Held: Tuesday, 25 February 2014

Back to Outline 21 - Anonymous Procedures. On to Outline 23 - Revisiting Lists.

Summary

We consider a simple approach to working with images - looping over the positions in an image and computing a new color based on positional information. We then explore some applications of this approach.

Related Pages

• Reading: Building Images by Iterating Over Positions
• Lab: Building Images by Iterating Over Positions
• EBoard 22 (Source 22) (HTML 22) (PDF 22)

Overview

• 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.

Administrivia

• Reading for Wednesday: Building Data Structures with Heterogeneous Lists
• Our computer system is (still) acting up. I have not received any clear indications as to when it will be healthy again.
• A few of you are frustrated that your indentation changes when you cut and paste into Google docs. If you use Chromium for accessing Google docs, cut and paste should work.
• Writeup: Exercise 4
  • Subject: CSC 151.02 Writeup 14: Iterating Positions (OPTIONAL NAMES)
• Extra credit:
  • Tuesday Town Hall, noon in JRC 101, 7:30 p.m. in Harris.
  • Tuesday wellness event.
  • Wednesday Royce Wolf concert.
  • Thursday CS Extras at 4:30 p.m. in 3821: New CS Curriculum.

Models of images

• We've seen a variety of models of images.
  • Images that we describe by composing basic shapes.
  • Images that we create by transforming existing images.
  • Images that we create by using the Gimp tools.
  • Images that we create by a combination of techniques.
• But there are certainly other models of image making. We'll learn at least two more this semester.
• Why are we learning so many models of image making? Because the basic operations you have affect the way you think about problem solving.

The image-compute model

• In the image-variant model, we built images with a starting image and a function from colors to colors.
• We will consider a variant of this model - images as functions from positions to colors.
• That is, given an (x,y) pair, determine a color for the pixel at (x,y).
• Syntax: (image-compute *function* *width* *height*)

Examples

• Color blends are the most natural thing to make.
• We can also make shapes by using conditionals.
• Given that colors are just numbers, we can also just do numeric computations and see what they give us.