Digital Editing using GIMP by ruQHFFI


									C/IL 102 Lab                                                         Summer I 2007
Digital Editing using GIMP

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 where you can
download an appropriate version for your computer – Windows (NT, 2000, and XP),
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:

                                                      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

                                                      The GIMP Website has a great
                                                      deal of help in learning the
C/IL 102 Lab                                                         Summer I 2007
Digital Editing using GIMP
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 on Dr.
Sidbury’s C/IL Web Site located at 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, located on the same web
site. 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. Open a Web browser to Dr. Sidbury’s Web site
       and highlight C/IL 102 and click Lab Info.
            b. Scroll down to Lab 12 and right click on the two llinks Giraffe Picture and
                Picture of Buster. Choose the option to download them to your desktop.
    2.      Open the GIMP by clicking start and then Desktop Publishing 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 or if the Brushes, Patterns, Gradients is not open
            then open them as follows: click file >Dialogs>Create New Dock and then
            open which ever one is missing. Open both if both are missing. In the
            pictures associated with this document they are both open and combined into
            one window.
    3.      Click on the file menu, choose OPEN, and select Giraffe.png from the
    4.      Your desktop should look something like the following:

                                       The title bar of the picture should say
                                       something like Giraffe.png-3.0 (RGB, 1 layer)
                                       3024x1998. The file name containing the
                                       picture is Giraffe.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.
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.
C/IL 102 Lab                                                         Summer I 2007
Digital Editing using GIMP
   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.
          d. Show the results to your instructor.

This should change the size to 500 x 330. Click file > save as > and name it
Giraffe1.png and save. 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.     Now undo all the changes that you’ve made.
          a. Selet>Undo Scale Image. You should now be back where you were
   7.     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.
C/IL 102 Lab                                                            Summer I 2007
Digital Editing using GIMP
          d. You can save the image in another format such as GIF, TIFF, PSD, PNG,
              JPG and several others. The advantages of various formats are
              discussed in Tao of Computing chapter 2.
   8.     Crop the image – i.e. choose part 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 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. Click crop on the
              crop window. If you click edit you can undo the crop and start over.
          b. Show the cropped result to your instructor.
   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                                                           Summer I 2007
Digital Editing using GIMP

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 eye-droppers,
                                        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.
          g. How to make a greyscale version of a picture
C/IL 102 Lab                                                        Summer I 2007
Digital Editing using GIMP
                   i. Easy way. Right click the picture of Buster, choose image, choose
                      mode, select grayscale.
                  ii. Hard Way. Right click the picture, choose Image, choose mode,
                      choose decompose. Choose RGB and make sure that
                      decompose to layers is checked. Click OK.
                 iii. This should open a new window named red-4.0 (grayscale, 3
                                             layers) and it’s gray. If you look at the
                                             layers, channels, paths… window it should
                                             have red-4 (or whatever) listed at the
                                             top.and 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.

                                        iv. Redo this problem except choose HSV
                                            as the decomposition 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
                v. 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 Script-fu > décor > old photo. This
                    brings up a window: Script-Fu: 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.
                vi. Show the results to your instructor.

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