# Laboratory: Algorithmic Art

This laboratory is also available in PDF.

Summary: We explore two techniques for algorithmically generating interesting images: Random drawing and Color grids.

Contents:

## Preparation

For this laboratory, you will need to have a copy of grid.scm in your GIMP scripts folder.

a. Open a new terminal window.

b. Type

ln -f -s /home/rebelsky/Web/Courses/CS151/2007S/Examples/grid.scm .gimp-2.2/scripts/grid.scm

c. Start GIMP and verify that the Xtns/Script-Fu menu contains a Glimmer submenu.

## Exercises

### Exercise 1: Color Grids

a. Set the current brush to a medium circle.

(set-brush "Circle (09)")

a. From the Xtns menu, select Script-Fu, then Glimmer, and finally Color Grid. A dialog box should appear. Enter 100 for the width and height, and 10 for the horizontal and vertical spacing. Observe the image that appears.

b. What do you expect to happen if you use 8 for the horizontal and vertical spacing? Confirm or reject your prediction experimentally.

c. Set the current brush to a larger fuzzy circle.

(set-brush "Circle Fuzzy (15)")

d. What do you expect to happen if you again use 8 for the horizontal and vertical spacing? Confirm or reject your prediction experimentally.

e. What do you expect to happen if you use func3 for the red component (continuing to use func2 for green and func3 for blue)? Confirm or reject your prediction experimentally.

f. Try one or two other brushes and one or two other arrangements of functions.

### Exercise 2: Specifying Components

a. With DrScheme, create a new file on your desktop, components.scm.

b. Add the following function to that file.

(define func4
(lambda (x y)
(modulo (+ (* 3 x) (* 5 y)) 256)))

c. Make a link to that file in your Script-Fu scripts folder by opening a new terminal window and typing the following command:

(You only need to do this once, but it makes sure that the GIMP knows about the file.)

d. Refresh scripts by selecting Xtns->Script-Fu->Refresh Scripts. (You will need to refresh scripts whenever you change components.scm.)

e. Verify that you can now use func4 in building a Color Grid.

f. Add the following procedure to components.scm.

(define func5
(lambda (x y)
(modulo (* x (abs (sin y))) 256)))

g. Verify that you can use this procedure. (If you can't remember that you need to save the file and to refresh scripts.)

### Exercise 3: Anonymous Components

As you may have noted from the previous exercise, it can be a bit of a pain to remember to save and refresh every time you define a new component function. As the reading suggests, we can instead use anonymous functions.

a. Open the Color Grid dialog box, use the following for the red, green, and blue components, and then display the grid.

• (lambda (x y) (modulo (* x 5) 256))
• (lambda (x y) (modulo (* y 5) 256))
• (lambda (x y) 0)

b. Try some functions of your own design. Remember that each function has the form (lambda (x y) expression) and that the expression should return a value in the range [0..255].

### Exercise 4: Making Grids from the Console

Some people (myself included) prefer to generate their grids from the console. As you may recall from the reading, the color-grid procedure has seven parameters:

• the width of the image
• the height of the image
• the horizontal spacing between points
• the vertical spacing between points
• the red component function
• the green component function
• the blue component function

For example, here's the command that we might use for the first grid we drew (100x100, 10x10 grid)

(color-grid 100 100 10 10 func1 func2 func3)

a. Try that example.

b. Try varying the parameters (e.g., using a different width, height, spacing, or function).

c. Try using lambda expressions for the functions. For example

(color-grid 100 100 8 9 (lambda (x y) (modulo (* x y) 256)) (lambda (x y) (modulo (* x 5) 256)) (lambda (x y) (trunc (* 255 (abs (sin (* x y)))))))

## History

Disclaimer: I usually create these pages on the fly, which means that I rarely proofread them and they may contain bad grammar and incorrect details. It also means that I tend to update them regularly (see the history for more details). Feel free to contact me with any suggestions for changes.

This document was generated by Siteweaver on Thu Sep 13 20:54:14 2007.
The source to the document was last modified on Mon Apr 9 10:28:01 2007.
This document may be found at http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2007S/Labs/algorithmic-art.html.

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Samuel A. Rebelsky, rebelsky@grinnell.edu