Image Editing Using GIMP

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GIMP is an extremely powerful image editor that offers the kind of functions usually associated with top-end software like Adobe Photoshop. Although GIMP is not aimed at beginners, those new to image editing can get a lot from it, provided they put in a little work.

The program relies on a few unusual concepts within its interface, which can catch many people off guard. The first of these is that each of the windows within the program, such as floating dialog boxes or palettes, gets its own panel entry. In other words, the GIMP's icon bar, image window, settings window, and so on have their own buttons on the Ubuntu desktop panel alongside your other programs, as if they were separate programs.

■Note GIMP's way of working is referred to as a Single Document Interface, or SDI. It's favored by a handful of programs that run under Linux and seems to be especially popular among programs that let you create things.

Because of the way that GIMP runs, before you start up the program, it's a wise idea to switch to a different virtual desktop (virtual desktops are discussed in Chapter 7), which you can then dedicate entirely to GIMP.

Click Applications > Graphics > GNU Image Manipulation Program to run GIMP. You'll be greeted by what appears to be a complex assortment of program windows.

Now you need to be aware of a second unusual aspect of the program: its reliance on right-clicking. Whereas right-clicking usually brings up a context menu offering a handful of options, within GIMP, it's the principal way of accessing the program's functions. Right-clicking an image brings up a menu offering access to virtually everything you'll need while editing. Ubuntu includes the latest version of GIMP, 2.4, and this features a menu bar in the main image-editing window. This is considered sacrilege by many traditional GIMP users, although it's undoubtedly useful for beginners. However, the right-click menu remains the most efficient way of accessing GIMP's tools.

The main toolbar window, shown in Figure 20-3, is on the left. This can be considered the heart of GIMP, because when you close it, all the other program windows are closed, too. The menu bar on the toolbar window offers most of the options you're likely to use to start out with GIMP. For example, File > Open will open a browser dialog box in which you can select files to open in GIMP. It's even possible to create new artwork from scratch by choosing File > New.

■Tip To create vector artwork, a better choice is a program like Inkscape (, which can be downloaded via Synaptic Package Manager (to learn about software installation, see Chapter 28).

Beneath the menu bar in the main toolbar window are the tools for working with images. Their functions are described in Table 20-1, which lists the tools in order from left to right, starting at the top left.

Foreground and Background Colors

Save Current Tool Options -

Foreground and Background Colors

Save Current Tool Options -

Image-Editing Tools

Tool Options

Image-Editing Tools

Tool Options

Load Saved Tool Options Figure 20-3. GIMP's main toolbar window

Revert to Default Tool Settings Delete Saved Tool Options

Table 20-1. GIMP Image-Editing Tools


Description of Use

Rectangle Select Click and drag to select a rectangular area within the image. This selected area can then be copied and pasted into a different part of the image or turned into a new layer.

Ellipse Select Create an oval or circular selection area within the image, which you can then copy and paste.

Free Select Click and draw with the mouse to create a hand-drawn selection area.

Your selection should end where it started. If not, GIMP will draw a straight line between the start and end of the selection.

Table 20-1. GIMP Image-Editing Tools (Continued)


Description of Use

Fuzzy Select

Select by Color

Scissors Select

Foreground Select


Color Picker



Known as the "magic wand" in other image editors, this tool creates a selection area based on the color of the pixels where you click. For example, clicking a red car hood will select most, if not all of the hood, because it is mostly red.

Works like the Fuzzy Select tool, but will create a selection across the entire image based on the color you select. In other words, selecting a black T-shirt will also select a black signpost elsewhere in the picture if the hues are similar.

Another "magical" tool that lets you create a selection by clicking on various points within an image, with the program joining the points together based on the color differences between the two points. This means that you can select the outline of a car by clicking a few points around the edge of the car and, provided the color of the car is different from the background, GIMP will work out the color differences and select the car's shape automatically.

Lets you automatically create an intricate selection of an object in the foreground of a picture, via a three-step process. Click to draw roughly around the foreground object as with the Free Select tool. (Be careful you don't stray into the object; if you do, momentarily select a different tool, which will cancel the selection, and try again.) Then release the mouse button and draw across the main areas of the object using a kind of paintbrush tool. For example, if the object is a face, draw a little on the skin and hair. The trick is to cover areas that have different color ranges, because that's how GIMP detects the edges. You'll see that the background—the area that won't be selected—is masked out in blue tint. If any of the foreground object is masked, draw on it to add it to the selection area. You can subtract from the selection area by Ctrl-clicking. Once you're happy with the selection, hit Enter.

Draws Bezier curves in order to create paths, which are akin to selections and can be saved for use later on in the image-editing process. Just click and drag to draw a curve. Each extra click you make will define a new curve, which will be joined to the last one. To turn the path into a selection, click the button at the bottom of the toolbar.

Lets you see the RGB, HSV, or CMYK values of any color within the image. Simply click the mouse within the image.

Click to zoom into the image, right-click to see various zoom options, and hold down the Alt key while clicking to zoom out.

Measures distances between two points (in pixels) and also angles. Just click and drag to use it. The measurements will appear at the bottom of the image window.


Click and drag to move any selection areas within the image, as well as rearrange the positioning of various layers.

Table 20-1. GIMP Image-Editing Tools (Continued)


Description of Use


Crop Rotate

Scale Shear




Bucket Fill






Allows you to align layers to other objects relative to each other. To choose a layer, click an object within the preferred layer. To select several layers, Shift-click objects inside the preferred layers. In the tool options of the Alignment tool, select how the layer or layers will be aligned relative to other layers or image objects. Alignment includes left, center horizontal, right, top, center vertical, and bottom, with an option to use offsets as well.

Click and drag to define an area of the image to be cropped. Anything outside the selection area you create will be discarded.

Rotates any selections you make and can also rotate entire layers. It opens a dialog box in which you can set the rotation manually. Alternatively, you can simply click and drag the handles behind the dialog box to rotate by hand.

Known in some other image editors as "transform," lets you resize the selection area or layer. It presents a dialog box where you can enter numeric values, or you can click and drag the handles to resize by hand.

Lets you transform the image by shearing it. Slant a selection by clicking and dragging the corners of the selection area (if the selection area isn't square, a rectangular grid will be applied to it for the purposes of transformation).

Lets you transform a selection by clicking and dragging its four corners and independently moving them without affecting the other corners. In this way, a sense of perspective can be emulated.

Flips a selection or image so that it is reversed on itself, either horizontally (click) or vertically (Ctrl-click).

Click the image to add text.

Fills a particular area with solid color or pattern, according to the color or pattern selected in the color box or fill type box below.

Creates a gradient fill based on the foreground and background colors. Just click and drag to add the fill.

Lets you draw individual pixels when zoomed in, or hard-edge lines when zoomed out. Simply click and drag to draw freehand, and hold down Shift to draw lines between two points.

Lets you draw on the picture in a variety of brush styles to create artistic effects. A brush can also be created from an image, allowing for greater versatility.

Rather like the Paintbrush tool in reverse, deletes whatever is underneath the cursor. If layers are being used, the contents of the layer beneath will become visible.

Like the Paintbrush tool, in that it draws on the picture in a variety of styles. However, the density of the color depends on the length of time you press the mouse button. Tap the mouse button, and only a light color will appear. Press and hold the mouse button, and the color will become more saturated.

Table 20-1. GIMP Image-Editing Tools (Continued)


Description of Use



Perspective Clone


Smudge Dodge/Burn

Like the Paintbrush tool, except that, rather like an ink pen, the faster you draw, the thinner the brushstroke.

Allows you to copy one part of an image to another via a brush. The origin point is defined by Ctrl-clicking.

Typically used to remove unwanted irregularities, such as pimples, scars, and blemishes in a person's face. Ctrl-click an ideal source similar to the area that needs to be healed, and then draw over the blemish, which will disappear. Effectively, the Healing tool is a Clone tool that has some intelligence built in to aid intermixing of the sample area and the area you're drawing over.

Similar to the Clone tool, but also allows you to take into account perspective within the picture. For example, you might want to clone a person standing in the foreground of a picture so she appears to be standing near a tree at the back of a photo. She should be smaller because of perspective, which you can accomplish with this tool. Click and drag the perspective bars at the corners of the image to roughly match the perspective within the picture (the depth), click the Perspective Clone tool, and Ctrl-click to select the area you want to clone. Then draw where you want the cloned material to appear.

Clicking and drawing on the image will spot blur or sharpen the image, depending on the settings in the tool options area, in the lower half of the toolbar.

As its name suggests, clicking and drawing with this tool will smudge the image, rather like rubbing a still-wet painting with your finger.

Lets you spot lighten and darken an image by clicking and drawing on the image. The results depend on the settings in the tool options part of the window.

Directly beneath the image-editing tool icons, on the left, is an icon that shows the foreground and background colors that will be used when drawing with tools such as the Paintbrush. To define a new color, double-click either the foreground (top) or background (bottom) color box.

Beneath these icons, you'll see the various options for the selected tool. The brush selector lets you choose the thickness of the brushstrokes and patterns that are used with various tools. Simply click each to change them. By using the buttons at the bottom of the window, you can save the current tool options, load tool options, and delete a previously saved set of tool options. Clicking the button on the bottom right lets you revert to the default settings for the tool currently being used (useful if you tweak too many settings!).

Next to the toolbar window is the Layers dialog box. You can close this if you wish, and reopen it later by selecting Dialogs > Layers.

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