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.
2.1.1. 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
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.
Space bar
Pressing the Space Bar while using a selection
tool transforms this tool into Move tool as long as you press
the bar.
2.1.2. 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.
Výsledkem použití režimu průnik je výběr pouze v oblastech, kde se
starý a nový výběr překrývají.
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.
2.1.3. Additional information
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.
![[Note]](../images/note.png)
