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6 <title>Magick::Pixels Class</title>
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10 <meta name="AUTHOR" content="Bob Friesenhahn">
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12 <meta name="CREATED" content="20020805;15302080">
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14 <meta name="CHANGEDBY" content="Bob Friesenhahn">
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16 <meta name="CHANGED" content="20020805;15341200">
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18 <meta name="DESCRIPTION" content="Class to access raw image pixels.">
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20 <meta name="KEYWORDS" content="ImageMagick,Pixel,Magick++">
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34<h1 align="center">Magick::Pixels</h1>
35<p>The <i>Pixels</i> class provides efficient access to raw image
36pixels. Image pixels (of type <a href="PixelPacket.html"><i>PixelPacket</i></a>)
37may be accessed directly via the <i>Image Pixel Cache</i>. The image
38pixel cache is a rectangular window (a view) into the actual image
39pixels (which may be in memory, memory-mapped from a disk file, or
40entirely on disk). Obtain existing image pixels via <i>get()</i>.
41Create a new pixel region using <i>set().</i> </p>
42<p>Depending on the capabilities of the operating system, and the
43relationship of the window to the image, the pixel cache may be a copy
44of the pixels in the selected window, or it may be the actual image
45pixels. In any case calling <i>sync()</i> insures that the base image
46is updated with the contents of the modified pixel cache. The method <i>decode()</i>supports
47copying foreign pixel data formats into the pixel cache according to
48the <i>QuantumTypes</i>. The method <i>encode()</i> supports copying
49the pixels in the cache to a foreign pixel representation according to
50the format specified by <i>QuantumTypes</i>. </p>
51<p>Setting a view using the Pixels class does not cause the number of
52references to the underlying image to be reduced to one. Therefore, in
53order to ensure that only the current generation of the image is
54modified, the Image's <a href="Image.html#modifyImage">modifyImage()</a>
55method should be invoked to reduce the reference count on the underlying
56image to one. If this is not done, then it is possible for a previous
57generation of the image to be modified due to the use of reference
58counting when copying or constructing an Image. </p>
59<p>The <i>PixelPacket</i>* returned by the <i>set</i> and <i>get</i>
60methods, and the <i>IndexPacket</i>* returned by the <i>indexes</i>
61method point to pixel data managed by the <i>Pixels</i> class. The <i>Pixels</i>
62class is responsible for releasing resources associated with the pixel
63view. This means that the pointer should never be passed to delete() or
64free(). </p>
65<p style="margin-bottom: 0cm;">The pixel view is a small image in which
66the pixels may be accessed, addressed, and updated, as shown in the
67following example, which produces an image similar to the one on the
68right (minus lines and text): <br>
69<br>
70</p>
71<table width="100%" border="0" cellpadding="2" cellspacing="2">
72 <tbody>
73 <tr>
74 <td>
75 <p><font size="2"><font face="Courier New, Courier"><font
76 color="#000099">   </font><font color="#ff0000">// Create base image</font></font></font>
77 <br>
78 <font size="2"><font face="Courier New, Courier"><font
79 color="#000099">   Image image(Geometry(254,218), "white");</font></font></font>
80 </p>
81
82 <p><font size="2"></font></p>
83 <p>   <font face="Courier New,Courier"><font color="#ff0000"><font
84 size="-1">  // Set the image type to TrueColor DirectClass
85representation.</font></font></font><br>
86 <font size="-1"><span
87 style="color: rgb(0, 0, 153); font-family: courier new,courier,monospace;"> 
88 image.type(TrueColorType</span></font><font size="-1"><span
89 style="color: rgb(0, 0, 153); font-family: courier new,courier,monospace;">);</span></font><br>
90 </p>
91
92 <p><font size="2"><font face="Courier New, Courier">   <font
93 color="#ff0000">// Ensure that there is only one reference to
94underlying image</font></font></font> <br>
95 <font size="2"><font face="Courier New, Courier"><font
96 color="#ff0000">   // If this is not done, then image pixels will
97not be modified.</font></font></font><br>
98 <font size="2"><font face="Courier New, Courier">   <font
99 color="#000099">image.modifyImage();<br>
100 </font></font></font></p>
101 <p><font size="2"><font face="Courier New, Courier"><font
102 color="#000099">  </font><font color="#ff0000"> // Allocate pixel
103view</font></font></font> <br>
104 <font size="2"><font face="Courier New, Courier"><font
105 color="#000099">   Pixels view(image);</font></font></font> </p>
106
107 <p><font size="2"><font face="Courier New, Courier"><font
108 color="#000099">  </font><font color="#ff0000"> // Set all pixels
109in region anchored at 38x36, with size 160x230 to green.</font></font></font> <br>
110 <font size="2"><font face="Courier New, Courier"><font
111 color="#000099">   unsigned int columns = 196; unsigned int rows =
112162;</font></font></font> <br>
113 <font size="2"><font face="Courier New, Courier"><font
114 color="#000099">   Color green("green");</font></font></font> <br>
115 <font size="2"><font face="Courier New, Courier"><font
116 color="#000099">   PixelPacket *pixels =
117view.get(38,36,columns,rows);</font></font></font> <br>
118 <font size="2"><font face="Courier New, Courier"><font
119 color="#000099">   for ( int row = 0; row &lt; rows ; ++row )</font></font></font>
120 <br>
121 <font size="2"><font face="Courier New, Courier"><font
122 color="#000099">     for ( int column = 0; column &lt; columns ;
123++column )</font></font></font> <br>
124 <font size="2"><font face="Courier New, Courier"><font
125 color="#000099">       *pixels++=green;</font></font></font> </p>
126 <p><font size="2"><font face="Courier New, Courier"><font
127 color="#000099">  </font><font color="#ff0000"> // Save changes to
128image.<br>
129 </font></font></font><font size="2"></font><font size="2"><font
130 face="Courier New, Courier"><font color="#000099">   view.sync();</font></font></font>
131 </p>
132
133 <p><font size="2"><font face="Courier New, Courier"><font
134 color="#000099">  </font><font color="#ff0000"> // Set all pixels
135in region anchored at 86x72, with size 108x67 to yellow.</font></font></font> <br>
136 <font size="2"><font face="Courier New, Courier"><font
137 color="#000099">   columns = 108; rows = 67;</font></font></font> <br>
138 <font size="2"><font face="Courier New, Courier"><font
139 color="#000099">   Color yellow("yellow");</font></font></font> <br>
140 <font size="2"><font face="Courier New, Courier"><font
141 color="#000099">   pixels = view.get(86,72,columns,rows);</font></font></font> <br>
142 <font size="2"><font face="Courier New, Courier"><font
143 color="#000099">   for ( int row = 0; row &lt; rows ; ++row )</font></font></font>
144 <br>
145 <font size="2"><font face="Courier New, Courier"><font
146 color="#000099">      for ( int column = 0; column &lt; columns ;
147++column )</font></font></font> <br>
148 <font size="2"><font face="Courier New, Courier"><font
149 color="#000099">         *pixels++=yellow;</font></font></font> <br>
150 <font size="2"><font face="Courier New, Courier"><font
151 color="#000099">    view.sync();</font></font></font> </p>
152
153 <p><font size="2"><font face="Courier New, Courier"><font
154 color="#000099">  </font><font color="#ff0000"> // Set pixel at
155position 108,94 to red</font></font></font> <br>
156 <font size="2"><font face="Courier New, Courier"><font
157 color="#000099">   *(view.get(108,94,1,1)) = Color("red");</font></font></font> </p>
158 <p><font size="2"><font face="Courier New, Courier"><font
159 color="#000099">  </font><font color="#ff0000"> // Save changes to
160image.<br>
161 </font></font></font><font size="2"><font
162 face="Courier New, Courier"><font color="#000099">   view.sync();<br>
163 <br>
164 </font></font></font></p>
165 </td>
166 <td>
167 <p><img src="Cache.png" name="Graphic1" align="bottom" width="254"
168 height="218" border="0"></p>
169 </td>
170 </tr>
171 </tbody>
172</table>
173<p style="margin-bottom: 0cm;"><i>Pixels</i> supports the following
174methods: <br>
175<br>
176</p>
177<p align="center" style="margin-bottom: 0cm;"><b>Pixel Cache Methods</b></p>
178<table width="100%" border="1" cellpadding="2" cellspacing="2">
179 <tbody>
180 <tr>
181 <td>
182 <p align="center"><b>Method</b></p>
183 </td>
184 <td>
185 <p align="center"><b>Returns</b></p>
186 </td>
187 <td>
188 <p align="center"><b>Signature</b></p>
189 </td>
190 <td>
191 <p align="center"><b>Description</b></p>
192 </td>
193 </tr>
194 <tr>
195 <td>
196 <p align="center"><a name="get"></a><font size="2">get</font></p>
197 </td>
198 <td>
199 <p><font size="2"><a href="PixelPacket.html">PixelPacket</a>*</font></p>
200 </td>
201 <td>
202 <p><font size="2">const int x_, const int y_, const unsigned
203const int columns_, const unsigned int rows_</font></p>
204 </td>
205 <td>
206 <p><font size="2">Transfers read-write pixels from the image to
207the pixel cache as defined by the specified rectangular region.
208 Modified pixels may be subsequently transferred back to the image
209 via <i>sync</i>. The value returned is intended for pixel access
210 only. It should never be deallocated.</font></p>
211 </td>
212 </tr>
213 <tr>
214 <td>
215 <p align="center"><a name="getConst"></a><font size="2">getConst</font></p>
216 </td>
217 <td>
218 <p><font size="2">const <a href="PixelPacket.html">PixelPacket</a>*</font></p>
219 </td>
220 <td>
221 <p><font size="2">const int x_, const int y_, const unsigned int
222 columns_, const unsigned int rows_</font></p>
223 </td>
224 <td>
225 <p><font size="2">Transfers read-only pixels from the image to
226the pixel cache as defined by the specified rectangular region.</font></p>
227 </td>
228 </tr>
229 <tr>
230 <td>
231 <p align="center"><a name="set"></a><font size="2">set</font></p>
232 </td>
233 <td>
234 <p><font size="2"><a href="PixelPacket.html">PixelPacket</a>*</font></p>
235 </td>
236 <td>
237 <p><font size="2">const int x_, const int y_, const unsigned int
238 columns_, const unsigned int rows_</font></p>
239 </td>
240 <td>
241 <p><font size="2">Allocates a pixel cache region to store image
242 pixels as defined by the region rectangle.  This area is
243 subsequently transferred from the pixel cache to the image via <i>sync</i>.
244The value returned is intended for pixel access only. It should
245never be deallocated.</font></p>
246 </td>
247 </tr>
248 <tr>
249 <td>
250 <p align="center"><a name="sync"></a><font size="2">sync</font></p>
251 </td>
252 <td>
253 <p><font size="2">void</font></p>
254 </td>
255 <td>
256 <p><font size="2">void</font></p>
257 </td>
258 <td>
259 <p><font size="2">Transfers the image cache pixels to the image.</font></p>
260 </td>
261 </tr>
262 <tr>
263 <td>
264 <p align="center"><a name="indexes"></a><font size="2">indexes</font></p>
265 </td>
266 <td>
267 <p><font size="2">IndexPacket*</font></p>
268 </td>
269 <td>
270 <p><font size="2">void</font></p>
271 </td>
272 <td>
273 <p><font size="2">Returns the PsuedoColor pixel indexes
274 corresponding to the pixel region defined by the last <a href="#get">get</a>
275 , <a href="#getConst">getConst</a>, or <a href="#set">set</a>
276 call. Only valid for PseudoColor and CMYKA images. The pixel
277 indexes (an array of type <i>IndexPacket</i>, which is typedef <i>Quantum</i>,
278which is itself typedef <i>unsigned char</i>, or <i>unsigned short</i>,
279depending on the value of the <i>QuantumDepth </i>define) provide
280the <span lang="en-US">colormap</span> index (see <a
281 href="Image.html#colorMap">colorMap</a>) for each pixel in the
282image. For CMYKA images, the indexes represent the black
283channel. The value returned is intended for pixel access only. It
284should never be deallocated.</font></p>
285 </td>
286 </tr>
287 <tr>
288 <td>
289 <p align="center"><a name="x"></a><font size="2">x</font></p>
290 </td>
291 <td>
292 <p><font size="2">int</font></p>
293 </td>
294 <td>
295 <p><font size="2">void</font></p>
296 </td>
297 <td>
298 <p><font size="2">Left ordinate of view</font></p>
299 </td>
300 </tr>
301 <tr>
302 <td>
303 <p align="center"><a name="y"></a><font size="2">y</font></p>
304 </td>
305 <td>
306 <p><font size="2">int</font></p>
307 </td>
308 <td>
309 <p><font size="2">void</font></p>
310 </td>
311 <td>
312 <p><font size="2">Top ordinate of view</font></p>
313 </td>
314 </tr>
315 <tr>
316 <td>
317 <p align="center"><a name="columns"></a><font size="2">columns</font></p>
318 </td>
319 <td>
320 <p><font size="2">unsigned int</font></p>
321 </td>
322 <td>
323 <p><font size="2">void</font></p>
324 </td>
325 <td>
326 <p><font size="2">Width of view</font></p>
327 </td>
328 </tr>
329 <tr>
330 <td>
331 <p align="center"><a name="rows"></a><font size="2">rows</font></p>
332 </td>
333 <td>
334 <p><font size="2">unsigned int</font></p>
335 </td>
336 <td>
337 <p><font size="2">void</font></p>
338 </td>
339 <td>
340 <p><font size="2">Height of view</font></p>
341 </td>
342 </tr>
343 </tbody>
344</table>
345<p><br>
346<br>
347</p>
348</body>
349</html>