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<h3 class="title"><a id="dialogs-selection-masks"></a>3.4. Selection masks</h3>
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<div class="mediaobject">
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<img src="../images/dialogs/dialogs-channel-masks.png" />
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Channels can be used to save and restore your selections. Clicking
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on the <span class="guilabel">Quick mask</span> button on the <a href="ch02s03s03.html" title="3.3. Image Window">Image window</a> automatically
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creates a new channel called <span class="guilabel">Qmask</span> and saves the
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displayed active selection to a thumbail in front of the
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channel.There are many selection tools in the Gimp like rectangular
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selection tool or fuzzy selection for continuous selections.
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Selection Masks are a graphical way to build selections into a gray
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level channel where white pixels are selected and black pixels are
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not selected. Therefore gray pixels are partially selected. You can
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think of them as feathering the selection, a smooth transition
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between selected and not selected. This is important to avoid the
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ugly pixelization effect when you fill the selection or when you
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erase its content after isolating a subject from background.
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<div class="variablelist">
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<span class="term">Creating Selection Masks</span>
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There are several ways to initialize a selection mask. From the
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<span class="guimenuitem"><span class="accel">S</span>elect</span>/
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<span class="guimenuitem">Save to <span class="accel">C</span>hannel</span> is
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available if there is an active selection. From the image window
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the bottom-left button creates a <a href="ch04s03s05.html" title="3.5. Quick Mask">Quick
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Mask</a>; the content will be initialized with the active
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selection. From the channel dialog, when you click on the
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<span class="guilabel">New channel</span> button or from the context menu.
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<div class="simplesect" lang="en" xml:lang="en">
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<div class="titlepage">
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<h4 class="title"><a id="id3334113"></a>Using Selectionmasks</h4>
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Once the channel is initialized, selected (highlighted in blue),
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visible (eye-icon in the dialog), and displayed as you want
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(color and opacity attributes), you can start to work with all
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the paint tools. The colors used are important. If you paint
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with some color other than white, grey, or black, the color Value
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(luminosity) will be used to define a gray (medium, light, or
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dark). When your mask is painted, you can transform it to a
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selection by clicking on the <span class="guilabel">Channel to
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selection</span> button or from the context menu.
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<th align="left">Tip</th>
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You can work in selection masks not only with the paint tool
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but also with other tools. For instance, you can use the
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selection tools to fill areas uniformly with gradients or
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patterns. By adding many selection masks in your list you can
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easily compose very complex selections. One can say that a
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selection mask is to a selection as a layer is to an image.
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<img alt="[Caution]" src="../images/caution.png" />
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<th align="left">Caution</th>
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<td colspan="2" align="left" valign="top">
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As long as a selection mask is activated you are working in the
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mask and not in the image. To work in the image you have to
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deactivate all selection masks. Don't forget also to stop
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displaying masks in the image by removing the eye icon. Check
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also that all RGB and Alpha channels are activated and
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displayed in the image.
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