This lab is also available in PDF.
Summary: In this lab, you will experiment with
GIMP, the GNU Image Manipulation program. You will also think about
how you might give instructions to someone else to draw pictures using
GIMP.
Contents:
Because of the timing of this lab, no preparatory reading was available.
Hence, this lab begins with a few short notes. A longer optional reading is also available.
The GNU Image Manipulation Program (GIMP
, for short) is an
open-source, freely-distributed graphics editing program that can serve
as a reasonable alternative to Adobe Photoshop. Like Photoshop,
GIMP provides tools for both making new images and for manipulating
existing images.
GIMP distinguishes itself from Photoshop in three key ways: First,
it is an open source application, which means that you can get it for free
and (if you have enough talent) can even modify the source code. Second,
it is available on all three major operating system platforms (Mac, Windows,
and Unix/Linux). Third, and perhaps most importantly for this course,
GIMP is scriptable. In particular, you can interact with
GIMP using a Scheme-like language. You can use this language to give
simple commands or to write complex scripts.
We will explore these applications over the coming weeks.
a. Open a terminal window by clicking on the picture of the computer
screen in your task bar.
b. Start GIMP by typing gimp. It will probably ask you
whether it can install some files. Allow it to do so.
c. Play for awhile with the various tools. Feel free to share
ideas and questions with neighbors.
The GIMP relies on its selection tools to support a variety of kinds of
drawing. You may have noted that there are three selection tools: A
rectangular tool, an oval tool, and a freehand (lassoo) tool. The
strategy one normaly uses is to select some area and then fill or
stroke that area.
a. Create a new image.
b. Set the foreground and background colors to something recognizable (say,
red and green).
c. Choose an interesting brush (say, one of the Calligraphic brushes or
the Pencil Sketch brush).
d. Using the selection tool of your choice, select a moderately large
area of the screen.
e. From the menu, select . Observe what happens.
f. From the menu, select and click Stroke with a paint tool from
the dialog that appears. Choose the Paintbrush as the paint tool.
Click the Stroke button. Observe what happens.
g. Select different areas and stroke and fill with different colors,
paint tools, and stroke lines.
By default, when you select a second area, GIMP forgets the previously
selected area. However, there are ways to combine selections. In
particular, when you hold down the shift key, you get one behavior and
when you hold down the control key, you get another behavior.
a. Select a large rectangular area.
b. While holding down the shift key, select an overlapping rectangular
area. What happens? What does that suggest about selection with
the shift key?
c. While holding down the control key, select an overlapping rectangular
area. What happens? What does that suggest about selection with
the control key?
d. While holding down both the shift key and the control key, select
yet another overlapping rectangular area. What happens? What does that
suggest about selection with both keys?
e. Stroke or fill the area you've just created.
If you are unsure of any of your answers, you may wish to check
the notes on this problem.
Draw a smiley face using whatever tools you deem most appropriate.
a. Sketch, in English, instructions for replicating the drawing you
just made. (You can assume a reasonably competent reader. While
I may attempt to replicate your instructions, I won't do my normal
imitation of a sentient but malicious computer
or of a clueless
computer scientist
.)
b. Share your instructions with neighboring groups.
c. Using one of the sets of instructions you received from a
neighboring group, make a new drawing.
Start with the word Computer Science and make an interesting logo. You
might add colors, shadow, more. You might find the
and menus useful.
Sketch, in English, instructions you might give someone else to create
a logo like that.
Generalize your instructions from the previous step so that they could
be used with any word.
The shift key serves as the add modifier. The newly selected
area is added to the previous selection.
The control key serves as the remove modifier. The newly selected
area is removed from the previous selection.
The combination of the shift key and the control key is the
intersection modifier. Only stuff that is both in the the
previously selected area and the newly selected area is selected.
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