Held: Monday, 16 February 2015

Back to Outline 15 - Boolean Values and Predicate Procedures. On to Outline 17 - 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
• Morning EBoard 16 (Source a.m. 16)
• Afternoon EBoard 16 (Source p.m. 16)

Overview

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

Administrivia

• New partners!
• Mentor session Monday at 7:00 p.m.
• Just in case it's not clear: If I find that you have posted your exam work online, including via social media, I will report you for ethical violations and, unless prevented by College policy, will fail you in the class.
• Friday the 13th falls on Friday next month. Be careful.
• Exam 1 to be returned tomorrow.
• Congrats to all of our athletes who competed this weekend.
• We'll do a quick debrief on some learning outcomes from Friday's class.

Upcoming Work

• Homework.
  • Due Tuesday night at 10:30 p.m.
• Lab writeup for today:
• Reading for Tuesday:
  • Making and Manipulating Homogeneous Lists

Extra Credit Opportunities

Academic

• TEDx Grinnell, February 21
• Pioneer Diversity Council talk

Peer Support (Morning Section)

• Julia's radio show, "The Hot Box". Wednesday night/Thursday morning 1:00-2:00 a.m.

Peer Support (Afternoon Section)

• Men's Basketball vs. Knox, Wednesday at 7:30 p.m., New Darby

Other Good Things

• Women's Basketball vs. Knox on Wednesday.

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) ...))