Working with the Gimp

The Red Hat Linux 6 CD in the back of this book contains a terrific graphics tool called the Gimp. The Gimp— Gnu Image Manipulation Program—is a full-featured application along the lines of Adobe Photoshop. You can use to it create images, retouch photos, and much more.

Written by Peter Mattis and Spencer Kimball, the Gimp is as powerful as any comparable program available on any platform. Like Photoshop, it is a visual artist's delight. You can find some of the images that artists have created using it—as well as downloads and useful information—at the Gimp's Web site, http://www.gimp.org

When you set out to explore the Gimp on your own, you'll realize that it has many more features than could ever be covered in Red Hat Linux 6: Visual QuickPro Guide. (Indeed, the Gimp deserves a book of its own!) These features include:

• A complete set of painting tools, including Brush, Pencil, Airbrush, and Clone tools

• Tile-based memory management so image size is limited only by available disk space

• Anti-aliasing support for the highest quality rendering

• Implementation of full alpha channel support

• Layers and channels

• The ability to write scripts that can be invoked in the Gimp, and the ability to call Gimp objects and methods from external scripts (called Script-Fu)

• Multiple levels of Undo and Redo (limited only by available disk space)

• The ability to have a virtually unlimited number of images open at one time

• An extremely powerful gradient editor and Blend tool

• The ability to load and save animations in a convenient frame-as-layer format

• Transformation tools, including Rotate, Scale, Shear, and Flip tools

• Many supported file formats, including .gif, .jpg, .png, .xpm, .tiff, .tga, .mpeg, .ps, .pdf, .pcx, and .bmp

• The ability to load, display, convert, and save using many file formats

• Selection tools, including Rectangle, Ellipse, Free, Fuzzy, Bezier, and Intelligent Selection tools

• Numerous filter effects

• Many plug-ins, which enable easy addition of new file formats and new effect filters

• Support for custom brushes and patterns

I'll show you how to use a few of the Gimp's features here, to give you a taste of how the Gimp works.

Was the Gimp installed? Starting the Gimp Whether the Gimp was installed depends on the selections you made during installation of Red Hat Linux 6 from this book's CD. In addition, a menu item for the Gimp may—or may not—have been added to the Graphics menu-out of your Gnome main menu. If a menu item for the Gimp was created, choose that item to start the Gimp. You will be walked through a few final installation screens before the Gimp opens. If there is no menu item for the Gimp, use the File Manager to check whether a file named gimp is present in your /usr/bin directory. If it is, double-click it. This will complete the Gimp's installation and add a menu item for the Gimp to the Graphics menu for you to use the next time you want to start the Gimp. If there is no menu item for the Gimp and the gimp file is not present in /usr/bin, then the Gimp has probably not been installed. You can check this by running GnoRPM and seeing whether the Gimp package is present. It should be listed with the Multimedia packages in the Applications hierarchy. (For more information on GnoRPM, see Chapters 2 and 3.) If the Gimp is not listed in GnoRPM, they you will have to install it from the Red Hat Linux 6 CD as explained in Chapters 2 and 3. If all else falls, you can download the most recent version of the Gimp from http://www.gimp.org

To start the Gimp:

• With the Gnome desktop running, select the Gimp from the Graphics menu fly-out on the Gnome main menu. The Gimp toolbox will open (Figure 7.33).
  
  

  Figure 7.33. The Gimp's functionality can be accessed from its toolbox, which is what opens when you first start the Gimp, or by right-clicking an open image and using the fly-out menus.

  

  
  

  Tip

  If there is no menu item for the Gimp on the Graphics menu, see the previous sidebar "Was the Gimp Installed? Starting the Gimp" for instructions.

  Tip

  Most of the Gimp's functionality can be accessed by right-clicking and using fly-out menus with an image open in the Gimp.

Acquiring an image

Before you can really start working with the Gimp, you need an image to work on. There are many ways to obtain an image. You can start a new, empty file and use the Gimp's tools to add distinctiveness, or you can open an existing graphic file.

An interesting possibility is to start with a screen capture, or portion of your computer desktop.

To grab a screen capture:

1.	Make sure that the image you want to capture is open on your desktop; for example, in a Web browser.
2.	Choose Screen Tool from the Xtns menu in the Gimp toolbox. (Xtns is short for Extensions.) The Screen Shot dialog box will open (Figure 7.34).
3.	Make sure that Grab a Single Window is selected.
4.	Click OK. The Screen Shot dialog box will disappear from view, and a cross-hair cursor will appear.
5.	Click with the cross-hair cursor in the window you want to capture. Your selection will open, ready for editing, in a Gimp window (Figure 7.35). Figure 7.35. The window grabbed by the Screen Shot utility appears, ready for editing, in a Gimp window.

To crop an image:

1.	With an image open in a Gimp window, right-click anywhere in the image. The Gimp menu will open.
2.	Select Crop from the Tools menu fly-out (Figure 7.36). Figure 7.36. To crop an image in a Gimp window, select Crop from the Tools menu fly-out. A cross-hair cursor will appear on the image.
3.	Drag the cross-hair cursor to form the box that you want to crop out of the image. The perimeter of the area that you are selecting will be indicated with black box handles.
4.	Release the mouse. The Crop Information dialog box will appear (Figure 7.37). Figure 7.37. The area you are selecting to crop is indicated with perimeter handles; once you release the mouse, the Crop Information dialog box appears.
5.	Click Crop. The old (larger) image is replaced with the new, cropped image.

To apply a filter to an image:

1.	With an image open in a Gimp window, right-click anywhere in the image. The Gimp menu will open.
2.	Select Filters. The Filters fly-out menu will appear (Figure 7.38). Figure 7.38. The filter you select will be applied to the image in the Gimp window.
3.	Choose the filter effect you want The filter you selected will be applied to the image. Figure 7.39 shows the Glass Lens filter effect. Figure 7.39. You can choose from many filter effects, including the Glass Lens, which is shown.

To use Script-Fu to create a sphere:

1.	Select the Script-Fu fly-out menu from the Gimp Xtns menu.
2.	Select Sphere from the Misc fly-out menu. The Sphere Script-Fu Arguments dialog box will open (Figure 7.40). Figure 7.40. The Script-Fu Arguments dialog box is used to provide input parameters for a script.
3.	Enter the sphere's radius (in pixels), enter the lighting (in degrees), and select background and foreground color by clicking the appropriate buttons.
4.	Click OK. A sphere that matches the specifications you entered will open in a Gimp window (Figure 7.41). Figure 7.41. A sphere will open in a Gimp window that is based on your entries.