Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Models of images.
• Iterating over positions: Images as functions from position to color.
• Blends and other positionally-computed images.
• Drawing simple shapes.
• Some strange computations.

Preliminaries

Admin

• Thanks to JS the Elder for the notes!
• Continue partners!
• Prof. Curtsinger will be teaching class for the rest of the week.
  • If anyone wants to take notes for eboards, I'll provide extra credit.

Reminders

• No more office hours this week.
  • I'll do a lot of email or text Q&A this week.
• Tutor hours
  • Sunday, 3-5 p.m.
  • Sunday-Thursday, 7-10 p.m.
• Weekly review sessions:
  • Wednesday at 8pm in the CS Commons with
  • No Thursday review session this week .... )-:
  • Thursday at 8pm in the CS Commons with

Upcoming Work:

• Reading for Tuesday
  • Building Data Structures with Heterogenous Lists
• Assignment 5 due TONIGHT at 10:30 p.m.
• Exam 2 to be distributed on Wednsday.
• Lab Writeup: Exercise 3
  • Send email titled CSC 151 Lab Writeup 22 (Your Names)
  • Do not include the underscores.
  • Send to CSC151-02-grader@grinnell.edu
  • Due before class on Friday.

Extra Credit

• Send your reports to rebelsky@grinnell.edu with subject "CSC 151 Extra Credit". (Do not include the quotation marks.)
• Send opportunities to me before class with subject "CSC 151 EXTRA CREDIT OPPORTUNITY!"

Academic / Artistic

• Met Opera Simulcast, Saturday, March 5.

Peer

• Pub Quiz Wednesday at 10, hosted by Neuro/Psych SEPC. You can eat food, or pay to participate in the quiz ($3/team).

  Regular Peer

• Social Dance Workshop Tuesdays 7:00-8:00 in Bucksbaum Dance Studio

• Pun club Saturdays at 4pm in Younker
• Electronic Potpourri on KDIC Fridays at Five
• Space Odyssey KDIC Fridays at Six
• Fridays 7:30-8:30 Younker Lounge, Bollywood Dancing Team Fun Gathering

Misc

• Christine Tran show in Smith Gallery.
• Thursday evening Pub talk on Plans - Grinnell's own contribution to social media

Far in the Future

• Lords of the Flies, April.

No Extra Credit, But Still Good

Questions

Using image-compute

• A bit like image-variant
  • image-variant takes a function from colors to colors
  • image-compute takes a function from positions to colors
• Useful for making a few kinds of images

Demos!

> (define blend1
    (lambda (col row)
      (irgb (* 255 (/ col 200)) 0 0)))
> (image—show (image-compute blend1 200 200))

What do you think will this show?

• No blue component, probably no green as well
• Heavy black gradient until you reach right side where it becomes redder
• If we changed col w/ row, we would get a vertical gradient

> (define blend2
    (lambda (x y)
       (irgb (* 255 (/ x 200))
             0
             (- 255 (* 255 (/ x 200))))))
> (image-show (image-compute blend2 200 200))

What do you think will this show?

• It will fade from blue to purple to red because it will kind of invert it.
• That’s right!

> (define blend3
     (lambda (x y)
        (irgb (remainder (*10 x) 256) 0 0)))
> (image-show (image-compute blend3 200 200))

What do you think will this show?

• Maybe it’ll get this funky black to red type of thing that cycles?
• Yep!

> (define blend4
    (lambda (x y)
      (irgb (abs (- 255 (remainder (* 10 x) (* 255 2))))
            0
            0)))
> (image-show (image-compute blend4 200 200))

What do you think it will show? * It will kind of be like the last one where it cycles? * It will cycle by going up first then back down. * Unlike the last one where it goes from a sharp turn from red to black, it’ll slowly go back from red to black again

> (define blend4
    (lambda (x y)
       (irgb (abs (- 255 (remainder (* 10 x) (* 255 2))))
             (abs (- 255 (remainder (* 10 y) (* 255 2))))
             0)))

• We have a new component using the row. So we’ll get something that looks like a cheesy high school background

We can do stuff other than cool blends.

> (define thing1
        (lambda (x y)
                (if (and (> x 50) (< x 100) (> y 50) (< y 100))
                (irgb 255 0 0)
                (irgb 0 0 255))))

What will this show?

• Two different sections, red and blue.
• Red square in a blue background

> (define thing2
    (lambda (x y)
      (let ([num (remainder (truncate (/ x 20)) 3)])
        (cond 
          [(= num 0) 
           (irgb 255 0 0)]
          [(= num 1) 
           (irgb 0 255 0)]
          [else 
          i (irgb 0 0 255)]))))

What will this show?

• It’ll be cycling like we’ve seen.
• If it lands on a 0, it’ll be red.
• If it lands on a 1, it’ll be green.
• Otherwise, it’ll be blue.

> (define thing3
        (lambda (x y)
                (let ([num (remainder (truncate (/ x 20)) 3)]
                        [comp (* 255 (/ y 200))])
                (cond ((= num 0)

Lab

Writeup: Problem 3 (Class 22)