Outline 07: Transforming Images

Held: Wednesday, 3 February 2016

Summary

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

Related Pages

Overview

Administrivia

Office hours: MTWF 10-11, Tu 1-2.
- Sign up at http://rebelsky.youcanbook.me.
- Also feel free to stop by when my door is open.
- Or to email me for an appointment.
Tutor hours
- Sunday, 3-5 p.m.
- Sunday-Thursday, 7-10 p.m.
Weekly review sessions:
- Wednesday at 8pm in the CS Commons with Zacharcy
- Thursday at 10am in this room with SamR
- Thursday at 8pm in the CS Commons with Kumar

Quiz Friday
- Topics
  - Scheme's order of evaluation and sequencing.
  - Definitions (in Scheme).
  - Arithmetic operations, including things like max, min, floor, ceiling, round, quotient, and remainder.
  - RGB colors, and the operations on integer-encoded RGB colors.
  - Basic RGB transforms (although we will remind you of what they do): irgb-redder, irgb-greener, irgb-bluer, irgb-darker, irgb-lighter, irgb-complement, irgb-rotate, irgb->string
  - Function composition.
- Form
  - Closed book
  - Possibly: "evaluate this expression (or series of expressions)"
  - Possibly: "using composition, write a procedure to compute ..."
  - Possibly: "given this definition, what does this procedure do?"
Readings for Friday:
- Writing Your Own Procedures
- How Scheme Evaluates Expressions (v2)
Assignment 3 due next Tuesday at 10:30 p.m. (Your assignment partner is your partner from today.)
Lab Writeup: Exercise _
- Send email titled CSC 151 Lab Writeup _ (Your Names)
- Do not include the underscores.
- Send to CSC151-02-grader@grinnell.edu
- Due before class on Monday.

If you know of other events, please suggest them! (I might not always agree, but it never hurts to ask.)

4 pm Thursday in this room: LaTeX
4 pm Thursday in JRC 209 - Funding for unfunded internships
Next week's Rosenfield Symposium on Campaign Finance Reform.
noon Tuesday in the White PDR: Bowie, Mickey, and more: Copyright in the 21st century
7:30 pm next Tuesday in ARH 131 - Funding for unfunded internships

Social Dance Workshop Tuesdays 7:00-8:00 in Bucksbaum Dance Studio (starting next week)
Pun club Saturdays (max 2)
Socrates Cafe' Saturdays (max 2)

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.