CSC151.01 2015S, Class 22: Images as Functions from Position to Colors
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* New partners (who will also serve as homework partners)!
    * Separate cards for those who do and do not want a HW partner

_Overview_

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

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

### Admin

* Quiz Friday!  Conditionals, higher-order procedures and let.
* Review sessions Thursday 9:00 a.m., 1:15 p.m., and 8:00 p.m.
* Office hours Today at 10:00 a.m.
    * <http://rebelsky.youcanbook.me>
* Our graders say
    * "Please limit your lines to eighty characters!"
    * "Remember that we are going to copy and paste your work into
      DrRacket.  So don't add things after you copy and paste from
      DrRacket."
* Your peers say   
    * "It's really helpful to save your work from the interactions pane."
    * "Copy-paste-comment"
* I plan to distribute an answer key to HW 5 tonight (or when the last
  homework comes in).

### Upcoming Work

* [Homework 6](../assignments/assignment.06.html).
    * Due Tuesday at 10:30 p.m.
* Exam 2 to be assigned in a week.
* Lab writeup for today: Problem 3
  <http://bit.ly/151-2015S-lab22>
* Reading for Friday
    * [Building Data Structures with Heterogeneous Lists](../readings/heterogeneous-lists-reading.html)

### Extra Credit Opportunities

#### Academic 

* Pioneer Diversity Council Diversity Dialogue, 8:30 p.m. Thursday the 26th, 
  Main Quad "Academic Athletes and Academic Students".  
* CS Table Friday - Art, CS, and Artificial Intelligence.

#### Peer Support (Morning Section)

* Julia's radio show, "The Hot Box".  Wednesday night/Thursday morning 
  1:00-2:00 a.m.  
* Host a prospie.
* Indoor Track this Saturday
* Neverland Players Friday and Saturday at 7:00, Sunday at 1:30 and 7:00.
  Tickets at Bucksbaum.  Get one before they sell out.
* Nobody Gets Hurt, a show with an audience of one.  Info on trying to
  get one of the tickets is on the posters.
* Orchestra in a week and a few days.
* Grinnell Singers Sunday at 2pm.  Handel's Esther.  Maybe Sebring Lewis.

### Other Good Things

* Jazz band Thursday night in Gardner.

### Questions

_Will you add my cool event above?_

> Done.

Lab/Debrief
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How do I generalize my blend?

                Start           Mid             End
        Column  0             width/2           width
        BlaBlu  0                               255
        ??      128                             255
        ??      64                              196

How can I check my pixel values for a blend?

        > (define blend (horiz-black-blue-blend 100 100))
        > (map (lambda (col) (irgb->rgb-list (image-get-pixel blend col 50)))
               (iota 100))

Many of you computed a multiplier using (/ 256 width) (/ 255 width).
Is there a problem with that approach?  (Hint: What if width is 2?)