Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
  • Talk about quiz.
• A bit about design.
• A bit about color theory.
• Exploring some images and design spaces.

Preliminaries

Admin

• New partners!
• Mentor session Monday (tonight) at 7:00 p.m.
• Work returned (I hope): Quiz 3.

Upcoming Work

• Exam 1.
  • Exam due in electronic form due Tuesday at 10:30 p.m. (free extension until Wednesday at 10:30 p.m.).
  • Exam due in printed form Wednesday (free extension until Thursday at review time).
  • Required epilogue due Wednesday at 10:30 p.m. (free extension until Wednesday at 11:00 p.m.)
• No lab writeup for today!
• Today will be more of a discussion day. That means we have time for questions on the exam and more at the beginning.
• Reading for Tuesday
  • Raster Graphics: Images from Pixels and Colors
  • RGB Colors

Extra Credit Opportunities

Academic

• Education Film, Wednesday night
• TEDx Grinnell, February 21

Miscellaneous

• Read and comment on the new Grinnell College Guide to Preventing, Reporting, and Responding to Sexual Harassment and Sexual Misconduct. Angela Voos says that she would really like to know what kinds of things might go in an FAQ or instructional video about the reporting process.

Peer Support (Morning Section)

• Julia's radio show, "The Hot Box". Wednesday night/Thursday morning 1:00-2:00 a.m. Favorite songs from musicals.
• Swimming, Conference Championships, February 13-15, The Osgood
• Emma's play, if you can get a ticket. (Information is forthcoming.)

Recommended, But no EC

• 2 <3 GC day on Wednesday.

Questions

What's the difference between a drawing and an image?

A drawing is a conceptual thing; it's a collection of colored ellipses and rectangles. An image, in contrast, is a reference to GIMP's rendering of something visual.

How many test is enough?

Make sure that you cover all the cases, but each test can cover multiple cases. I would guess that ten different tests would suffice.

How many tests should we include?

For the test suite problem (#5), I want to see all of your tests.

For the others, it's still probably nice to see your experiments, but not required.

Do we make our test suite specific to our implementation?

No. Test suites are intended to test any procedure that tries to meet the given requirements/expectations.

About Quiz 3

Problem 1: Find the difference between a number and the square of its square root

    (define error-root-squared
      (lambda (number)
        (- number (square (sqrt number)))))

    (define error-root-squared
      (lambda (x)
        (- x (* (sqrt x) (sqrt x)))))

    (define error-root-squared
      (lambda (val)
        (- val (expt (sqrt val) 2))))

• Remember: The thing you are subtracting from comes on the left.
• We use display rarely.

Problem 2: Given lots of weird code, figure out what it does.

• In describing a drawing, I expect:
  • The shape
  • Width and height
  • Position (left/right,top/bottom) or center
  • Color
  • Or that for each element of a group, if it's a group

First thing

    (define circ
      (hshift-drawing 0.5 (vshift-drawing 0.5 drawing-unit-circle)))

• Procedure or value? It's a value.
• What type of value? It's a drawing.
• What drawing? A circle centered at (0.5,0.5) diameter of 1, color of black Left is 0, top is 0, right is 1, bottom is 1.

Telling the difference between values and procedures

    (define sam 2)
    (define prof-rebel (lambda (x) (- x 10)))

    (define shape
      (lambda (h v)
        (hshift-drawing h
                        (vshift-drawing v
                                        (hscale-drawing h
                                                        (vscale-drawing v
                                                                        circ))))))

• Procedure or value? Procedure
• Inputs: Two positive real numbers
• Output: Drawing. The outermost procedure call is supposed to return a drawing
• Suppose I used 10 for h and 20 for v, what drawing will I get? An ellipse (ellipsoid, oval-like object), height of 20, width of 10, left edge at , top edge at _,
  • Originally, left and top edges of circ were at 0
  • After vertically scaling and horizontally scaling, left edge still at 0, top edge is still at 0.
  • (Center was at (0.5,0.5), multiply by (10,20), center is now at (5,10).)
  • Next we horizontally and vertically shift
  • Width is 10, Height is 20, Left is 10, Top is 20. Black.

Last part

    (define munge!
      (lambda (image)
        (drawing-render! (shape (* 1/3 (image-width image))
                                (* 1/3 (image-height image)))
                         image)))

* Procedure or value? Procedure * Parameters/inputs, image * Produces/output * Suppose I give it an image (say the 640x400 image we have on the screen). What's the first thing it does? Computes 1/3 of the width. Computes 1/3 of the height.

• What position will the drawing be at?

A bit about design

A bit about color theory

Exploring some images and design spaces