CSC 151.01, Class 14: Pause for breath

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Questions
• A bit more on testing
• Representing images
• Reminder: types
• Lab

News / Etc.

• Continue partners.
• Happy valentine’s day! I brought you treats.
• We start a new model of images today. Yay!
• Don’t ask about new extra credit events ten minutes before they start.

Reminders

• Use our tutors! We have tutors available Sunday through Thursday evening from 7-10 p.m. in Science 3813/15.
• Ask questions via email! I’m always happy to (try to) answer questions via email. There is no need to apologize when sending me questions. If I take too long to answer, send another email (or even text, if it’s a reasonable hour).
• Visit me in my office! I’m always happy to see students during my office hours. I prefer that you book me at https://rebelsky.youcanbook.me, but you can also just show up during office hours and hope that I’m not busy.
• Visit mentor sessions! We have mentor sessions on Wednesday and Thursday evenings from 8:00-9:00 p.m. in the CS Commons. Wednesdays will be more Q&A, Thursdays will include sample quizzes.
• Visit review sessions! I run review sessions on Thursdays at 9am in this room.
• We have individual tutors!
  We have individual tutors available for those who take advantage of the above and find that it’s not enough.
• Visit our store! We have office supplies in the commons. Price is free will donation.
• Get news! Feel free to ask me to sign you up for the department mailing list.
• Suggest extra credit! Send me extra credit ideas and opportunities.

Upcoming Work

• Exam 1 due TONIGHT at 10:30 p.m.
  • If you’ve been using images in your directory for experiments, note that those paths make your exam identifiable. Make sure to change the image path to "/home/rebelsky/Desktop/kitten.jpg" or "/home/rebelsky/Desktop/kington.jpg".
• Epilogue due Wednesday at 10:30 p.m. (but do it immediately after the exam anyway)
• Lab writeup, problem ?, due Friday before class.
• Reading: Making and manipulating homogeneous lists due tomorrow.

Extra credit (Academic/Artistic)

• CS Table, Tuesday at noon, 14 Feb 2017. On Technology, Slots, and Whales. Reading packets should be available outside Curtsinger’s office or Orsera’s office.
• Thursday extras, Thursday, 16 Feb 2017, 4:15 p.m., Science 3821: 4-1 joint BA/MSC program with UIowa.

Extra credit (Peer)

• Friday-Saturday-Sunday, 17th-19th, Swimming and diving conference championships. (You can only get credit for two of the three days; staying for an hour counts.)
• Saturday the 18th, Symphony Concert. 2-4 p.m. Sound painting and more! In Sebring-Lewis.
• NEW Art house print making and cookie decorating event. Saturday February 18th, 1-3PM on JRC 227. Gluten-free options!

Good things to do

• Women’s basketball (Senior day) next Saturday at 1pm.
• Men’s basketball (Senior day) next Saturday at 3pm.
• NEW Slavic coffee house, Saturday, 5:30-7:00 p.m. Bucksbaum Rotunda.

Questions

If mediascript does not show under Gimp, what do I do?

Email Sam with the name of the computer.

Try another computer.

Why do I see #<procedure:>>?

Because you have > somewhere in the definitions pane.

How should I show examples?

Put them in the 000000.rkt file, commented out with semicolons.

Do not comment out with boxes.

What about when we’re manipulating images?

; (image-show (image-increase-contrast (image-load “/home/rebelsky/Desktop/mentor.jpg” 22))

; 5

; ; Yup, looks good to me.

What do you preferred questions look like?

Sam, I’m trying to do this. Here’s what I’ve come up with. Here’s what I understand to be the problem. Here’s a case it doesn’t work. Help!

How much is enough whitespace?

So that it’s readable. It takes some practice to get it right. But make sure that the reader can mostly see what procedures are being applied to what parameters.

How late can we email you?

As let as you want. I may stop responding at 5:30.

A bit more on testing

In yesterday’s class, we wrote the following documentation. (I’ve changed the name of the procedure and added a stub implementation.)

;;; Procedure:
;;;   irgb-brighter
;;; Parameters:
;;;   color, an integer-encoded RGB color
;;; Purpose:
;;;   Compute a lighter version of that color
;;; Produces:
;;;   brighter, an integer-encoded RGB color
;;; Preconditions:
;;;   [No additional]
;;; Postconditions:
;;;   The components are larger than in the original color,
;;;     unless they were already 255.
;;;   (irgb-red brighter) > (irgb-red original)
;;;   (irgb-green brighter) > (irgb-green original)
;;;   (irgb-blue brighter) > (irgb-blue original)
(define irgb-brighter
  (lambda (color)
    color))

Are there alternative postconditions you might write?

• Maybe make more specific.
• Advantages of general vs. specific?
  • If it’s clear that only a few cases are acceptable, specific makes sense
  • If it’s hard to write all of the conditions, specific may be a pain in the neck
  • Sometimes you can’t know specific things, so general postconditions are helpful
  • Sometimes you don’t want to limit the implementation, so general postconditions can be good.
• Perhaps we can decrease some and increase the others. E.g., (irgb 20 100 20) to (irgb 15 200 15).
• We might say that brighter is brighter than original if the sum of the components in brighter is greater than the sum of the components in original.
• If the luma of brighter is greater than the luma of original.

What are some tests you would write?

• Make sure the red component of the result is bigger than the red component of original.
• Make sure the green component of the result is bigger than the green component of original.
• Make sure the blue component of the result is bigger than the blue component of original.
• (check > (irgb-red (irgb-brighter color)) (irgb-red color)))
• (check > (irgb-red (irgb-brighter (irgb 10 10 10))) (irgb-red (irgb 10 10 10))))
• One with a dark component, a bright component, and an intermediate component
• (check > (irgb-red (irgb-brighter (irgb 5 254 128))) (irgb-red (irgb 5 254 128))))
• Check all 0’s. Edge cases are important.
• (check > (irgb-red (irgb-brighter (irgb 0 0 0))) (irgb-red (irgb 0 0 0))))

Morals

• You need to use actual data for tests, you can’t just say “the result is …”
• You need to think about a variety of cases.
• Keep your tests DRY (don’t repeat yourself), if possible. Write a general procedure that you can then apply to specific values.

#lang racket
(require gigls/unsafe)
(require rackunit)
(require rackunit/text-ui)

;> (irgb->string (irgb-darker (irgb 12 123 5000)))
;"0/107/239"
;;; Procedure:
;;;   irgb-brighter
;;; Parameters:
;;;   color, an integer-encoded RGB color
;;; Purpose:
;;;   Compute a lighter version of that color
;;; Produces:
;;;   brighter, an integer-encoded RGB color
;;; Preconditions:
;;;   [No additional]
;;; Postconditions:
;;;   The components are larger than in the original color,
;;;     unless they were already 255.
;;;   (irgb-red brighter) > (irgb-red original)
;;;   (irgb-green brighter) > (irgb-green original)
;;;   (irgb-blue brighter) > (irgb-blue original)
(define irgb-brighter
  (lambda (color)
    (irgb (* 1.5 (irgb-red color))
          (* 1.5 (irgb-green color))
          (* 1.5 (irgb-blue color)))))


(define check-brighter
  (lambda (color)
    (check > (irgb-red (irgb-brighter color)) (irgb-red color)
           (irgb->string color))
    (check > (irgb-green (irgb-brighter color)) (irgb-green color)
           (irgb->string color))
    (check > (irgb-blue (irgb-brighter color)) (irgb-blue color)
           (irgb->string color))))

;(check > 
;       (irgb-red (irgb-brighter (irgb 10 10 10))) 
;       (irgb-red (irgb 10 10 10)))

(check-brighter (irgb 10 10 10))
(check-brighter (irgb 5 254 128))
(check-brighter (irgb 0 0 0))

Representing images

• Throughout the semester, we will look at different models of describing images.
• So far: Grid of pixels that we can transform.
• Today (through Friday): Manipulating some very basic shapes (circles and squares).
• Near future: Describe images through gimp instructions
• Additional: Back to pixels, but how to compute each pixel from scratch
• (Simulated) robotic turtles

Reminder: types

We have a new type: The shape (aka “drawing as values”)

• What can I do with these values? What’s the purpose of having this type?
  • Make simplistic pictures.
• How do we express these values?
  • drawing-unit-circle
  • drawing-unit-square
  • Apply operations to those
• What operations are available to us?
  • (drawing-scale drawing amt) -> Creates a scaled version of the drawing
  • (image-show (drawing->image drawing width height))
• How does Scheme represent these values?

Example

> (image-show (drawing->image (drawing-scale drawing-unit-circle 100)
                              200 200))
2

We see a picture of a radius 50 circle, centered at (0,0).

Lab

We will do this on Wednesday.