Outline 07: Transforming Images

Held: Tuesday, 8 September 2015

Summary

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

Related Pages

Overview

Administrivia

Continue partners!
Mentor sessions Wednesday and Thursday at 8pm in the Commons.
Sam review session Thursday at 10am in our classroom.
We'll spend the start of tomorrow's class going over some of the key ideas from the past week. Bring lots of questions!
I'm working on a virtual machine that you can use to do your 151 work outside of Noyce 3rd. It just requires a few hours of my time, which have been hard to find.

Two readings for Wednesday: Procedures How Scheme Evaluates Expressions (take 2)
Assignment 2 due tonight @ 10:30 p.m.
Assignment 3 to be released tomorrow.
Lab writeup (due before class Friday)
- Email to grader-151-01@cs.grinnell.edu (not to me; don't forget the cs).
- Subject: CSC 151 Lab Writeup Class 7 (Your Names)
- Problems:

Pals of PALS, pals@grinnell.edu, normally Saturday at 1:30 and Mondays at 4:45. Requires sign up in advance.
Pun Club, Saturdays, 4pm, Way over Younker

All of these notes come from the old model of this course.

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.

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.