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//usr/share/doc/ImageMagick-6.2.8/www/Magick++/Pixels.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> <html> <head> <meta http-equiv="CONTENT-TYPE" content="text/html; charset=ibm437"> <title>Magick::Pixels Class</title> <meta name="GENERATOR" content="OpenOffice.org 1.0 (Win32)"> <meta name="AUTHOR" content="Bob Friesenhahn"> <meta name="CREATED" content="20020805;15302080"> <meta name="CHANGEDBY" content="Bob Friesenhahn"> <meta name="CHANGED" content="20020805;15341200"> <meta name="DESCRIPTION" content="Class to access raw image pixels."> <meta name="KEYWORDS" content="ImageMagick,Pixel,Magick++"> <style> <!-- TD P { color: #000000 } H1 { color: #000000 } P { color: #000000 } A:link { color: #0000ff } A:visited { color: #ff0000 } --> </style> </head> <body lang="en-US" text="#000000" link="#0000ff" vlink="#ff0000" bgcolor="#ffffff"> <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: 0cm;">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): <br> <br> </p> <table width="100%" border="0" cellpadding="2" cellspacing="2"> <tbody> <tr> <td> <p><font size="2"><font face="Courier New, Courier"><font color="#000099"> </font><font color="#ff0000">// Create base image</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> Image image(Geometry(254,218), "white");</font></font></font> </p> <p><font size="2"></font></p> <p> <font face="Courier New,Courier"><font color="#ff0000"><font size="-1"> // Set the image type to TrueColor DirectClass representation.</font></font></font><br> <font size="-1"><span style="color: rgb(0, 0, 153); font-family: courier new,courier,monospace;"> image.type(TrueColorType</span></font><font size="-1"><span style="color: rgb(0, 0, 153); font-family: courier new,courier,monospace;">);</span></font><br> </p> <p><font size="2"><font face="Courier New, Courier"> <font color="#ff0000">// Ensure that there is only one reference to underlying image</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#ff0000"> // If this is not done, then image pixels will not be modified.</font></font></font><br> <font size="2"><font face="Courier New, Courier"> <font color="#000099">image.modifyImage();<br> </font></font></font></p> <p><font size="2"><font face="Courier New, Courier"><font color="#000099"> </font><font color="#ff0000"> // Allocate pixel view</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> Pixels view(image);</font></font></font> </p> <p><font size="2"><font face="Courier New, Courier"><font color="#000099"> </font><font color="#ff0000"> // Set all pixels in region anchored at 38x36, with size 160x230 to green.</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> unsigned int columns = 196; unsigned int rows = 162;</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> Color green("green");</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> PixelPacket *pixels = view.get(38,36,columns,rows);</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> for ( int row = 0; row < rows ; ++row )</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> for ( int column = 0; column < columns ; ++column )</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> *pixels++=green;</font></font></font> </p> <p><font size="2"><font face="Courier New, Courier"><font color="#000099"> </font><font color="#ff0000"> // Save changes to image.<br> </font></font></font><font size="2"></font><font size="2"><font face="Courier New, Courier"><font color="#000099"> view.sync();</font></font></font> </p> <p><font size="2"><font face="Courier New, Courier"><font color="#000099"> </font><font color="#ff0000"> // Set all pixels in region anchored at 86x72, with size 108x67 to yellow.</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> columns = 108; rows = 67;</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> Color yellow("yellow");</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> pixels = view.get(86,72,columns,rows);</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> for ( int row = 0; row < rows ; ++row )</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> for ( int column = 0; column < columns ; ++column )</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> *pixels++=yellow;</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> view.sync();</font></font></font> </p> <p><font size="2"><font face="Courier New, Courier"><font color="#000099"> </font><font color="#ff0000"> // Set pixel at position 108,94 to red</font></font></font> <br> <font size="2"><font face="Courier New, Courier"><font color="#000099"> *(view.get(108,94,1,1)) = Color("red");</font></font></font> </p> <p><font size="2"><font face="Courier New, Courier"><font color="#000099"> </font><font color="#ff0000"> // Save changes to image.<br> </font></font></font><font size="2"><font face="Courier New, Courier"><font color="#000099"> view.sync();<br> <br> </font></font></font></p> </td> <td> <p><img src="Cache.png" name="Graphic1" align="bottom" width="254" height="218" border="0"></p> </td> </tr> </tbody> </table> <p style="margin-bottom: 0cm;"><i>Pixels</i> supports the following methods: <br> <br> </p> <p align="center" style="margin-bottom: 0cm;"><b>Pixel Cache Methods</b></p> <table width="100%" border="1" cellpadding="2" cellspacing="2"> <tbody> <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"></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"></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"></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. 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"></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"></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 <i>IndexPacket</i>, which is typedef <i>Quantum</i>, which is itself typedef <i>unsigned char</i>, or <i>unsigned short</i>, depending on the value of the <i>QuantumDepth </i>define) provide the <span lang="en-US">colormap</span> index (see <a href="Image.html#colorMap">colorMap</a>) for each pixel in the image. For CMYKA images, the indexes represent the black 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"></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"></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"></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"></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> </tbody> </table> <p><br> <br> </p> </body> </html>