CSC151.01 2015S, Class 14: Transforming Colors
==============================================

* New partners!

_Overview_

* Preliminaries.
    * Admin.
    * Upcoming Work.
    * Extra Credit.
    * Questions.
* Lab.

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

### Admin

* Mentor session tomorrow at 8:00 p.m.
* Review sessions tomorrow at 9:00 a.m. and 1:15 p.m.
* No quiz Friday!
* Using the virtual machine requires that you read the instructions.
* Three parts to every question.
     * Your code
     * Your command in the interactions pan
     * Error message or description of problem

### Upcoming Work

* [Exam 1](../assignments/exam.01.html).
    * Exam due in electronic form due last night at 10:30 p.m. (free extension
      until tonight at 10:30 p.m.).
    * Exam due in printed form TODAY (free extension until Thursday
      at review time).
    * Required epilogue due TONIGHT at 10:30 p.m. (free extension until
      TONIGHT at 11:00 p.m.)
    * I'll collect printed exams now for those who have finished.  For
      those who haven't, bring them to review session tomorrow or slip
      them under my office door before then.
* No lab writeup for today (no matter what it currently says online)
* Reading for Friday
    * [Boolean Values and Conditionals](../readings/boolean-reading.html)
* HW4 due next Tuesday (to be distributed later tonight): Color and
  Image transformations
    * You will write color transformations, like you are doing in class
      today.
    * You will learn how to apply them to images.
    * Your partner is your lab partner from today's class

### Extra Credit Opportunities

#### Academic 

* TEDx Grinnell, February 21

#### Peer Support (Morning Section)

* Julia's radio show, "The Hot Box".  Wednesday night/Thursday morning 
  1:00-2:00 a.m.  Musicals.  TONIGHT
* Swimming, Conference Championships, February 13-15, The Osgood
* Track and Field, Saturday, February 14, the "We Don't Yet Have a Million Dollar Donor Who Wants to Name a Gym" Field House

### Recommended, But no EC

* 2 <3 GC day next Wednesday.

### Questions

_How should I notate how long each problem took?_

> Something like

        ; Problem 2
        ; 30 minutes

> I've seen students write

        ; Problem 2
        ; Started at 11:10:05, stopped at 11:21:14.  Restarted
        ; at 11:55:01.  Stopped at 11:55:02.  My head hurts.
        ; ..
        ; Total of fifteen minutes and 11.5 seconds.

Lab
---

Debrief
-------

* Since you can't have a component greater than 255 or less than 0, some
  of the transformations are capped and therefore don't work quite as
  you think they should.
* Yes, we are once again in a world in which procedures do not change
  their parameters.  
    * `(irgb-redder mycolor)` does not change `mycolor`.
* Yes, we are once again a world in which the order in which we apply
  procedures can matter.
    * `(irgb-darker (irgb-complement mycolor))` is not the same as
      `(irgb-complement (irgb-darker mycolor))`
* Why use

        (image-set-pixel! image1 0 0
                          (irgb-redder (image-get-pixel! image1 0 0)))

    * Because we don't need to use the same image or position

        (image-set-pixel! image1 0 0
                          (irgb-redder (image-get-pixel! image2 0 0)))

        (image-set-pixel! image1 2 3
                          (irgb-redder (image-get-pixel! image1 3 2)))