C/IL 102 Lab
Digital Editing using GIMP
Spring 2011
Digital Editing using GIMP
GIMP (GNU Image Manipulation Program) is a program similar to Photoshop or PaintShop
PRO (except that it’s free). The two primary uses that we will study in this lab will be to create
logos and to modify existing digital photographs. If you would like to have GIMP on your own
computer you may go to http://www.gimp.org where you can download an appropriate
version for your computer – Windows (NT, 2000 XP and Vista), Mac OS X, or Unix (including
Linux). The images in this lab are from a macintosh version of GIMP but are very similar to
the Windows version that you will be using in the lab. The GIMP has a very different
interface from typical applications such as Word or Excel. It uses several windows rather
than only one. This will probably take some getting used to, but many people prefer
applications that work this way especially on a screen with higher resolution (such as
1024x768 or 1280x1024). In my opinion, this method is much easier to use on a system with
multiple monitors. When you first start the GIMP you should have a desktop that looks
something like the following:
Each of the Windows has a specific function and they can be resized or moved around
separately so that for example you may create a setup that looks like the following:
C/IL 102 Lab
Digital Editing using GIMP
Spring 2011
If you double-click on one of the toolbox
icons, its tool options window will
appear. As you change from one tool
to another the tool option changes
appropriately.
The GIMP Website has a great deal of
help in learning the intricacies of the
program. There are several books,
some available to be read online, and
several tutorials. If you wish to become
proficient with this program I
recommend that you examine these
sources.
You will first manipulate two photographs. There is a photograph of a giraffe, named
Geoffrey. This file is 29 megabytes in size and if you were to place it on a Web site it would
probably take more than 5 minutes to load. There is also a picture of a kitten, Buster.
Buster.jpg is only 384 kilobytes in size and should take 10 or 20 seconds to load depending
on network traffic.
1.
Download both photos to the desktop.
a. On your instructor’s page click on the two links Geoffrey Giraffe and Buster.
Save them to your desktop.
2.
Open GIMP2 by clicking the start menu and then All Programs and then choosing
GIMP. If the program comes up with a full screen menu whose title bar says “The
GIMP” then grab the title bar and move it slightly to the left to bring the right edge
of the window on the screen. Then resize the window so that there are about 6
icons across on the toolbar. If the Layers, Channels, Paths window is not open,
click the “Windows” menu and then “Recently Closed Docks” Open both if both are
missing.
3.
Click on the file menu, choose OPEN, and select Giraffe.png from the
desktop.
4.
Your desktop should look something like the following:
The title bar of the picture should say
something like Geoffrey.png-3.0 (RGB, 1
layer) 3024x1998. The file name containing
the picture is Geoffrey.png. The picture is a
single layer. If we could separate the picture
into several layers, such as one for the
background, and another for the giraffe. By
doing this you can modify each layer
individually and then combine them back
together or replace one with something else,
so for example you could place the giraffe in
the desert. The size of the picture is 3024
pixels wide by 1998 pixels high.
C/IL 102 Lab
Spring 2011
Digital Editing using GIMP
NOTE: By pointing to a picture and pressing control-D you will create a duplicate of
the picture which you can manipulate thus preserving the original. You should
probably do this to all the exercises using photographs.
5.
Change the dimensions of this picture as follows:
a. In the menu above the picture click on Image and then select Scale Image.
This should open a new window with Image Size listed as 3024 wide and 1998
high in pixels. Beside the dimensions is a chain with two links connected. If you
click on the chain the links will be disconnected. If you click again they will
reconnect. If the links are connected, changing one dimension automatically
changes the other proportionately. This preserves the aspect ratio of the
picture. (The aspect ratio is the ratio of the width to the height.) If the aspect
ratio is NOT preserved then the picture will be distorted, so that for example if
you increased the height proportionately more than the width then the giraffe
would become taller (and skinnier). Normally you will want to preserve the
aspect ratio so the link should be connected.
b. Let’s cut ths size to 500 wide. Highlight the 3024 and type 500. The height
should change to 330 automatically after a few seconds. The units are pixels
but can be changed to inches, millimeters, percent and other choices. Now click
the arrow beside interpolation and change the choice from linear to Cubic.
This choice determines the quality of the finished picture. Cubic gives higher
quality but takes longer to do.
c. Finally click scale. This should change the scale of the picture (and
simultaneously reduce its size). If you now click Edit the first choice in the Edit
menu is Undo Scale Image. Thus if you make a mistake you can undo it and
start over. This feature is available for almost all GIMP manipulations and when
combined with working on the duplicate of a picture ensures that the original will
be preserved. If you clicked the UNDO then go back to step b and redo the
Scale Image.
This should change the size to 500 x 330. Click file > save as > and name it
geoffrey_resized.png and save to the desktop. Right click the picture’s icon and you will
see it’s size is now only about 336K a reduction in size of more than 98 percent.
6.
7.
8.
Now undo all the changes that you’ve made.
a. Select>Undo Scale Image. You should now be back where you were before
Now change the type of file that you have.
a. click File and then select save as
b. now type the name Giraffe.jpg (to change the type of file from png to jpeg) and
click save.
c. This should bring up another window, Save as JPEG. The quality slider should
be somewhere near 85. Click OK and this will save the picture on the desktop.
It’s now 1.5 megabytes (and still 3024x1998 pixels), a reduction of
approximately 95 percent.
Crop the image – i.e. cut the giraffe out of the picture.
a. Bring the tool bar to the front and select the crop tool (it looks sort of like a knife.
When you move your cursor over the picture it will change into a plus. Now
C/IL 102 Lab
Spring 2011
Digital Editing using GIMP
move the cursor above and to the left of the giraffe and press and hold the left
mouse button. Drag the button to the right and down until you have covered
Then release the mouse button. Either click “crop” in the window or press
“Enter” on the keyboard. If you click edit you can undo the crop and start over.
b. Change the file type back to PNG and save the cropped picture as
geoffrey_cropped.png to your desktop.
9.
Play time. Many times you will take a photograph that is technically unsatisfactory
– the color balance is wrong, the contrast is wrong, the brightness is wrong, the
saturation is wrong … you get the idea. We will now use several techniques to
“improve” our pictures.
a. Open the picture of Buster that you saved on your desktop, and make a
duplicate of it. You will “play” with the duplicate.
b. Click layer>colors>auto and you should see a result similar to the above
picture. Choose each of the above and look at the result and then UNDO it.
Equalize will probably give very weird results which may look spectacular with
some pictures but strange with most pictures. The others make subtle
adjustments.
c. A more sophisticated way of manipulation can be done by clicking Tools >
Color Tools > Levels. This will bring up the levels window:
C/IL 102 Lab
Digital Editing using GIMP
Spring 2011
This window has several ways of
modifying the picture. First click the
AUTO button and the picture will be
automatically enhanced. Click the
RESET button below to undo this
change. If the Preview checkbox is
checked then changes that you make
will be shown on your copy.
Beside the auto button are three eyedroppers, the first for black the second
for grey and the third for white. Click
the black eyedropper and then point to
a part of the picture that should be black
and click. (I chose a spot in Buster’s
eye.) By choosing other points
interesting results can be obtained: try
to use black with a spot on the wooden
floor to see what I mean. Redo this with
the white as well. A very good color
adjustment can be done by doing a
black balance followed by a white
balance. Note that after you finish
doing the last dropper change you
should click the dropper to turn it off.
d. There are two sliders, one just below the graph with three triangles just below
the slider and below it a black dropper a white dropper and three number
windows. You can move the sliders by changing the numbers or picking a
black and white reference point or by just grabbing them and moving them. If
you click the Reset channel above this sets the values back to their original
values. You can also change the channel value to Red or Green or Blue and
make changes to them for “artistic” results. Set the channel to Red and move
the middle triangle to the left about half way (2.94 is the value I found) and look
at the result. Now move it to the right about half way to the end (.34 is
approximately where I went). Then reset the channel. Make changes to
several channels together and observe the results.
e. If the exposure had a low shutter speed there is a possibility that the picture is
blurred. In general if the picture is too blurred there is nothing you can do.
However if the blur is slight you might be able to sharpen the picture slightly.
This technique should be uses sparingly. Click filters > Enhance > Unsharp
Mask. (I know, unsharp sounds backwards but this is the best tool for
sharpening the picture). Set the amount to 1, the radius to 1 and the threshold
to 0 and click OK. Reset it and redo the problem with the amount set to 5. The
picture is now sharper but very unrealistic.
f. If the picture is too sharp you can blur iit by simply choosing filters > blur > blur.
And repeat as often as necessary.
C/IL 102 Lab
Spring 2011
Digital Editing using GIMP
g. How to make a grayscale version of a picture
i. (a) Easy way. Right click the picture of Buster, choose image, choose
mode, select grayscale.
(b) Hard Way – if you’re brave. In the Colors menu, choose
Components and Decompose. Set your color model as RGB and
be sure Decompose to Layers is checked. Click ok. This should
pop up a grayscale image of Buster. If you look at the layers,
channels, paths… window there should be three pictures below it
labeled blue, green, red with eyes on the left: at the moment each of
the layers is visible. If you click on one of the eyes that particular
layer will be hidden from view. Click on each of them and you should
see a gray and white checkerboard. Now click on the (invisible) eye
beside the red picture and you see just the red layer. Close that eye
and look at each of the other layers. Often the Green layer is a very
good grayscale image.
ii. Redo this problem except choose HSV as the
color model and look at the value layer. It also produces a good
grayscale. You might also look at the other two layers to see what
they produce. Other decompositions produce interesting grayscale
pictures.
iii. Sepia tone gives an old time look to a picture. It
is a long complicated process that can be automated via a script.
Choose a picture of Buster and select Filters > décor > old photo.
Make sure that Sepia and Work on Copy are both checked. Defocus
and also be selected if you wish. Set border size to 30 and click OK.
iv. Save the photo as buster_sepia.png to your desktop.
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