CSC151.01 2014F, Class 14: Transforming Colors
==============================================

_Overview_

* Preliminaries.
    * Admin.
    * Upcoming Work.
    * Extra Credit.
    * Administrative Questions.
    * Exam Questions.
* About the Reading.
* Lab.

Preliminaries
-------------

### Admin

* 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.)

### Upcoming Work

* Lab writeup: Exercises 5e and 7b: <http://bit.ly/151-2014F-w14>
* [Exam 1](../assignments/exam.01.html) due Tuesday night.
    * Bring printed copies on Wednesday.
* Reading for Tuesday:
    * [Transforming Images](../readings/transforming-images-reading.html)

### Warnings on Today's Lab

* 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.

### Extra Credit Opportunities

#### Academic

* Convocation Wednesday: Tara Zahra on Emigration from Eastern Europe
* CS Extras Thursday at 4:30: Mathematical Image Synthesis Toolkit
* CS Table Friday at noon: ???
* Campus Town Hall September 30

#### Peer Support

* Noteworthy, Sat., Sept. 27, 3:30 p.m. Herrick
* Science poster session, Sat., Sept. 27, morningish, science elbow
* Football Games (Saturday, Sept. 27, at 1pm)
* Men's Tennis (???)
* Women's Tennis (???)
* Noteworthy, Sat., Sept 27, 3:30 p.m. Herrick
* Anna Christie, Oct. 9-12 (SB plays Marthy)
* Evan's radio show 5pm Friday nights on KDIC
* Donna's radio show Sunday midnight on KDIC

#### Miscellaneous

* 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.

### Administrative Questions

### Exam Questions

* 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)`

Prepare for Lab
---------------

* 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.