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<div class="document" id="magick-pixelpacket-structure">
<h1 class="title">Magick::PixelPacket Structure</h1>
<!-- -*- mode: rst -*- -->
<!-- This text is in reStucturedText format, so it may look a bit odd. -->
<!-- See http://docutils.sourceforge.net/rst.html for details. -->
<p>The PixelPacket structure is used to represent DirectClass pixels in
GraphicsMagick. GraphicsMagick may be compiled to support 32, 64, or
even 128 bit pixels. The size of PixelPacket is controlled by the
value of the QuantumDepth define. The default build depth is 32 bit
pixels, which provides minumum ("web standard") accuracy, least memory
consumption, and best performance. If deeper images need to be
supported or more mathematical accuracy is desired, then
GraphicsMagick may be compiled with QuantumDepth=16 or
QuantumDepth=32.</p>
<p>The following table shows the relationship between QuantumDepth, the
type of Quantum, and the overall PixelPacket size:</p>
<table border="1" class="docutils">
<caption>Effect Of QuantumDepth Values</caption>
<colgroup>
<col width="28%" />
<col width="35%" />
<col width="37%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">QuantumDepth</th>
<th class="head">Quantum Type</th>
<th class="head">PixelPacket Size</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>8</td>
<td>unsigned char</td>
<td>32 bits</td>
</tr>
<tr><td>16</td>
<td>unsigned short</td>
<td>64 bits</td>
</tr>
<tr><td>32</td>
<td>unsigned int</td>
<td>128 bits</td>
</tr>
</tbody>
</table>
<p>The members of the PixelPacket structure, and their interpretation,
are shown in the following table:</p>
<table border="1" class="docutils">
<caption>PixelPacket Structure Members</caption>
<colgroup>
<col width="10%" />
<col width="10%" />
<col width="19%" />
<col width="31%" />
<col width="28%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Member</th>
<th class="head">Type</th>
<th class="head" colspan="3">Interpretation</th>
</tr>
<tr><th class="head"></th>
<th class="head"> </th>
<th class="head">RGBColorspace</th>
<th class="head">RGBColorspace + matte</th>
<th class="head">CMYKColorspace</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>red</td>
<td>Quantum</td>
<td>Red</td>
<td>Red</td>
<td>Cyan</td>
</tr>
<tr><td>green</td>
<td>Quantum</td>
<td>Green</td>
<td>Green</td>
<td>Magenta</td>
</tr>
<tr><td>blue</td>
<td>Quantum</td>
<td>Blue</td>
<td>Blue</td>
<td>Yellow</td>
</tr>
<tr><td>opacity</td>
<td>Quantum</td>
<td>Ignored</td>
<td>Opacity</td>
<td>Black</td>
</tr>
</tbody>
</table>
<p>Note that opacity is stored inverted from most other software
(i.e. maximum value is completely transparent and minum value is
totally opaque).</p>
<p>Note that for CMYKColorspace + matte (CMYKA), the opacity is stored in
the assocated IndexPacket.</p>
<p>Copyright © Bob Friesenhahn 1999 - 2018</p>
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