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<h3 class="title"><a id="plug-in-decompose"></a>3.16. Decompose</h3>
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<a id="id3359167" class="indexterm"></a>
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<h4 class="title"><a id="id3359044"></a>Overview</h4>
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<p>
This filter is found in
<span class="guimenuitem">Image>Filters/Colors/<span class="accel">D</span>ecompose</span>
</p>
<p>
This filter separates an image into its different components (RGB, HSV...).
</p>
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<div class="simplesect" lang="en" xml:lang="en">
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<h4 class="title"><a id="id3359499"></a>Options</h4>
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<div class="variablelist">
<dl>
<dt>
<span class="term">Decompose to Layers</span>
</dt>
<dd>
<p>
If this option is checked, greyscaled images will not be displayed straight away.
</p>
</dd>
<dt>
<span class="term">RGB Decomposing</span>
</dt>
<dd>
<p>
If the RGB radio button is clicked, a grey level image is created with three layers (Red, Green
and Blue), and two channels (Grey and Alpha).
</p>
<p>
This function is interesting when using Threshold tool. You can also perform operations like
cutting, pasting or moving selections in a single RBG channel. You can use an extracted
grayscale as a selection or mask by saving it in a channel (right-click>Select>Save to a
channel).
</p>
</dd>
<dt>
<span class="term">RGBA Decomposing</span>
</dt>
<dd>
<p>
If the RGBA radio button is clicked, a image is created similar at the RGB Decomposing
with a additional Alpha layer filled with the transparencies values of the source image.
The full translucent pixels are black and the full opaque pixels are white.
</p>
</dd>
<dt>
<span class="term">HSV Decomposing</span>
</dt>
<dd>
<p>
This option decomposes image into three greyscaled layers, one for Hue, one for Saturation
and another for Value.
</p>
<p>
Although <span class="guilabel">Hue</span> is greyscaled, it does represent hues. In color circle,
white and black are starting point and are superimposed. They represent Red color at top of
circle. Grey intermediate levels are corresponding to intermediate hues on circle: dark grey to
orange, mid grey to green and light grey to magenta.
</p>
<p>
<span class="guilabel">Saturation</span> and <span class="guilabel">Value</span>: White is maximum Saturation
(pure color) and maximum Value (very bright). Black is minimum Saturation (white) and minimum
Value (black).
</p>
</dd>
<dt>
<span class="term">CMY Decomposing</span>
</dt>
<dd>
<p>
This option decomposes image into three greyscaled layers, one for Yellow, one for Magenta
and another for Cyan.
</p>
<p>
This option might be useful to transfer image into printing softwares with CMY capabilities.
</p>
</dd>
<dt>
<span class="term">CMYK Decomposing </span>
</dt>
<dd>
<p>
This option is similar at the <span class="guilabel">CMY Decomposing</span> with a additonnal
layer for Black.
</p>
<p>
This option might be useful to transfer image into printing softwares with CMY capabilities.
</p>
</dd>
<dt>
<span class="term">Alpha Decomposing</span>
</dt>
<dd>
<p>
This option extracts the image transparency stored in the Alpha channel in
<a href="ch04s03.html" title="3. Channels dialog">Channel dialog</a>
in a separate image. The full translucent pixels are Black the full opaque
pixels are white. The graytones are smooth transitions of the transparency
in the source image.
</p>
</dd>
<dt>
<span class="term">LAB Decomposing</span>
</dt>
<dd>
<p>
This option decomposes image into three greyscaled layers, layer "L"
for Luminance, layer "A" for colors between green and red, layer "B"
for colors between blue and yellow.
</p>
<p>
The LAB Decomposing is a color model of the Luminance-Color family. A channel is
used for the Luminosity while two other channels are used for the Colors.
The LAB color model is used by Photoshop.
</p>
</dd>
<dt>
<span class="term">YCbCr Decomposing</span>
</dt>
<dd>
<p>
In Gimp there is four YCbCr decompositions with different values. Each option
decomposes image in three greyscaled layers, a layer for Luminance and two other
for blueness and redness.
</p>
<p>
The YCbCr color model also called YUV is now used for digital video (initially for
PAL analog video). It's based on the idea that the human eye is most sensitive to
luminosity, next to colors. The YCbCr Decomposing use a transformation matrix and
the different options are different values recommanded by ITU (International
Telecommunication Union) applied to the matrix .
</p>
</dd>
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