User Guide

GNU Image Manipulation Program
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7.2.2 Creating a Free Selection
Figure 7.6: Using the Free Selection Tool
(a) A rather rough
selection
(b) Adding new selected areas to
an existing selection.
When using the lasso to select an object, some parts of the object and its proximity may be incorrectly either selected or not
selected. You can correct these defects by pressing the Shift or Ctrl keys while using the lasso. Here is how to do it: While
pressing Shift, draw the new border with the lasso and close the selection, including a part of the first selection. As soon as you
release the mouse button, both selections are added together. You could subtract the extra part of the first selection in a similar
way by pressing Ctrl.
Note
To correct selection defects precisely, use the Quick Mask.
7.3 QuickMask
Figure 7.7: Image with QuickMask enabled
The selection tools sometimes show their limits when they have to be used for creating a complex selection. In these cases, using
the QuickMask can make things much easier. Simply put, the QuickMask allows you to paint a selection instead of just tracing
its outline.
7.3.1 Overview
Normally when you create a selection in GIMP, you see it represented by the "marching ants" that trace along its outline. But
really there may be a lot more to a selection than the marching ants show you: in GIMP a selection is actually a full-fledged
grayscale channel, covering the image, with pixel values ranging from 0 (unselected) to 255 (fully selected). The marching ants
are drawn along a contour of half-selected pixels. Thus, what the marching ants show you as either inside or outside the boundary
is really just a slice through a continuum.
The QuickMask is GIMP’s way of showing you the full structure of the selection. Activating it also gives you the ability to
interact with the selection in new, and substantially more powerful, ways. To activate the QuickMask, click on the small red-
outlined button at the lower left of the image window. The button is a toggle, so clicking it again will return you to normal