This laboratory is also available in PDF.
Summary: We explore two techniques for algorithmically
generating interesting images: Random drawing and Color grids.
Contents:
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 menu contains
a submenu.
a. Set the current brush to a medium circle.
(set-brush "Circle (09)")
a. From the menu, select ,
then , 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.
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:
ln -s /home/username/Desktop/components.scm .gimp-2.2/scripts/components.scm
(You only need to do this once, but it makes sure that the GIMP knows about
the file.)
d. Refresh scripts by selecting ->. (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.)
h. Add a few of your own interesting
component functions.
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].
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)))))))
;
