Class 39: Manipulating Images with Script-Fu

Held: Wednesday, April 11, 2007

Summary: Today we consider some procedures for manipulating existing images.

Related Pages:

• EBoard.
• Lab: Manipulating Images with Script-Fu.
• Reading: Manipulating Images with Script-Fu.

Notes:

• If you got at least a B on the exam, you should think about going on to the wonders of CSC152 in the fall.
• If you needed the "There's more to CS" fix, consider getting a Tutor or setting up a regular appointment with me.
• Are there questions on Homework 12?

Overview:

• Primary image-manipulation procedures.
• color transformations.
• Lab.

Manipulating Images Programmatically

• Each image that the Gimp creates is effectively just a two-dimensional grid of color values.
• Hence, we can do interesting things using those color values.
  • We can generate those color values using some formula.
  • We can modify those color values using some formula.
  • We can move those color values around.
• I call the use of algorithms to accomplish those and similar purposes algorithmic art.
• I've built a number of procedures to help with those purposes.
• The procedure (get-color-at image x y) gets a color from an image.
• The procedure (set-color-at! image x y color) sets a color in an image.
• The procedure (modify-image! transform image) applies transform to every point in the image.

Color Transformers

• There are a vareity of techniques for transforming colors.
• We build a color with (rgb red green blue)
• We extract the components with (red color), (green color), and (blue color).
• When we write our transformers, we can use a variety of techniques
  • anonymous procedures
  • curried procedures
  • sectioned procedures
  • procedure composition
• For now, you'll start to learn the basic ways to use these procedures.
• Soon, you'll learn some theory and practice.

Lab

• Questions?
• Do the lab.