1<?xml version="1.0" encoding="utf-8" ?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 4<head> 5<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 6<title>Magick++ API: Working with Pixels </title> 7<link rel="stylesheet" href="magick.css" type="text/css" /> 8</head> 9<body> 10<div class="doc-section"> 11<h1 align="center">Magick::Pixels</h1> 12<p>The <i>Pixels</i> class provides efficient access to raw image 13pixels. Image pixels (of type <a href="PixelPacket.html"><i>PixelPacket</i></a>) 14may be accessed directly via the <i>Image Pixel Cache</i>. The image 15pixel cache is a rectangular window (a view) into the actual image 16pixels (which may be in memory, memory-mapped from a disk file, or 17entirely on disk). Obtain existing image pixels via <i>get()</i>. 18Create a new pixel region using <i>set().</i> </p> 19<p>Depending on the capabilities of the operating system, and the 20relationship of the window to the image, the pixel cache may be a copy 21of the pixels in the selected window, or it may be the actual image 22pixels. In any case calling <i>sync()</i> insures that the base image 23is updated with the contents of the modified pixel cache. The method <i>decode()</i>supports 24copying foreign pixel data formats into the pixel cache according to 25the <i>QuantumTypes</i>. The method <i>encode()</i> supports copying 26the pixels in the cache to a foreign pixel representation according to 27the format specified by <i>QuantumTypes</i>. </p> 28<p>Setting a view using the Pixels class does not cause the number of 29references to the underlying image to be reduced to one. Therefore, in 30order to ensure that only the current generation of the image is 31modified, the Image's <a href="Image++.html#modifyImage">modifyImage()</a> 32method should be invoked to reduce the reference count on the underlying 33image to one. If this is not done, then it is possible for a previous 34generation of the image to be modified due to the use of reference 35counting when copying or constructing an Image. </p> 36<p>The <i>PixelPacket</i>* returned by the <i>set</i> and <i>get</i> 37methods, and the <i>IndexPacket</i>* returned by the <i>indexes</i> 38method point to pixel data managed by the <i>Pixels</i> class. The <i>Pixels</i> 39class is responsible for releasing resources associated with the pixel 40view. This means that the pointer should never be passed to delete() or 41free(). </p> 42<p style="margin-bottom: 0cm;">The pixel view is a small image in which 43the pixels may be accessed, addressed, and updated, as shown in the 44following example, which produces an image similar to the one on the 45right (minus lines and text): </p> 46<p class="image"><img class="icon" src="Cache.png" name="Graphic1" align="bottom" width="254" border="0" /></p> 47<div class="viewport"> 48 // Create base image 49 Image image(Geometry(254,218), "white"); 50 51 52 // Set the image type to TrueColor DirectClass representation. 53 image.type(TrueColorType); 54 // Ensure that there is only one reference to underlying image 55 // If this is not done, then image pixels will not be modified. 56 image.modifyImage(); 57 58 // Allocate pixel view 59 Pixels view(image); 60 61 // Set all pixels in region anchored at 38x36, with size 160x230 to green. 62 size_t columns = 196; size_t rows = 162; 63 Color green("green"); 64 PixelPacket *pixels = view.get(38,36,columns,rows); 65 for ( ssize_t row = 0; row < rows ; ++row ) 66 for ( ssize_t column = 0; column < columns ; ++column ) 67 *pixels++=green; 68 69 // Save changes to image. 70 view.sync(); 71 72 // Set all pixels in region anchored at 86x72, with size 108x67 to yellow. 73 columns = 108; rows = 67; 74 Color yellow("yellow"); 75 pixels = view.get(86,72,columns,rows); 76 for ( ssize_t row = 0; row < rows ; ++row ) 77 for ( ssize_t column = 0; column < columns ; ++column ) 78 *pixels++=yellow; 79 view.sync(); 80 81 // Set pixel at position 108,94 to red 82 *(view.get(108,94,1,1)) = Color("red"); 83 84 // Save changes to image. 85 view.sync(); 86</div> 87<p style="margin-bottom: 0cm;"><i>Pixels</i> supports the following 88methods: </p> 89<p align="center" style="margin-bottom: 0cm;"><b>Pixel Cache Methods</b></p> 90<table width="100%" border="1" cellpadding="2" cellspacing="2"> 91 <tbody> 92 <tr> 93 <td> 94 <p align="center"><b>Method</b></p> 95 </td> 96 <td> 97 <p align="center"><b>Returns</b></p> 98 </td> 99 <td> 100 <p align="center"><b>Signature</b></p> 101 </td> 102 <td> 103 <p align="center"><b>Description</b></p> 104 </td> 105 </tr> 106 <tr> 107 <td> 108 <p align="center"><a name="get"></a><font size="2">get</font></p> 109 </td> 110 <td> 111 <p><font size="2"><a href="PixelPacket.html">PixelPacket</a>*</font></p> 112 </td> 113 <td> 114 <p><font size="2">const ssize_t x_, const ssize_t y_, const size_t 115columns_, const size_t rows_</font></p> 116 </td> 117 <td> 118 <p><font size="2">Transfers read-write pixels from the image to 119the pixel cache as defined by the specified rectangular region. 120 Modified pixels may be subsequently transferred back to the image 121 via <i>sync</i>. The value returned is intended for pixel access 122 only. It should never be deallocated.</font></p> 123 </td> 124 </tr> 125 <tr> 126 <td> 127 <p align="center"><a name="getConst"></a><font size="2">getConst</font></p> 128 </td> 129 <td> 130 <p><font size="2">const <a href="PixelPacket.html">PixelPacket</a>*</font></p> 131 </td> 132 <td> 133 <p><font size="2">const ssize_t x_, const ssize_t y_, const size_t 134 columns_, const size_t rows_</font></p> 135 </td> 136 <td> 137 <p><font size="2">Transfers read-only pixels from the image to 138the pixel cache as defined by the specified rectangular region.</font></p> 139 </td> 140 </tr> 141 <tr> 142 <td> 143 <p align="center"><a name="set"></a><font size="2">set</font></p> 144 </td> 145 <td> 146 <p><font size="2"><a href="PixelPacket.html">PixelPacket</a>*</font></p> 147 </td> 148 <td> 149 <p><font size="2">const ssize_t x_, const ssize_t y_, const size_t 150 columns_, const size_t rows_</font></p> 151 </td> 152 <td> 153 <p><font size="2">Allocates a pixel cache region to store image 154 pixels as defined by the region rectangle. This area is 155 subsequently transferred from the pixel cache to the image via <i>sync</i>. 156The value returned is intended for pixel access only. It should 157never be deallocated.</font></p> 158 </td> 159 </tr> 160 <tr> 161 <td> 162 <p align="center"><a name="sync"></a><font size="2">sync</font></p> 163 </td> 164 <td> 165 <p><font size="2">void</font></p> 166 </td> 167 <td> 168 <p><font size="2">void</font></p> 169 </td> 170 <td> 171 <p><font size="2">Transfers the image cache pixels to the image.</font></p> 172 </td> 173 </tr> 174 <tr> 175 <td> 176 <p align="center"><a name="indexes"></a><font size="2">indexes</font></p> 177 </td> 178 <td> 179 <p><font size="2">IndexPacket*</font></p> 180 </td> 181 <td> 182 <p><font size="2">void</font></p> 183 </td> 184 <td> 185 <p><font size="2">Returns the PsuedoColor pixel indexes 186 corresponding to the pixel region defined by the last <a href="Pixels.html#get">get</a> 187 , <a href="Pixels.html#getConst">getConst</a>, or <a href="Pixels.html#set">set</a> 188 call. Only valid for PseudoColor and CMYKA images. The pixel 189 indexes (an array of type <i>IndexPacket</i>, which is typedef <i>Quantum</i>, 190which is itself typedef <i>unsigned char</i>, or <i>unsigned short</i>, 191depending on the value of the <i>QuantumDepth </i>define) provide 192the <span lang="en-US">colormap</span> index (see <a 193 href="Image++.html#colorMap">colorMap</a>) for each pixel in the 194image. For CMYKA images, the indexes represent the black 195channel. The value returned is intended for pixel access only. It 196should never be deallocated.</font></p> 197 </td> 198 </tr> 199 <tr> 200 <td> 201 <p align="center"><a name="x"></a><font size="2">x</font></p> 202 </td> 203 <td> 204 <p><font size="2">int</font></p> 205 </td> 206 <td> 207 <p><font size="2">void</font></p> 208 </td> 209 <td> 210 <p><font size="2">Left ordinate of view</font></p> 211 </td> 212 </tr> 213 <tr> 214 <td> 215 <p align="center"><a name="y"></a><font size="2">y</font></p> 216 </td> 217 <td> 218 <p><font size="2">int</font></p> 219 </td> 220 <td> 221 <p><font size="2">void</font></p> 222 </td> 223 <td> 224 <p><font size="2">Top ordinate of view</font></p> 225 </td> 226 </tr> 227 <tr> 228 <td> 229 <p align="center"><a name="columns"></a><font size="2">columns</font></p> 230 </td> 231 <td> 232 <p><font size="2">size_t</font></p> 233 </td> 234 <td> 235 <p><font size="2">void</font></p> 236 </td> 237 <td> 238 <p><font size="2">Width of view</font></p> 239 </td> 240 </tr> 241 <tr> 242 <td> 243 <p align="center"><a name="rows"></a><font size="2">rows</font></p> 244 </td> 245 <td> 246 <p><font size="2">size_t</font></p> 247 </td> 248 <td> 249 <p><font size="2">void</font></p> 250 </td> 251 <td> 252 <p><font size="2">Height of view</font></p> 253 </td> 254 </tr> 255 </tbody> 256</table> 257</div> 258</body> 259</html> 260
