepts. Both work.

Lab