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 13 pixels. Image pixels (of type <a href="Quantum.html"><i>Quantum</i></a>) 14 may be accessed directly via the <i>Image Pixel Cache</i>. The image 15 pixel cache is a rectangular window (a view) into the actual image 16 pixels (which may be in memory, memory-mapped from a disk file, or 17 entirely on disk). Obtain existing image pixels via <i>get()</i>. 18 Create a new pixel region using <i>set().</i> </p> 19 <p>Depending on the capabilities of the operating system, and the 20 relationship of the window to the image, the pixel cache may be a copy 21 of the pixels in the selected window, or it may be the actual image 22 pixels. In any case calling <i>sync()</i> insures that the base image 23 is updated with the contents of the modified pixel cache. The method <i>decode()</i>supports 24 copying foreign pixel data formats into the pixel cache according to 25 the <i>QuantumTypes</i>. The method <i>encode()</i> supports copying 26 the pixels in the cache to a foreign pixel representation according to 27 the format specified by <i>QuantumTypes</i>. </p> 28 <p>Setting a view using the Pixels class does not cause the number of 29 references to the underlying image to be reduced to one. Therefore, in 30 order to ensure that only the current generation of the image is 31 modified, the Image's <a href="https://imagemagick.org/Magick++/Image++.html#modifyImage">modifyImage()</a> 32 method should be invoked to reduce the reference count on the underlying 33 image to one. If this is not done, then it is possible for a previous 34 generation of the image to be modified due to the use of reference 35 counting when copying or constructing an Image. </p> 36 <p>The <i>Quantum</i>* returned by the <i>set</i> and <i>get</i> 37 methods, and the <i>void</i>* returned by the <i>indexes</i> 38 method point to pixel data managed by the <i>Pixels</i> class. The <i>Pixels</i> 39 class is responsible for releasing resources associated with the pixel 40 view. This means that the pointer should never be passed to delete() or 41 free(). </p> 42 <p style="margin-bottom: 0cm;">The pixel view is a small image in which 43 the pixels may be accessed, addressed, and updated, as shown in the 44 following example, which produces an image similar to the one on the 45 right (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 #include <Magick++.h> 49 #include <iostream> 50 51 using namespace std; 52 using namespace Magick; 53 int main(int argc,char **argv) 54 { 55 InitializeMagick(*argv); 56 57 // Create base image 58 Image image(Geometry(254,218), "white"); 59 60 61 // Set the image type to TrueColor DirectClass representation. 62 image.type(TrueColorType); 63 // Ensure that there is only one reference to underlying image 64 // If this is not done, then image pixels will not be modified. 65 image.modifyImage(); 66 67 // Allocate pixel view 68 Pixels view(image); 69 70 // Set all pixels in region anchored at 38x36, with size 160x230 to green. 71 size_t columns = 196; size_t rows = 162; 72 Color green("green"); 73 Quantum *pixels = view.get(38,36,columns,rows); 74 for ( ssize_t row = 0; row < rows ; ++row ) 75 for ( ssize_t column = 0; column < columns ; ++column ) 76 { 77 *pixels++=QuantumRange*green.quantumRed(); 78 *pixels++=QuantumRange*green.quantumGreen(); 79 *pixels++=QuantumRange*green.quantumBlue(); 80 } 81 82 // Save changes to image. 83 view.sync(); 84 85 // Set all pixels in region anchored at 86x72, with size 108x67 to yellow. 86 columns = 108; rows = 67; 87 Color yellow("yellow"); 88 pixels = view.get(86,72,columns,rows); 89 for ( ssize_t row = 0; row < rows ; ++row ) 90 for ( ssize_t column = 0; column < columns ; ++column ) 91 { 92 *pixels++=QuantumRange*yellow.quantumRed(); 93 *pixels++=QuantumRange*yellow.quantumGreen(); 94 *pixels++=QuantumRange*yellow.quantumBlue(); 95 } 96 view.sync(); 97 98 // Set pixel at position 108,94 to red 99 Color red("red"); 100 pixels = view.get(108,94,1,1); 101 *pixels++=QuantumRange*red.quantumRed(); 102 *pixels++=QuantumRange*red.quantumGreen(); 103 *pixels++=QuantumRange*red.quantumBlue(); 104 105 // Save changes to image. 106 view.sync(); 107 image.write( "logo.png" ); 108 } 109 </div> 110 <p style="margin-bottom: 0cm;"><i>Pixels</i> supports the following 111 methods: </p> 112 <p align="center" style="margin-bottom: 0cm;"><b>Pixel Cache Methods</b></p> 113 <table width="100%" border="1" cellpadding="2" cellspacing="2"> 114 <tbody> 115 <tr> 116 <td> 117 <p align="center"><b>Method</b></p> 118 </td> 119 <td> 120 <p align="center"><b>Returns</b></p> 121 </td> 122 <td> 123 <p align="center"><b>Signature</b></p> 124 </td> 125 <td> 126 <p align="center"><b>Description</b></p> 127 </td> 128 </tr> 129 <tr> 130 <td> 131 <p align="center"><a name="get"></a><font size="2">get</font></p> 132 </td> 133 <td> 134 <p><font size="2"><a href="Quantum.html">Quantum</a>*</font></p> 135 </td> 136 <td> 137 <p><font size="2">const ssize_t x_, const ssize_t y_, const size_t 138 columns_, const size_t rows_</font></p> 139 </td> 140 <td> 141 <p><font size="2">Transfers read-write pixels from the image to 142 the pixel cache as defined by the specified rectangular region. 143 Modified pixels may be subsequently transferred back to the image 144 via <i>sync</i>. The value returned is intended for pixel access 145 only. It should never be deallocated.</font></p> 146 </td> 147 </tr> 148 <tr> 149 <td> 150 <p align="center"><a name="getConst"></a><font size="2">getConst</font></p> 151 </td> 152 <td> 153 <p><font size="2">const <a href="Quantum.html">Quantum</a>*</font></p> 154 </td> 155 <td> 156 <p><font size="2">const ssize_t x_, const ssize_t y_, const size_t 157 columns_, const size_t rows_</font></p> 158 </td> 159 <td> 160 <p><font size="2">Transfers read-only pixels from the image to 161 the pixel cache as defined by the specified rectangular region.</font></p> 162 </td> 163 </tr> 164 <tr> 165 <td> 166 <p align="center"><a name="set"></a><font size="2">set</font></p> 167 </td> 168 <td> 169 <p><font size="2"><a href="Quantum.html">Quantum</a>*</font></p> 170 </td> 171 <td> 172 <p><font size="2">const ssize_t x_, const ssize_t y_, const size_t 173 columns_, const size_t rows_</font></p> 174 </td> 175 <td> 176 <p><font size="2">Allocates a pixel cache region to store image 177 pixels as defined by the region rectangle. This area is 178 subsequently transferred from the pixel cache to the image via <i>sync</i>. 179 The value returned is intended for pixel access only. It should 180 never be deallocated.</font></p> 181 </td> 182 </tr> 183 <tr> 184 <td> 185 <p align="center"><a name="sync"></a><font size="2">sync</font></p> 186 </td> 187 <td> 188 <p><font size="2">void</font></p> 189 </td> 190 <td> 191 <p><font size="2">void</font></p> 192 </td> 193 <td> 194 <p><font size="2">Transfers the image cache pixels to the image.</font></p> 195 </td> 196 </tr> 197 <tr> 198 <td> 199 <p align="center"><a name="indexes"></a><font size="2">indexes</font></p> 200 </td> 201 <td> 202 <p><font size="2">void*</font></p> 203 </td> 204 <td> 205 <p><font size="2">void</font></p> 206 </td> 207 <td> 208 <p><font size="2">Returns the PsuedoColor pixel indexes 209 corresponding to the pixel region defined by the last <a href="Pixels.html#get">get</a> 210 , <a href="Pixels.html#getConst">getConst</a>, or <a href="Pixels.html#set">set</a> 211 call. Only valid for PseudoColor and CMYKA images. The pixel 212 indexes (an array of type <i>void</i>, which is typedef <i>Quantum</i>, 213 which is itself typedef <i>unsigned char</i>, or <i>unsigned short</i>, 214 depending on the value of the <i>QuantumDepth </i>define) provide 215 the <span lang="en-US">colormap</span> index (see <a 216 href="https://imagemagick.org/Magick++/Image++.html#colorMap">colorMap</a>) for each pixel in the 217 image. For CMYKA images, the indexes represent the black 218 channel. The value returned is intended for pixel access only. It 219 should never be deallocated.</font></p> 220 </td> 221 </tr> 222 <tr> 223 <td> 224 <p align="center"><a name="x"></a><font size="2">x</font></p> 225 </td> 226 <td> 227 <p><font size="2">int</font></p> 228 </td> 229 <td> 230 <p><font size="2">void</font></p> 231 </td> 232 <td> 233 <p><font size="2">Left ordinate of view</font></p> 234 </td> 235 </tr> 236 <tr> 237 <td> 238 <p align="center"><a name="y"></a><font size="2">y</font></p> 239 </td> 240 <td> 241 <p><font size="2">int</font></p> 242 </td> 243 <td> 244 <p><font size="2">void</font></p> 245 </td> 246 <td> 247 <p><font size="2">Top ordinate of view</font></p> 248 </td> 249 </tr> 250 <tr> 251 <td> 252 <p align="center"><a name="columns"></a><font size="2">columns</font></p> 253 </td> 254 <td> 255 <p><font size="2">size_t</font></p> 256 </td> 257 <td> 258 <p><font size="2">void</font></p> 259 </td> 260 <td> 261 <p><font size="2">Width of view</font></p> 262 </td> 263 </tr> 264 <tr> 265 <td> 266 <p align="center"><a name="rows"></a><font size="2">rows</font></p> 267 </td> 268 <td> 269 <p><font size="2">size_t</font></p> 270 </td> 271 <td> 272 <p><font size="2">void</font></p> 273 </td> 274 <td> 275 <p><font size="2">Height of view</font></p> 276 </td> 277 </tr> 278 </tbody> 279 </table> 280 </div> 281 </body> 282 </html> 283
