This lab is also available in PDF.
Summary: In this laboratory, you will explore some issues with
the creation and modification of simple raster graphics, primarily in
terms of the creation and analysis of colors.
Reference:
Contents:
Start DrFu (which starts The GIMP and the DrScheme interface for
programming). If you've forgotten how to do so, review the first DrFu lab.
For this laboratory, you will need to work with two images.
a. Using the techniques described in the corresponding reading, create and show a 9x5 image called landscape.
Recall that (image.new width height) creates
an image and (define name expression) assigns
a name to a computed value.
b. As you may recall, the initial color associated with an image is the
current background color. Change the background color to yellow in
preparation for the next step.
Recall that (envt.set-bgcolor! color) sets
the background color and that (cname->rgb name)
lets you get a color by name.
c. Using the same technique that you used for step a, create and
show a 5x7 image called portrait.
a. Make the top-left pixel of each of the two images red. Recall that
you set pixels using (image.set-pixel! image column
row color) and that you can get a color from its
name with (cname->rgb "name").
b. Make the bottom-right pixel of each of the two images black.
c. You may have found that it is difficult to see the changes that
you've made. To better observe these changes, let us enlarge
the picture.
- Click on the picture to bring it to the front.
- From the menu at the top of the window,
select the submenu and then select
Pick one of your two images and write instructions to make a green
plus sign in the exact center of the image. The plus sign should be three
pixels wide and three pixels high.
As you may recall from the reading, the (cname.list name)
procedure lets you find out all the color names that DrFu knows about that
include name. For example, (cname.list "red") will
tell you about various red-like colors.
Set the upper-right corner of each image to one of those variants of red.
Of course, you should not be limited by our suggestions for possible colors.
Write down the names of five of your favorite colors and then see if any
of them are defined by using cname.list.
a. Using those results or other explorations of the DrFu color space,
pick three color names that you like, find the corresponding RGB values,
and name them fave1, fave2, and fave3.
For example, if spicy pink were my favorite color, I might write
(define fave1 (cname->rgb "spicy pink"))
You may find it easiest to look at colors using envt.set-fgcolor!.
For example, if I wanted to see what spicy pink looked like, I might use
(envt.set-fgcolor! "spicy pink")
b. Set some pixels to your favorite colors.
c. Create a new file, /home/username/Desktop/fave-colors.sct, that contains these
three definitions. You may want to review the
DrFu lab for how to save definitions.
Recall that you can find out the value DrFu associates with a name by
typing it in the interactions window and then hitting enter.
a. Find out what values DrFu associates with your three favorite colors.
b. Are those values clearer or less clear than the names you've used?
c. (Optional) Hypothesize what those values represent.
As you may recall from the reading, one way we deal with the lack of
clarity of color values is to use the rgb->cname
procedure to find the name of a similar color.
Verify that rgb->cname successfully finds the names of
your three favorite colors.
The (image.load "file-name") procedure allows us to
load an image from a file. As is the case with create-image,
load-image does not immediately show the image it has loaded.
And, as is the case with image.new, you'll need to name
the image you've just loaded.
a. Load the image /home/rebelsky/glimmer/samples/rebelsky-stalkernet.jpg, name
it sample, and show it in a new window.
b. Save your StalkerNet picture to /home/username/Desktop/me.jpg, load that picture, name it self-portrait, and show it in
a new window.
How do you save your StalkerNet picture? You first find yourself in
StalkerNet. Next, you right click on the picture, select from the menu that appears, navigate to the desktop, and
choose the name me.jpq..
Although Grinnell College owns the copyright in your StalkerNet picture and tells us so repeatedly in strong language, our use of that picture for this lab and elsewhere in the class clearly falls under the rubric of fair use.
c. Set the bottom-left pixel in each of the two new images to white.
a. Set the color of the center pixel in portrait to the
color of the center pixel in self-portrait. (If there is
not a center pixel in self-portrait because it has even
width or height, use one near the center.)
b. Find out the name of the color of some pixel in
self-portrait using image.get-pixel and
rgb->cname.
Explorations are intended for students interested in further
exploring the design aspects of these techniques. They also
provide students who finish early with extra activities that may
challenge them in different ways.
Create a new 9x5 image called canvas. Fill the pixels of
the canvas with variations of blue to produce something you find
compelling.
If those instructions are too vague, you might consider how to use those
shades of blue to make an image that induces some mood, such as relaxation
or playfulness.
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