Held: Tuesday, 23 September 2014

Back to Outline 14 - Transforming Colors. On to Outline 16 - Homogeneous Lists: Making and Manipulating Groups of Drawings .

Summary

Today we consider some basic control stuctures that will allow us to write more general image filters.

Related Pages

• Reading: Transforming Images
• Lab: Transforming Images
• EBoard (Source) (HTML)

Overview

• Transforming images by transforming each pixel.
• Sequencing transformations with compose.
• Anonymous transformations.

Administrivia

• Continue lab partners.
• No Sam tomorrow. Prof. Weinman will run class.
• Office hours: Thu/Fri 1:45-3:15; Also walking hours Thu/Fri 1:15-1:45.
• I've started a short reference on error messages. Please feel free to pass along some you get.
• Two important recent comments from students.
  • "I realized that it would be much easier to do the test and study for quizzes if I took notes along the way."
    • Sam's followup: There's evidence that you learn simply by taking notes (at least if you take notes by hand).
    • Sam's followup: Many of you reread labs and readings in preparation for the quizzes. I expect that read+notes+review notes takes less time than read+read.
  • "In high school, I did homework at night (or in the early morning). I learned that I'm much better off doing homework in my open slots during the day, rather than waiting until night time."
    • Sam's followup: You're also more awake during the day.
    • Sam's followup: There's more help available during the day.

Upcoming Work

• Lab writeup: Exercises 4a, 5b, and 5e http://bit.ly/151-2014F-w15 Due Friday.
• Exam 1 due Tuesday night.
  • Bring printed copies on Wednesday.
• Reading for Wednesday:
  • Making and Manipulating Homogeneous Lists

Extra Credit Opportunities

Academic

• Convocation Wednesday: Tara Zahra on Emigration from Eastern Europe
• CS Extras Thursday at 4:30: Mathematical Image Synthesis Toolkit (MIST)
• CS Table Friday at noon: ???
• Campus Town Hall September 30

Peer Support

• Noteworthy, Sat., Sept. 27, 3:30 p.m. Herrick
• Science poster session, Sat., Sept. 27, morningish, science elbow
• Football Games (Saturday, Sept. 27, at 1pm)
• Men's Tennis (???)
• Women's Tennis (???)
• Swimming (???)
• Anna Christie, Oct. 9-12 (SB plays Marthy)
• Evan's radio show 5pm Friday nights on KDIC
• Donna's radio show Sunday midnight on KDIC

Miscellaneous

• Participate in #GrinWell. http://www.grinnell.edu/forms/sign-grinwell-presidents-wellness-challenge
• Friends of Drake Library needs help setting up for their annual booksale on Thursday, October 2 (conveniently, the same night as Grinnell High School's homecoming parade). You can help a good cause and probably get a few free books, too.
  • Update: They can also use help on Wednesday, October 1.

Transforming images by transforming each pixel

• We saw in the color transformation lab that we can apply a transformation to each pixel, getting it and then setting it to a new value.
• This generalizes that strategy.
• (image-variant image color-transform) - build a new image by applying color-transform to every pixel.
• image-transform! image color-transform - change the pixels "in place"
• Interesting new concept: We can write procedures that take other procedures as parameters.

Sequencing transformations with compose

• When you need to do more than one transformation, you can sequence them with compose (also o).
• (image-variant image (o rgb-redder rgb-bluer))
• Note: This is a new approach. Traditionally, procedures appear immediately after parentheses, and they are doing the work. Now they are inputs to other procedures, and so do not have parentheses.

Anonymous transformations

• You don't even need to name those transformations.
• (image-variant image (lambda (rgb) ...))