In image processing, process either the whole image or only a specific section of it. GIMP needs to know to which area the following actions should be applied. Several selection tools help define a specific area. Once a selection has been made, it can be processed without affecting other parts of the image. Selection areas can also be increased or decreased in size with the aid of Shift (additive selection) and Ctrl (subtractive selection). The cursor changes to show a plus or a minus sign.

These functions are used to modify selections. Many functions are available, including crop, flip, and transform.

The paint tools represent pencil, paintbrush, airbrush, pen, and finger (smudge) and try to emulate their real-world properties on the PC.

Rectangular select is the simplest selection tool. By keeping the left mouse button pressed and dragging the mouse at the same time, mark a rectangular area. When you release the mouse button, a frame indicates the selected area. If you press Shift after you begin drawing the selection, only perfect squares can be selected.

This tool works like rectangular select, except it selects a circular or elliptical area. It is used in the same way, except pressing Shift after you begin selecting limits the selection to perfect circles.

This is the first usable selection tool for photographs. The lasso allows a free-hand selection of an irregular shape. Press the left mouse button and follow the shape as required. When you release the mouse button, the start point and end point are joined with a straight line. An accurate selection is difficult, so working with an enlarged image is recommended.

The magic wand fuzzy selection tool selects an image area through color similarity of adjacent pixels. If the default settings are not suitable, change the threshold value in the option box or combine several selections using Shift. The magic wand is ideal for selecting irregular areas of similar color.

With a bit of effort, the Bezier Curves tool allows you to capture specific areas or objects of an image. With the aid of anchor points set with mouse clicks, draw clean, curved lines. One advantage of this technique is that you can change the selection with the aid of control points. Once you have marked the area required, just click inside it to select it. This tool requires some practice to master, but is invaluable for more advanced work. Selections made with this tool can also be saved and manipulated with the ‘Paths’ tab of the Layers, Channels, and Paths dialog.

As you click, Intelligent Scissors tries to draw a selection along color or brightness edges. Sometimes it works quite well. Modify the settings in the option box.

When Move is activated, grab and move your selection with the mouse.

The magnifier is not a true transformation tool because it only zooms the screen representation in or out. The image itself is not changed. To use the zoom out function, which reduces the image on the screen by a certain percentage, press and hold Ctrl while clicking with the mouse.

For a true enlargement of your image, open the context menu with a right-click in your image and select ‘Image’ -> ‘Scale Image’. In the dialog box that opens, change the height and width of the image by percentages or by pixel values.

Use this tool to crop and resize your image. For an appealing impression for landscape photographs, for example, it is recommended to assign the sky one-third and the landscape two-thirds of the image height. Using the mouse, click and drag to open a rectangle. A click inside this rectangle crops the surrounding area. You can always undo this immediately with Ctrl + Z. You can also change the size of the rectangle. Resize the selection by grabbing and moving the top left or bottom right corners. Move the entire rectangle by grabbing and moving the bottom left or top right corners.

This icon hides a multitude of functionalities that might confuse a beginner. Process the whole image by clicking the tool icon first then the image or a portion by first making a selection then clicking the tool icon.

Four functions are available: rotate the image or the selection around an arbitrary rotation point, enlarge or reduce (Scaling), convert a rectangle into a trapezoid (Shearing), or distort the perspective of an area. The default setting is Rotation. Other functions can be specified in the option box opened by double-clicking the tool icon.

A simple tool that flips (mirrors) the selected area horizontally or vertically.

The T stands for text input. In GIMP, text input is done in two ways and many options are available. Double-click the tool to open the option box. By activating or deactivating ‘Use Dynamic Text’, select multiline text input with alignment or single line text input. A click in the image with the T tool activated opens the corresponding dialog box in which to enter text and select font, size, and other parameters.

GIMP provides a relatively simple text tool. Many text effects, such as shadows or gradients, must theoretically be input by hand. In practice, however, ‘Script-Fu’ and the ‘Filters’ submenu provide many automatic modification procedures, which have, in part, been specifically designed for use with text.

The color picker allows a controlled selection of a color from your image and transfers it to the color selection box. When you click a specific color in the image with the color picker tool, this color is selected. With it, quickly find, for example, a specific skin tone needed to retouch a photograph.

With the paint bucket, fill a selected area with color. Instead of a color, it can also fill with a pattern. Prior to the filling action, activate ‘Pattern Fill’. Everything in the selection is then painted over with the selected settings.

The icon represents a color or grayscale gradient. GIMP has several predefined gradients to use to fill the selected area. This tool is relatively complicated and requires some practice, especially if you want to overlay an image with transparent color gradients.

With the virtual pencil, as with a real pencil, draw free-hand lines. Select the type of line and the width and shape of the pencil point with the brush dialog. To access it, double-click the brush icon in the bottom right corner of the toolbox or select ‘File’ -> ‘Dialogs’ -> ‘Brushes’. Pencil points are available that do not actually exist in the real world. Make your pencil point extra-fine or extra-thick or select one of the special shapes.

The paintbrush draws with a softer, more liquid effect than the pencil. In the appropriate option box, set a fade out (the color intensity slowly diminishes while painting) or a gradient (selection via the gradient setting options). When the fade out option is activated, release the paintbrush and begin again to apply more color.

The eraser can both erase and unerase. The brush selection also sets the shape and size of the eraser.

The airbrush applies color like a real airbrush. Change the ‘Pressure’ and use the many different brush settings. This tool is ideal for use with a pressure-sensitive graphics tablet.

The clone tool (the icon represents a rubber stamp) is the ultimate instrument for photo retouching. It can be used to specify parts of images that are then cloned. In practice, this means that you specify very precisely which part of the image to copy where and in what form. This has relatively little to do with the ‘Cut’ and ‘Paste’ functions. It uses the paint functionality, allowing you to set the shape and opacity of your virtual rubber stamp.

Things become interesting, for example, if you have an old photograph with white stains. Activate the Clone tool and, if needed, its option box. Keep Shift held down and click the image area to use for the copy. Then release the mouse button and place the cursor on the damaged image area. If you now press the left mouse button and move the mouse, the image area marked in the first step of the procedure is inserted. When you move the mouse upwards, the area copied moves upwards, too. The point is marked by a crosshair. Depending on the brush settings, a small or a large radius is copied and, depending on the tool settings, copying is carried out in a translucent or opaque manner.

The Convolver tool (the icon shows a drop of water) is used for precise manual blurring or sharpening of image parts. Which of the two actions is active is set in the option box. The brush selection determines size and borders of the manipulation area. Blurring lays a kind of haze over the image or, as when using a drop of water on a water color painting, blurs the painted areas. Sharpening is the opposite. Here the program attempts to increase the contrast and make a neater separation of edges. Sharpening works well if you later look at your image from a distance. It also means a loss of information, however. Seen from very close up, the images look extremely pixellated.

The pen can be used for drawing and also for calligraphy. Writing well, however, can only be achieved with the aid of a graphics tablet. In the tool settings, adapt the shape of the pen to your own requirements.

The tool icon that looks like a pin is, in reality, a thin wooden stick with a glued-on opaque cardboard circle. Such an instrument is needed in a photographic laboratory for the perfect exposure of a manual paper copy. As only a small part of the negatives (or positives) is exposed perfectly, this instrument is moved over the areas that would otherwise become too dark while the paper is exposed. Thus, the exposure of specific problem areas can be adjusted individually. The opposite is a piece of cardboard with a little hole in it for postexposure. Both functions are fulfilled by this GIMP tool. Dodge (make lighter) individual image areas or burn (make darker) them. To create soft transitional borders, use a diffuse brush shape.

The finger shown in this tool icon moves over the color just applied to the paper and smudges it. This can be used to create very interesting effects.

With the calipers, measure distances and angles. In the associated option box, activate ‘Use Info Window’.