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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<th colspan="3" align="center" id="chaptername">3.2. Using the Channeldialog</th>
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<th width="60%" align="center" id="sectionname">3.2. Using the Channeldialog</th>
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<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id3335034"></a>3.2. Using the Channeldialog</h3>
</div>
</div>
</div>
<div class="variablelist">
<dl>
<dt>
<span class="term">Overview</span>
</dt>
<dd>
<p>
The top channels are the color channels and the optional Alpha
channel. They are always organized in the same order and they
cannot be erased. Selection masks are described below and
displayed as a list in the dialog. Every channel appears in
the list in form of a thumbnail. A right-click in a channel
thumbnail opens the <a href="ch04s03s03.html" title="3.3. Channels Menu">channel
menu</a>.
</p>
</dd>
<dt>
<span class="term">Channel attributes</span>
</dt>
<dd>
<p>
Every channel is shown in the list with its own attributes. The
main attribute is the name of the channel itself. You can edit
selection masks by double-clicking on their name. A
double_click on the thumbnail opens a full dialog where you can
also set the visual aspect of the channel in the image window.
In front of the thumbnail there is an eye icon:
<span class="guiicon">
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-eye.png" /></span>
</span>
by clicking on it you define whether the channel is visible or
not. As a result of this visibility, the view of the image
changes in the image window and a white image becomes yellow if
you remove the view of the blue because yellow is the
complementary color for blue. If you remove the view of the
Alpha channel, everything becomes transparent and nothing else
than a grey checkerboard is visible. The aspect of this virtual
background can be changed in the
<a href="ch04s18.html" title="18. Preferences">Preferences</a>.
The chain icon
<span class="guiicon">
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-vchain.png" /></span>
</span>
enables grouping of channels for operations on multiple channels.
</p>
<div class="caution" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Caution">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Caution]" src="../images/caution.png" />
</td>
<th align="left">Caution</th>
</tr>
<tr>
<td colspan="2" align="left" valign="top">
<p>
Activated channels appear highlighted in blue in the dialog.
If you click on a channel in the list you toggle activation
of the corresponding channel. Disabling a color channel red,
blue, or green has severe consequencies. For instance if you
disable the blue channel, all pixels from now on added to the
image will not have blue component, and so a white pixel will
have the yellow complementary color.
</p>
</td>
</tr>
</table>
</div>
</dd>
<dt>
<span class="term">Managing channels</span>
</dt>
<dd>
<p>
Under the channel list is a set of buttons allowing you to
perform some basic operations on channel list.
</p>
<p>
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-edit.png" /></span>
<a id="gimp-channel-edit"></a>
<span class="guilabel">Edit channel attributes</span>, only
available for selection masks. Here you can change the
<span class="guilabel">Channel name</span>. The other two
parameters affect channel is visibility in the image
window; they control <span class="guilabel">Opacity</span> and
color used for the mask in the image window. A click on
the color button displays the Gimp color selector and
then you can change the mask color.
</p>
</li>
<li>
<p>
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-new.png" /></span>
<a id="gimp-channel-new"></a>
<span class="guilabel">New channel</span>: you can create here a
new channel available to save a selection. Displayed
dialog lets you change <span class="guilabel">Opacity</span> and
mask color used in the image to represent the selection.
</p>
</li>
<li>
<p>
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-raise.png" /></span>
<a id="gimp-channel-raise"></a>
<span class="guilabel">Raise channel</span>, only available for
selection masks : you can here put the channel up a level
in the list. Press <span><b class="keycap">Shift</b></span> key to move
channel to top of the list.
</p>
</li>
<li>
<p>
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-lower.png" /></span>
<a id="gimp-channel-lower"></a>
<span class="guilabel">Lower channel</span>:
You can here put the channel down a level in the list.
Press the <span><b class="keycap">Shift</b></span> key to move the channel
to bottom of the list.
</p>
</li>
<li>
<p>
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-duplicate.png" /></span>
<a id="gimp-channel-duplicate"></a>
<span class="guilabel">Duplicate channel</span>: You can create
here a copy of the active channel. Name of new channel is
suffixed with a number.
</p>
<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>
You can also duplicate a color channel or the Alpha
channel. It's an easy way to keep a copy of them and to
use them later as a selection in an image.
</p>
</td>
</tr>
</table>
</div>
</li>
<li>
<p>
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-delete.png" /></span>
<a id="gimp-channel-selection-delete"></a>
<span class="guilabel">Delete channel</span>,only available for
selection masks: you can here delete the active channel.
</p>
</li>
<li>
<p>
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-selection.png" /></span>
<a id="gimp-channel-selection-replace"></a>
<span class="guilabel">Channel to selection</span>: here you can
transform the channel to become a selection. By default
the selection derived from a channel replaces any
previous active selection. It's possible to change this
by clicking on control keys.
</p>
<div class="itemizedlist">
<ul type="circle">
<li>
<p>
<a id="gimp-channel-selection-add"></a>
<span><b class="keycap">Shift</b></span>: the selection derived from a
channel is added to the previous active selection.
The final selection is merged from both.
</p>
</li>
<li>
<p>
<a id="gimp-channel-selection-subtract"></a>
<span><b class="keycap">Ctrl</b></span>: the final selection is the
substraction of selection derived from a channel from
the previously active one.
</p>
</li>
<li>
<p>
<a id="gimp-channel-selection-intersect"></a>
<span><b class="keycap">Shift Ctrl</b></span>: the final selection is
the intersection of selection derived from a channel
with the previously active one. Only common parts are
kept.
</p>
</li>
</ul>
</div>
<p>
</p>
</li>
</ul>
</div>
<p>
</p>
</dd>
</dl>
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