Held: Tuesday, 24 September 2013

Back to Outline 14 - Transforming Colors. On to Outline 16 - 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
• EBoard (HTML) (PDF)

Overview

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

Administrivia

• Continue lab partners!
• I'm going to have an optional class this Thursday at 1:15 (and, I hope, most Thursdays) as a chance to talk to folks about more things that might be useful or interesting.
• Work for Wednesday:
  • Finish the exam.
  • Reading for Wednesday: Making and Manipulating Homogeneous Lists
  • Lab writeup 5: Problems 4 and 7 from Transforming Images Due before class on Friday. (Ideally before class on Wednesday.)
• EC Opportunities:
  • CS Extras Thursday @ 4:30: Jennelle Nystrom on working at Microsoft
  • CS Table Friday (The Story of Mel)
  • Football, 1pm, Saturday against Beloit
  • Orchestra, 2pm, Saturday, Sebring-Lewis or somewhere similar
  • Folksyish music with Seth at Relish, Wednesday at 10pm
  • Knitting club, Saturday at 10am. Do good and have fun!
  • More ...?

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))

Anonymous transformations

• You don't even need to name those transformations.
• (image-variant image (lambda (rgb) ...))