Held: Wednesday, 25 February 2015

Back to Outline 21 - Naming Local Values. 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
• Morning EBoard 22 (Source a.m. 22)
• Afternoon EBoard 22 (Source p.m. 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

• New partners (who will also serve as homework partners)!
  • Separate cards for those who do and do not want a HW partner
• Quiz Friday! Conditionals, higher-order procedures and let.
• Review sessions Thursday 9:00 a.m., 1:15 p.m., and 8:00 p.m.
• Office hours Today at 10:00 a.m.
  • http://rebelsky.youcanbook.me
• Our graders say
  • "Please limit your lines to eighty characters!"
  • "Remember that we are going to copy and paste your work into DrRacket. So don't add things after you copy and paste from DrRacket."
• Your peers say
  
  • "It's really helpful to save your work from the interactions pane."
  • "Copy-paste-comment"
• I plan to distribute an answer key to HW 5 tonight (or when the last homework comes in).

Upcoming Work

• Homework 6.
  • Due Tuesday at 10:30 p.m.
• Exam 2 to be assigned in a week.
• Lab writeup for today: Problem 3, http://bit.ly/151-2015S-lab22
• Reading for Friday
  • Building Data Structures with Heterogeneous Lists

Extra Credit Opportunities

Academic

• Pioneer Diversity Council Diversity Dialogue, 8:30 p.m. Thursday the 26th, Main Quad "Academic Athletes and Academic Students".
• CS Table Friday - Art, CS, and Artificial Intelligence.

Peer Support (Morning Section)

• Julia's radio show, "The Hot Box". Wednesday night/Thursday morning 1:00-2:00 a.m.
• Host a prospie.
• Indoor Track this Saturday
• Neverland Players Friday and Saturday at 7:30, Sunday at 1:30 and 7:30
• Nobody Gets Hurt, a show with an audience of one. Info on trying to get one of the tickets is on the posters.
• Orchestra in a week and a few days.

Peer Support (Afternoon Section)

• Indoor Track this Saturday

Other Good Things

• Neverland Players this weekend.
• Jazz band Thursday night.

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, use a function to determine a color for the pixel at (x,y).
• Syntax: (image-compute *function* *width* *height*)
  • No exclamation point because we are not changing anything that alread exists; we are simply computing a new image.

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.