CSC151.01 2014F, Class 12: Raster Graphics and RGB Colors
=========================================================

_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](../assignments/exam.01.html) 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 <bit.ly/151questions>.
* 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
---