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<h2 class="title" style="clear: both"><a id="gimp-channel-dialog"></a>3. Channels dialog</h2>
</div>
</div>
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<a id="id3334487" class="indexterm"></a>
<div class="mediaobject">
<img src="../images/dialogs/dialogs-channel.png" />
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<p>
The Channels dialog is the main interface to edit, modify and manage
your channels. Channels have a double usage. This is why the dialog is
divided into two parts: the first part for color channels and the
second part for selection masks.
</p>
<p>
Color channels: Color channels apply to the image and not to a
specific layer. Basically, three primary colors are necessary to
render all the wide range of natural colors. As other digital
software, the<span class="acronym">Gimp</span> uses Red, Green, and Blue as
primary colors. The first and primary channels display the
<span class="guilabel">Red</span>, <span class="guilabel">Green</span>, and
<span class="guilabel">Blue</span> values of each pixel in your image. In front
of each channel is a thumbnail displaying a grayscale representation of
each channel, where white is 100% and black is 0% of the primary color.
Alternatively, if your image is not a colored but a Grayscale image,
there is only one primary channel called <span class="guilabel">Gray</span>. For
an Indexed image with a fixed number of known colors there is also only
one primary channel called <span class="guilabel">Indexed</span>. Then there is
a secondary optionnal channel called <span class="guilabel">Alpha</span>. This
channel displays transparency values of each pixel in your image. In
front of this channel is a thumbnail displaying a grayscale
representation of the transparency where white is opaque and visible,
and black is transparent and invisible. If you create your image
without transparency then the Alpha channel is not present, but you can
add it from the <a href="ch04s02.html" title="2. Layers dialog">Layers dialog
menu</a>. Also, if you have more than one layer in your image,
Gimp automatically creates an Alpha channel.
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<th align="left">Note</th>
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<p>
Gimp doesn't support CMYK or YUV color models.
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</p>
<p>
Representation of an image with channels:
</p>
<p>
<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-channels-example.png" /></span>
</p>
<p>
The right image is decomposed in
three color channels (red, green, and blue) and the Alpha channel for
transparency. On the right image the transparency is displayed as a
gray checkerboard. In the color channel white is always white because
all the colors are present and black is black. The red hat is visible
in the red channel but quite invisible in the other channels. This is
the same for plain green and blue which are visible only in their own
channels and invisible in others.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
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<h3 class="title"><a id="id3334485"></a>3.1. Calling the Dialog</h3>
</div>
</div>
</div>
<p>
The Channel dialog can be activated in many ways :
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
from the toolbox-menu:
<span class="guimenu">File</span>-><span class="guisubmenu">Dialogs</span>-><span class="guimenuitem">Channels</span>
</p>
</li>
<li>
<p>
from the image-menu:
<span class="guimenu">Dialogs</span>-><span class="guimenuitem">Channels</span>
</p>
</li>
<li>
<p>
from another dialog-menu:
<span class="guimenu">Add Tab</span>-><span class="guimenuitem">Channels</span>
</p>
</li>
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