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<title>Magick::Pixels Class</title>
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<h1 align="center">Magick::Pixels</h1>
<p>The <i>Pixels</i> class provides efficient access to raw image
pixels. Image pixels (of type <a href=
"PixelPacket.html"><i>PixelPacket</i></a>) may be accessed directly
via the <i>Image Pixel Cache</i>. The image pixel cache is a
rectangular window (a view) into the actual image pixels (which may
be in memory, memory-mapped from a disk file, or entirely on disk).
Obtain existing image pixels via <i>get()</i>. Create a new pixel
region using <i>set().</i></p>
<p>Depending on the capabilities of the operating system, and the
relationship of the window to the image, the pixel cache may be a
copy of the pixels in the selected window, or it may be the actual
image pixels. In any case calling <i>sync()</i> insures that the
base image is updated with the contents of the modified pixel
cache. The method <i>decode()</i>supports copying foreign pixel
data formats into the pixel cache according to the
<i>QuantumTypes</i>. The method <i>encode()</i> supports copying
the pixels in the cache to a foreign pixel representation according
to the format specified by <i>QuantumTypes</i>.</p>
<p>Setting a view using the Pixels class does not cause the number
of references to the underlying image to be reduced to one.
Therefore, in order to ensure that only the current generation of
the image is modified, the Image's <a href=
"Image.html#modifyimage">modifyImage()</a> method should be invoked
to reduce the reference count on the underlying image to one. If
this is not done, then it is possible for a previous generation of
the image to be modified due to the use of reference counting when
copying or constructing an Image.</p>
<p>The <i>PixelPacket</i>* returned by the <i>set</i> and
<i>get</i> methods, and the <i>IndexPacket</i>* returned by the
<i>indexes</i> method point to pixel data managed by the
<i>Pixels</i> class. The <i>Pixels</i> class is responsible for
releasing resources associated with the pixel view. This means that
the pointer should never be passed to delete() or free().</p>
<p style="margin-bottom: 0in">The pixel view is a small image in
which the pixels may be accessed, addressed, and updated, as shown
in the following example, which produces an image similar to the
one on the right (minus lines and text):</p>
<table width="100%" border="0" cellpadding="2" cellspacing="2">
<tr>
<td>
<p><font color="#FF0000"><font face=
"Courier New, Courier"><font size="2">// Create base
image</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">Image image(Geometry(254,218),
"white");</font></font></font></p>
<p><font color="#FF0000"><font face=
"Courier New, Courier"><font size="2">// Set the image type to
TrueColor DirectClass representation.</font></font></font><br>
<font color="#000099"><font face=
"courier new, courier, monospace"><font size=
"2">image.type(TrueColorType);</font></font></font></p>
<p><font color="#FF0000"><font face=
"Courier New, Courier"><font size="2">// Ensure that there is only
one reference to underlying image</font></font></font><br>
<font color="#FF0000"><font face="Courier New, Courier"><font size=
"2">// If this is not done, then image pixels will not be
modified.</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">image.modifyImage();</font></font></font></p>
<p><font color="#FF0000"><font face=
"Courier New, Courier"><font size="2">// Allocate pixel
view</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">Pixels view(image);</font></font></font></p>
<p><font color="#FF0000"><font face=
"Courier New, Courier"><font size="2">// Set all pixels in region
anchored at 38x36, with size 160x230 to
green.</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">unsigned int columns = 196; unsigned int rows =
162;</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">Color green("green");</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">PixelPacket *pixels =
view.get(38,36,columns,rows);</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">for ( int row = 0; row &lt; rows ; ++row
)</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">for ( int column = 0; column &lt; columns ; ++column
)</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">*pixels++=green;</font></font></font></p>
<p><font color="#FF0000"><font face=
"Courier New, Courier"><font size="2">// Save changes to
image.<br></font></font></font> <font color="#000099"><font face=
"Courier New, Courier"><font size=
"2">view.sync();</font></font></font></p>
<p><font color="#FF0000"><font face=
"Courier New, Courier"><font size="2">// Set all pixels in region
anchored at 86x72, with size 108x67 to
yellow.</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">columns = 108; rows = 67;</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">Color yellow("yellow");</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">pixels = view.get(86,72,columns,rows);</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">for ( int row = 0; row &lt; rows ; ++row
)</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">for ( int column = 0; column &lt; columns ; ++column
)</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">*pixels++=yellow;</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">view.sync();</font></font></font></p>
<p><font color="#FF0000"><font face=
"Courier New, Courier"><font size="2">// Set pixel at position
108,94 to red</font></font></font><br>
<font color="#000099"><font face="Courier New, Courier"><font size=
"2">*(view.get(108,94,1,1)) = Color("red");</font></font></font>
&nbsp;</p>
<p><font color="#FF0000"><font face=
"Courier New, Courier"><font size="2">// Save changes to
image.<br></font></font></font> <font color="#000099"><font face=
"Courier New, Courier"><font size=
"2">view.sync();</font></font></font></p>
</td>
<td>
<p><a name="Graphic1" id="Graphic1"></a><img src="Cache.png" name=
"Graphic1" align="bottom" width="254" height="218" border="0" id=
"Graphic1"></p>
</td>
</tr>
</table>
<p style="margin-bottom: 0in"><i>Pixels</i> supports the following
methods:</p>
<p align="center" style="margin-bottom: 0in"><b>Pixel Cache
Methods</b></p>
<table width="100%" border="1" cellpadding="2" cellspacing="2">
<tr>
<td>
<p align="center"><b>Method</b></p>
</td>
<td>
<p align="center"><b>Returns</b></p>
</td>
<td>
<p align="center"><b>Signature</b></p>
</td>
<td>
<p align="center"><b>Description</b></p>
</td>
</tr>
<tr>
<td>
<p align="center"><a name="get" id="get"></a><font size=
"2">get</font></p>
</td>
<td>
<p><font size="2"><a href=
"PixelPacket.html">PixelPacket</a>*</font></p>
</td>
<td>
<p><font size="2">const int x_, const int y_, const unsigned const
int columns_, const unsigned int rows_</font></p>
</td>
<td>
<p><font size="2">Transfers read-write pixels from the image to the
pixel cache as defined by the specified rectangular region.
Modified pixels may be subsequently transferred back to the image
via <i>sync</i>. The value returned is intended for pixel access
only. It should never be deallocated.</font></p>
</td>
</tr>
<tr>
<td>
<p align="center"><a name="getConst" id="getConst"></a><font size=
"2">getConst</font></p>
</td>
<td>
<p><font size="2">const <a href=
"PixelPacket.html">PixelPacket</a>*</font></p>
</td>
<td>
<p><font size="2">const int x_, const int y_, const unsigned int
columns_, const unsigned int rows_</font></p>
</td>
<td>
<p><font size="2">Transfers read-only pixels from the image to the
pixel cache as defined by the specified rectangular
region.</font></p>
</td>
</tr>
<tr>
<td>
<p align="center"><a name="set" id="set"></a><font size=
"2">set</font></p>
</td>
<td>
<p><font size="2"><a href=
"PixelPacket.html">PixelPacket</a>*</font></p>
</td>
<td>
<p><font size="2">const int x_, const int y_, const unsigned int
columns_, const unsigned int rows_</font></p>
</td>
<td>
<p><font size="2">Allocates a pixel cache region to store image
pixels as defined by the region rectangle. &nbsp; This area is
subsequently transferred from the pixel cache to the image via
<i>sync</i>. The value returned is intended for pixel access only.
It should never be deallocated.</font></p>
</td>
</tr>
<tr>
<td>
<p align="center"><a name="sync" id="sync"></a><font size=
"2">sync</font></p>
</td>
<td>
<p><font size="2">void</font></p>
</td>
<td>
<p><font size="2">void</font></p>
</td>
<td>
<p><font size="2">Transfers the image cache pixels to the
image.</font></p>
</td>
</tr>
<tr>
<td>
<p align="center"><a name="indexes" id="indexes"></a><font size=
"2">indexes</font></p>
</td>
<td>
<p><font size="2">IndexPacket*</font></p>
</td>
<td>
<p><font size="2">void</font></p>
</td>
<td>
<p><font size="2">Returns the PsuedoColor pixel indexes
corresponding to the pixel region defined by the last <a href=
"#get">get</a> , <a href="#getConst">getConst</a>, or <a href=
"#set">set</a> call. Only valid for PseudoColor and CMYKA images.
The pixel indexes (an array of type</font> <font size=
"2"><i>IndexPacket</i></font><font size="2">, which is
typedef</font> <font size="2"><i>Quantum</i></font><font size="2">,
which is itself typedef</font> <font size="2"><i>unsigned
char</i></font><font size="2">, or</font> <font size=
"2"><i>unsigned short</i></font><font size="2">, depending on the
value of the</font> <font size="2"><i>QuantumDepth</i></font>
<font size="2">define) provide the</font> <font size=
"2"><span lang="en-US">colormap</span></font> <font size="2">index
(see <a href="Image.html#colormap">colorMap</a>) for each pixel in
the image. For CMYKA images, the indexes represent the matte
(alpha) channel. The value returned is intended for pixel access
only. It should never be deallocated.</font></p>
</td>
</tr>
<tr>
<td>
<p align="center"><a name="x" id="x"></a><font size=
"2">x</font></p>
</td>
<td>
<p><font size="2">int</font></p>
</td>
<td>
<p><font size="2">void</font></p>
</td>
<td>
<p><font size="2">Left ordinate of view</font></p>
</td>
</tr>
<tr>
<td>
<p align="center"><a name="y" id="y"></a><font size=
"2">y</font></p>
</td>
<td>
<p><font size="2">int</font></p>
</td>
<td>
<p><font size="2">void</font></p>
</td>
<td>
<p><font size="2">Top ordinate of view</font></p>
</td>
</tr>
<tr>
<td>
<p align="center"><a name="columns" id="columns"></a><font size=
"2">columns</font></p>
</td>
<td>
<p><font size="2">unsigned int</font></p>
</td>
<td>
<p><font size="2">void</font></p>
</td>
<td>
<p><font size="2">Width of view</font></p>
</td>
</tr>
<tr>
<td>
<p align="center"><a name="rows" id="rows"></a><font size=
"2">rows</font></p>
</td>
<td>
<p><font size="2">unsigned int</font></p>
</td>
<td>
<p><font size="2">void</font></p>
</td>
<td>
<p><font size="2">Height of view</font></p>
</td>
</tr>
</table>
<p><br>
<br></p>
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