2. Selection Tools

2.1. Common Features

Selection tools are designed to select regions from images or layers so you can work on them without affecting the unselected areas. Each tool has its own individual properties, but the selection tools also share a number of options and features in common. These common features are described here; the variations are explained in the following sections for each tool specifically. If you need help with what a "selection" is in Gimp, and how it works, see Selection.

There are six selection tools:

  • Rectangle Select

  • Ellipse Select

  • Free Select (the Lasso)

  • Select Contiguous Regions (the Magic Wand)

  • Select by Color

  • Select Shapes from Image (Intelligent Scissors)

In some ways the Path tool can also be thought of as a selection tool: any closed path can be converted into a selection. It also can do a great deal more, though, and does not share the same set of options with the other selection tools.

Key modifiers (Defaults)

The behavior of selection tools is modified if you hold down the Ctrl, Shift, and/or Alt keys while you use them.

[Note] Note

Advanced users find the modifier keys very valuable, but novice users often find them confusing. Fortunately, it is possible for most purposes to use the Mode buttons (described below) instead of modifier keys.

Ctrl

Holding Ctrl while creating a selection can have as many as two effects simultaneously. The first effect is variable depending on which tool you are using: see the individual tool's documentation for this. The second effect, is common to all selection tools: it puts the tool into subtraction mode, so that the region you trace out is subtracted from the pre-existing selection. If you only want one of these actions to take place, you can release the Ctrl key prior to releasing the mouse button. Doing so will leave the selection in subtraction mode, but not perform the tool-specific action.

Alt

Holding Alt will allow movement of the current selection (only its frame, not its content). If the whole image is moved instead of the selection only, try Shift+Alt. Note that the Alt key is sometimes intercepted by the windowing system (meaning that Gimp never knows that it was pressed), so this may not work for everybody.

Shift

As with the Ctrl key, holding down Shift while creating a selection can have two distinct effects. The first varies according to which tool is used, but it generally involves constraining the tool in some way: for example, it constrains the rectangle-select tool to select a square region. The second effect is to change the selection mode to "addition", so that the region traced out is added to the pre-existing selection.If you require only one of these actions to take place, you can release the Shift key prior to releasing the mouse button. Doing so will leave the selection in addition mode, but without any constraints.

Ctrl+Shift

Using Ctrl-Shift together can do a variety of things, depending on which tool is used. Common to all selection tools is that the selection mode will be switched to intersection, so that after the operation is finished, the selection will consist of the intersection of the region traced out with the pre-existing selection. It is an exercise for the reader to play with the various combinations available when performing selections while holding Ctrl-Shift and releasing either both or either prior to releasing the mouse button.

Options

Here we describe the tool options that apply to all selection tools: options that apply only to some tools, or that affect each tool differently, are described in the sections devoted to the individual tools. The current settings for these options can be seen in the Tool Options dialog, which you should always have visible when you are using tools. (Most users keep it docked directly below the Toolbox.) To make the interface consistent, the same options are presented for all selection tools, even though some of them don't have any effect for some of the tools.

Mode

This determines the way that the selection you create is combined with any pre-existing selection. Note that the functions performed by these buttons can be duplicated using modifier keys, as described above. For the most part, advanced users use the modifier keys; novice users find the mode buttons easier.

Replace mode will cause any existing selection to be destroyed or replaced when the new selection is created.

Add mode will cause the new selection to be added to any existing selection regions.

Subtract mode will remove the new selection area from any existing selection regions.

Intersection mode will make a new selection from the area where the existing selection region and the new selection region overlap.

Antialiasing

This option only affects a few of the selection tools: it causes the boundary of the selection to be drawn more smoothly.

Feather Edges

This options allows the boundary of the selection to be blurred, so that points near the boundary are only partially selected. For further information regarding feathering, see the glossary entry Feathering.

Additional information

[Note] Note

When moving a selection beyond the boundaries of the image canvas, the selection will be cropped to the image area. Selections can exist on the visible canvas only. Selection movements and changes are, however, kept in the undo buffer should you need to repair an error.