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<title>4.2. QuickMask</title>
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<th colspan="3" align="center" id="chaptername">4.2. QuickMask</th>
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<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="gimp-image-window-qmask-button"></a>4.2. QuickMask</h3>
</div>
</div>
</div>
<a id="id3307631" class="indexterm"></a>
<div class="mediaobject">
<img src="../images/dialogs/dialogs-channel-quickmask.png" />
</div>
<p>
The <a href="ch03s02.html" title="2. Selection Tools">selection tools</a>
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.
</p>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3307770"></a>Overview</h4>
</div>
</div>
</div>
<p>
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 256 (fully selected). The marching ants
are drawn along a contour of half-selected pixels. Thus,
what the marching ants show you as either-or–inside or
outside the boundary–is really just a slice through a
continuum.
</p>
<p>
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
marching-ant mode. You can also activate the QuickMask by
selecting in the image
window menu
<span class="guimenu">Select</span>-><span class="guimenuitem">Toggle QuickMask</span>,
or by using
the <span><b class="keycap">Shift+Q</b></span> shortcut.
</p>
<p>
Activating the QuickMask shows you the selection as though
it were a translucent screen overlying the image, whose
transparency at each pixel indicates the degree to which
that pixel is selected. By default the mask is shown in
red, but you can change this if another mask color would
be more convenient. The less a pixel is selected, the
more it is obscured by the mask. Fully selected pixels
are shown completely clear.
</p>
<p>
When you are in QuickMask mode, many image manipulations
act on the selection channel rather than the image
itself. This includes, in particular, paint tools.
Painting with white causes the painted pixels to be
selected; painting with black causes them to be
unselected. You can use any of the paint tools, as well
as the bucket fill and gradient fill tools, in this way.
Advanced users of the Gimp learn that "painting the
selection" is the easiest and most effective way to
delicately manipulate it.
</p>
<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Tip">
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<img alt="[Tip]" src="../images/tip.png" />
</td>
<th align="left">Tip</th>
</tr>
<tr>
<td colspan="2" align="left" valign="top">
<p>
To save in a channel the selection done with the Quickmask
select in the image menu
<span class="guimenuitem">Select/Save to Channel</span>
</p>
</td>
</tr>
</table>
</div>
<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Tip]" src="../images/tip.png" />
</td>
<th align="left">Tip</th>
</tr>
<tr>
<td colspan="2" align="left" valign="top">
<p>
When QuickMask is active, Cut and Paste act on the
selection rather than the image. You can sometimes make
use of this as the most convenient way of transferring a
selection from one image to another.
</p>
</td>
</tr>
</table>
</div>
<p>
You can learn more on <a href="ch04s03s05.html" title="3.5. Quick Mask">Quickmask</a> and <a href="ch04s03s04.html" title="3.4. Selection masks">Selection masks</a> in
the section dedicated to the channel dialog.
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3308783"></a>Properties</h4>
</div>
</div>
</div>
<p>
There are two QuickMask properties you can change by
right-clicking on the QuickMask button.
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
Normally the QuickMask shows unselected areas "fogged
over" and selected areas "in clear", but you can reverse
this by choosing "Mask Selected Areas" instead of the
default "Mask Unselected Areas".
</p>
</li>
<li>
<p>
By choosing "Configure Color and Opacity", you can bring
up a dialog that allows you to set these to values other
than the defaults, which are red at 50% opacity.
</p>
</li>
</ul>
</div>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3308875"></a>Usage</h4>
</div>
</div>
</div>
<p></p>
<div class="procedure">
<ol type="1">
<li>
<p>
Open an image or begin a new document;
</p>
</li>
<li>
<p>
Activate the Quickmask using the left-bottom button in the
image window. If a selection is present the mask is
initialized with the content of the selection;
</p>
</li>
<li>
<p>
Choose any drawing tool and use it with greyscale colors on
the QuickMask;
</p>
</li>
<li>
<p>
Toggle off the Quickmask using the left-bottom button in
the image window;
</p>
</li>
</ol>
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