The RRU GIMP Tutorial

Basic Menus & Key Concepts

for GIMP 1.0

[Main Toolbar] [Color types] [Opening images] [Saving images]
[Changing image types] [Layers] [Undo] [Preferences]
[Image Windows] [Image Window Menus]

Last updated: 10 September 1998

The Main Toolbar

The main toolbar consists of two pulldown menus, 21 basic tool icons, and the color selector. The pulldown menus are the File menu and Xtns (extensions) menu.

The File Menu

The File menu contains pretty much what you'd expect:

New	Create a new (empty) image in its own window
Open	Open an existing image in its own window
About...	"about" what you would expect...
Preferences...	Preferences editor
Tip of the day	Shows tips for using the GIMP
Dialogs ->	Allows access to various dialogs even if no images are currently open
Quit	Hasta la vista, baybee!

Note that there is no Save menu entry here. That's because the GIMP opens each image into a unique window, so Save will appear on a menu for a particular image. We'll get to that one later.

The Xtns (Extensions) Menu

The Xtns contains extensions to the base functionality of the GIMP, and tools to make using these extensions easier.

DB Browser	Browse the Procedutral database (PDB), a list of all functions available to plug-ins, script-fu, and so forth.
Screen Shot	Grabs an image of a single window or the whole screen.
Script-Fu ->	A Scheme-based language that lets you automate a series of GIMP operations to create more complex effects.
Web Browser ->	Interface to your web browser, with sub-menu entries for all the online doc sites, main GIMP sites, and so forth.

Other extensions are available as well. Check the GIMP site and the Plug-in Registry for details. (Extensions are implemented as a special sort of plug-in).

The icons cover the basic GIMP tools. All of these are also available in various menus, as well. The top 2 rows of icons designate various ways to select areas of an image, from the simple rectangular select to some fairly complex methods, such as the intelligent scissors.

The next row contains the familiar move, magnify and crop tools. After this are the transform tool (rotation, scaling, shearing and perspective), flip (horizontal and vertical), and text tools.

The final 3 rows contain various drawing tools - the color picker, flood fill, and blend; pencil, paintbrush and eraser; and airbrush, clone and convolver tools.

Some of these tools have option dialogs; double clicking on a tool pops up the tool dialog, as does selecting File->Dialogs->Tool Options . If the Options dialog is displayed, selecting another tool causes that tool's dialog to replace the current one. A couple of tools have dialogs that pop up when you actually try to use the tool; these are separate from the tools dialogs referenced here.

Color Selector

Finally we come to the color selector. This area shows the current background and foreground colors, with the foreground color on top. Selecting either of the color swatches pops up a very slick color selection dialog. Selecting the arrow swaps the foreground and background colors.

Selecting New pops up a dialog to set a few basic parameters for the new image. Width and height are (hopefully!) obvious. RGB is for color images, Grayscale is for monochrome (black, white and shades of gray) images.

Color Types

The GIMP knows about RGB images, grayscale images, and indexed images. With RGB images, each pixel (or point) on the image has a color associated with it made up of the Red, Green and Blue values for that pixel's color. Indexed images may also be color, but in this case each pixel's value is an index into a table of colors, known as a colormap. Grayscale images can be implemented in either of these fashions, but are treated as a special case of RGB, since that allows for far more flexibility in image manipulation.

Some GIMP operations work only on certain types of images; RGB is by far the best in most cases. This refers only to manipulating the image within the GIMP; the type of image you load or save is typically tied to a particular image type. In this case you simply convert image types after loading or before saving. This will be discussed under Changing Image Types.

The Fill type refers to the initial contents of the new image. The image may be filled with the current background color (white by default), white (for times when the current background color is something else) or it can be transparent.

Opening an image

Selecting Open results in a standard open dialog, with directories on the left and files on the right. You should generally be able to leave the file type determination set to Automatic, but if you have problems you can try using that menu to set a particular image type. This is handy when the image filename has the wrong, or no, extension.

Saving an image

So how do you save an image? Assuming you have one open (even a new, blank one), you position the mouse anywhere over the image window, and do whatever you normally do with a mouse to make a menu appear. On X, this is usually button 3, on Windows it's usually button 2, and on MacOS, you probably do something magic with the only button available and maybe a prayer.

This will pop up a menu with a number of items; the only one we care about right now is the File -> menu. Selecting this results in another menu with some of the same entries as the main File menu, and some extras, including Save and Save as... .

The GIMP tries to keep track of whether you have changed anything or not. If you have, the image is considered "dirty" or "unclean" (do I hear bells ringing?); otherwise the image is "clean". The action resulting from selecting Save depends on whether the image is clean or dirty. If it's clean (nothing has changed since you either loaded it or since your last Save), nothing happens. If it's dirty, the GIMP proceeds with the save process. Selecting Save as... will always initiate the save process.

The Save options dialog looks very much like the Load options dialog above. By default, if there is an extension on the file name, the GIMP tries to save the appropriate type of file (e.g., if the extension is ".jpg" or ".jpeg", it tries to write a JPEG file). You can also explicitly set a file type via the menu, changing "By extension" to the correct file type.

If you are unsure whether the file type you want works for the current image type, check that menu! It always lists all the file types the GIMP recognizes, but all file types not valid for the current image type will be grayed out. In this case, you need to cancel the save operation and change the image type. This will be covered soon, under Changing Image Types .

Dealing with Layers

If your image is at all complex, you have probably (perhaps unknowingly!) generated additional layers. Operations almost guaranteed to cause this include the text tool and Script-Fu. For standard image types, you will need to merge visible layers and/or flatten the image before you can save it. Otherwise, the save might fail, or worse yet, appear to succeed, but actually only save the current layer. Often this results in a blank image or an image with just text. It is almost never what you want.

Flattening will remove transparency.

If you really want to save all the layers separately (in case you want to work more on the image later), you can do this by choosing the XCF image type. This image type was developed specifically to save GIMP layers.

Both of these actions (Merge Visible Layers and Flatten Image) are available off the Layers menu, which is available from the main menu for a given image (via the MENU mouse button). You might also want to leave the Layers dialog up (at least until you get used to layers) to see the current layers. This dialog is available off the main "Files- Dialogs" menu, and off the images main menu via "Layers- Layers & Channels..."

Changing Image Types

There are several times you might want to change an image type.

To perform an operation requiring a particular image type.
To merge images of disparate types.
To save an image to a file type requiring a particular image type.

In any case, the sequence of events is the same. Position the mouse over the window of the image whose type you wish to change, press the mouse's MENU button, select the Image sub-menu, and then select one of the image types (the 3 menu items in the middle: RGB, Grayscale and Indexed). The current image type will be grayed out.

Selecting RGB or Grayscale quietly converts the image to that type. Selecting Indexed results in a dialog. If you select the "Generate Optimal Palette" option (the default), you can define the maximum number of colors to allow in the indexed image's colormap. You might want to play around with the dithering; most of the time you will want to leave this selected.

Undoing things

If you are unhappy with the result of changing the image type, or any other GIMP operation, simply undo it via the Edit->Undo menu item (MENU button over the image window) or by pressing CTRL-Z in the image window. This should work for any operation. The number of undo levels is defined in the Preferences panel; the default is 5.

Preferences

The GIMP comes with a fairly extensive preferences editor. Preferences can be applied just to the current session with the [OK] button, or saved permanently with the [Save] button. Even if you don't read through this section, you should glance at the Preferences panel.

Four sub-panels are available: Display, Interface, Environment, and Directories.

Image Windows

When you open an image, it appears in its own window. You can have as many windows open as you like (within the constraints of your hardware and operating system). Operations from the toolbar will affect whichever window has the GIMP focus at the moment.

Regardless of the number of image windows there will be only one toolbar per GIMP invocation. I do not recommend running multiple copies of the GIMP; it's easy to lose track of which toolbar affects which images.

The GIMP focus may be different than your window manager focus. If your window manager assigns focus by pointer traversal instead of pointer clicking, the GIMP focus will stay with the last window over which the pointer wasa clicked.

Image Window Menus

Image windows do not have menubars. They have drop down menus which appear when you select your pointer's Menu button (usually the rightmost button on multi-button, right-handed mice).

The File, Edit and Select menus handle the usual operations, plus a few others we'll cover later. The View menu covers zooming in and out, window information, and toggling of visible window features. The remaining menus actually handle the brunt of the GIMP's work for an individual image, and will be covered in a later section.

You can also configure and customize the GIMP.

Last updated: 10 September 1998

Miles O'Neal, <meo@rru.com>

11501 Johnson Rd / Leander, TX / 78641-5823