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149
150<p class="navigation-index">[<a href="#overview">Architecture Overview</a> &bull; <a href="#cache">The Pixel Cache</a> &bull; <a href="#stream">Streaming Pixels</a> &bull; <a href="#properties">Image Properties and Profiles</a> &bull; <a href="#threads">Threads of Execution</a> &bull; <a href="#coders">Custom Image Coders</a> &bull; <a href="#filters">Custom Image Filters</a>]</p>
151
152<div class="doc-section">
153<p>The citizens of Oz were quite content with their benefactor, the all-powerful Wizard. They accepted his wisdom and benevolence without ever questioning the who, why, and where of his power. Like the citizens of Oz, if you feel comfortable that ImageMagick can help you convert, edit, or compose your images without knowing what goes on behind the curtain, feel free to skip this section. However, if you want to know more about the software and algorithms behind ImageMagick, read on. To fully benefit from this discussion, you should be comfortable with image nomenclature and be familiar with computer programming.</p>
154</div>
155
156<h2><a name="overview"></a>Architecture Overview</h2>
157<div class="doc-section">
158
159<p>An image typically consists of a rectangular region of pixels and metadata. To convert, edit, or compose an image in an efficient manner we need convenient access to any pixel anywhere within the region (and sometimes outside the region). And in the case of an image sequence, we need access to any pixel of any region of any image in the sequence. However, there are hundreds of image formats such JPEG, TIFF, PNG, GIF, etc., that makes it difficult to access pixels on demand. Within these formats we find differences in:</p>
160
161<ul>
162 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
163 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
164 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
165 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
166 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
167 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
168</ul>
169
170<p>In addition, some image pixels may require attenuation, some formats permit more than one frame, and some formats contain vector graphics that must first be rasterized (converted from vector to pixels).</p>
171
172<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
173
174<ul>
175 <li>one pixel a time (e.g. pixel at location 10,3)</li>
176 <li>a single scanline (e.g. all pixels from row 4)</li>
177 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
178 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
179 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
180 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
181 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
182 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
183 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
184 <li>a high-dynamic range pixel that can include negative values as well as values that exceed the quantum depth (e.g. -0.00716)</li>
185 <li>one or more pixels simultaneously in different threads of execution</li>
186</ul>
187
188<p>In addition, some images include a clip mask that define which pixels are eligible to be updated. Pixels outside the area defined by the clip mask remain untouched.</p>
189
190<p>Given the varied image formats and image processing requirements, we implemented the ImageMagick <a href="#cache">pixel cache</a> to provide convenient sequential or parallel access to any pixel on demand anywhere inside the image region and from any image in a sequence. In addition, the pixel cache permits access to pixels outside the boundaries defined by the image (we call these <a href="#virtual-pixels">virtual pixels</a>).</p>
191
192<p>In addition to pixels, images have a plethora of <a href="#properties">image properties and profiles</a>. Properties include the well known items such as width, height, depth, and colorspace. An image may have optional properties which might include the image author, a comment, a create date, and others. Some images also include profiles for color management, or EXIF, IPTC, 8BIM, or XMP informational profiles. ImageMagick provides command line options and programming methods to get, set, or view image properties or profiles or apply profiles.</p>
193
194<p>ImageMagick consists of more than 375,000 lines of C code and optionally depends on several million lines of code in dependent libraries (e.g. JPEG, PNG, TIFF libraries). Given that, one might expect a huge architecture document. However, a great majority of image processing is simply accessing pixels and its metadata and our simple and elegant implementation makes this easy for the ImageMagick developer. We discuss the implementation of the pixel cache and getting and setting image properties and profiles in the next few sections. Next, we discuss using ImageMagick within a <a href="#threads">thread</a> of execution. In the final sections, we discuss <a href="#coders">image coders</a> to read or write a particular image format followed by a few words on creating a <a href="#filters">filter</a> to access or update pixels based on your custom requirements.</p>
195
196</div>
197
198<h2><a name="cache"></a>The Pixel Cache</h2>
199<div class="doc-section">
200
201<p>The ImageMagick pixel cache is a repository for image pixels with up to 5 channels. The first 4 channels are stored contiguously and an optional second area follows with 1 channel. The channels are at the depth specified when ImageMagick was built. The channel depths are 8 bits-per-pixel component for the Q8 version of ImageMagick, 16 bits-per-pixel component for the Q16 version, and 32 bits-per-pixel component for the Q32 version. By default pixel components are unsigned quantities, however, if you use the <a href="../www/high-dynamic-range.html">high dynamic-range</a> version of ImageMagick, the components are 32-bit floating point. The primary 4 channels can hold any value but typically contain red, green, blue, and alpha intensities or cyan, magenta, yellow, and alpha intensities. The optional fifth channel contains the colormap indexes for colormapped images or the black channel for CMYK images. The pixel cache storage may be heap memory, anonymous memory mapped memory, disk-backed memory mapped, or on disk. The pixel cache is reference-counted. Only the cache properties are copied when the cache is cloned. The cache pixels are subsequently copied when you signal your intention to update any of the pixels.</p>
202
203<h3>Create the Pixel Cache</h3>
204<div class="doc-section">
205
206<p>The pixel cache is associated with an image when it is created and it is initialized when you try to get or put pixels. Here are three common methods to associate a pixel cache with an image:</p>
207
208<h4>Create an image canvas initialized to the background color:</h4>
209<p class="code">
210 image=AllocateImage(image_info);
211 if (SetImageExtent(image,640,480) == MagickFalse)
212 { /* an exception was thrown */ }
213 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
214 SetImageBackgroundColor(image);
215</p>
216
217<h4>Create an image from a JPEG image on disk:</h4>
218<p class="code"> (void) strcpy(image_info-&gt;filename,"image.jpg"):
219 image=ReadImage(image_info,exception);
220 if (image == (Image *) NULL)
221 { /* an exception was thrown */ }
222</p>
223<h4>Create an image from a memory based image:</h4>
224<p class="code">
225 image=BlobToImage(blob_info,blob,extent,exception);
226 if (image == (Image *) NULL)
227 { /* an exception was thrown */ }
228</p>
229
230<p>In our discussion of the pixel cache we use the <a href="../www/magick-core.html">MagickCore API</a> to illustrate our points, however, the principles are the same for other program interfaces to ImageMagick.</p>
231
232<p>When the pixel cache is initialized, pixels are scaled from whatever bit depth they originated from to that required by the pixel cache. For example, a 1-channel 1-bit monochrome PBM image is scaled to a 4 channel 8-bit RGBA image, if you are using the Q8 version of ImageMagick, and 16-bit RGBA for the Q16 version. You can determine which version you have using the <a href="../www/command-line-options.html#version">&#x2011;version</a> option, as with this command: </p>
233
234<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.5.5-6 2009-09-01 Q16 http://www.imagemagick.org</span></p>
235<p>As you can see, the convenience of the pixel cache sometimes comes with a trade-off in storage (e.g. storing a 1-bit monochrome image as 16-bit RGBA is wasteful) and speed (i.e. storing the entire image in memory is generally slower than accessing one scanline of pixels at a time).</p>
236</div>
237
238<h3>Access the Pixel Cache</h3>
239<div class="doc-section">
240
241<p>Once the pixel cache is associated with an image, you typically want to get, update, or put pixels into it. We refer to pixels inside the image region as <em>authentic pixels</em> and outside the region as <em>virtual pixels</em>. Use these methods to access the pixels in the cache:</p>
242<ul>
243 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify</li>
244 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
245 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
246 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
247</ul>
248
249<p>Here is a typical <a href="../www/magick-core.html">MagickCore</a> code snippet for manipulating pixels in the pixel cache. In our example we copy pixels from the input image to the output image and decrease the intensity by 10%:</p>
250
251<div class="viewport">
252<pre class="code">
253 long
254 x,
255 y;
256
257 const PixelPacket
258 *p;
259
260 PixelPacket
261 *q;
262
263 destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
264 if (destination == (Image *) NULL)
265 { /* an exception was thrown */ }
266 for (y=0; y &lt; (long) source-&gt;rows; y++)
267 {
268 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
269 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
270 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
271 break;
272 for (x=0; x &lt; (long) source-&gt;columns; x++)
273 {
274 q-&gt;red=90*p-&gt;red/100;
275 q-&gt;green=90*p-&gt;green/100;
276 q-&gt;blue=90*p-&gt;blue/100;
277 q-&gt;opacity=90*p-&gt;opacity/100;
278 p++;
279 q++;
280 }
281 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
282 break;
283 }
284 if (y &lt; (long) source-&gt;rows)
285 { /* an exception was thrown */ }
286</pre>
287</div>
288
289<p>When we first create the destination image by cloning the source image, the pixel cache pixels are not copied. They are only copied when you signal your intentions to modify the pixel cache by calling <a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> or <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a>. Use <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> if you want to set new pixel values rather than update existing ones. Finally, use <a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p>
290
291<p>Recall how we mentioned that the indexes of a colormapped image or the black channel of a CMYK image are stored separately. Use <a href="../www/api/cache.html#GetVirtualIndexes">GetVirtualIndexes()</a> (to read the indexes) or <a href="../www/api/cache.html#GetAuthenticIndexes">GetAuthenticIndexes()</a> (to update the indexes) to gain access to this channel. For example, to print the colormap indexes, use:</p>
292
293<pre class="code">
294 const IndexPacket
295 *indexes;
296
297 for (y=0; y &lt; (long) source-&gt;rows; y++)
298 {
299 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
300 if (p == (const PixelPacket *) NULL)
301 break;
302 indexes=GetVirtualIndexes(source);
303 for (x=0; x &lt; (long) source-&gt;columns; x++)
304 (void) printf("%d\n",indexes[x];
305 }
306 if (y &lt; (long) source-&gt;rows)
307 /* an exception was thrown */
308</pre>
309
310<p>The pixel cache manager decides whether to give you direct or indirect access to the image pixels. In some cases the pixels are staged to an intermediate buffer-- and that is why you must call SyncAuthenticPixels() to ensure this buffer is <em>pushed</em> out to the pixel cache to guarantee the corresponding pixels in the cache are updated. For this reason we recommend that you only read or update a scanline or a few scanlines of pixels at a time. However, you can get any rectangular region of pixels you want. GetAuthenticPixels() requires that the region you request is within the bounds of the image area. For a 640 by 480 image, you can get a scanline of 640 pixels but if you ask for 641 pixels, an exception is returned. GetVirtualPixels() does not have this constraint. For example,</p>
311
312<pre class="code">
313 p=GetVirtualPixels(source,-3,3,source-&gt;columns+7,7,exception);
314</pre>
315
316<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
317</div>
318
319<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
320<div class="doc-section">
321
322 <p>Access to the virtual pixels are controlled by the <a href="../www/api/cache.html#SetImageVirtualPixelMethod">SetImageVirtualPixelMethod()</a> method from the MagickCore API or the <a href="../www/command-line-options.html#virtual-pixel">&#x2011;virtual&#x2011;pixel</a> option from the command line. The methods include:</p>
323
324<pre class="text">
325 background: the area surrounding the image is the background color
326 black: the area surrounding the image is black
327 checker-tile: alternate squares with image and background color
328 dither: non-random 32x32 dithered pattern
329 edge: extend the edge pixel toward infinity
330 gray: the area surrounding the image is gray
331 horizontal-tile: horizontally tile the image, background color above/below
332 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
333 mirror: mirror tile the image
334 random: choose a random pixel from the image
335 tile: tile the image (default)
336 transparent: the area surrounding the image is transparent blackness
337 vertical-tile: vertically tile the image, sides are background color
338 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
339 white: the area surrounding the image is white
340</pre>
341
342<p>There is a plethora of image processing algorithms that require a neighborhood of pixels about a pixel of interest. There is typically a caveat concerning how to handle pixels around the image boundaries, known as edge pixels. With virtual pixels, you do not need to concern yourself about special edge processing other than choosing which virtual pixel method is most appropriate for your algorithm.</p>
343</div>
344
345<h3>Cache Storage and Resource Requirements</h3>
346<div class="doc-section">
347
348<p>We mentioned previously that this simple and elegant design of the ImageMagick pixel cache comes at a cost in terms of storage and processing speed. The pixel cache storage requirements scales with the area of the image and the bit depth of the pixel components. For example, if we have a 640 by 480 image and we're using the Q16 version of ImageMagick, the pixel cache consumes image <em>width * height * bit-depth / 8 * channels</em> bytes or approximately 2.3 megabytes (i.e. 640 * 480 * 2 * 4). Not too bad, but what if your image is 25000 by 25000 pixels? The pixel cache requires approximately 4.7 gigabytes of storage. Ouch. ImageMagick accounts for possible huge storage requirements by caching large images to disk rather than memory. Typically the pixel cache is stored in memory using heap memory. If heap memory is exhausted, pixels are stored in in an anonymous map; if the anonymous memory map is exhausted, we create the pixel cache on disk and attempt to memory-map it; and if memory-map memory is exhausted, we simply use standard disk I/O. Disk storage is cheap but it is also very slow, upwards of 1000 times slower than memory. We can get some speed improvements, up to 5 times, if we use memory mapping to the disk-based cache. These decisions about storage are made <em>automagically</em> by the pixel cache manager negotiating with the operating system. However, you can influence how the pixel cache manager allocates the pixel cache with <em>cache resource limits</em>. The limits include:</p>
349
350<dl class="doc">
351 <dt class="doc">files</dt>
352 <dd>maximum number of open pixel cache files. When this limit is exceeded, any subsequent pixels cached to disk are closed and reopened on demand. This behavior permits a large number of images to be accessed simultaneously on disk, but with a speed penalty due to repeated open/close calls.</dd>
353 <dt class="doc">area</dt>
354 <dd>maximum area in bytes of any one image that can reside in the pixel cache memory. If this limit is exceeded, the image is automagically cached to disk.</dd>
355 <dt class="doc">memory</dt>
356 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
357 <dt class="doc">map</dt>
358 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
359 <dt class="doc">disk</dt>
360 <dd>maximum amount of disk space in bytes permitted for use by the pixel cache. If this limit is exceeded, the pixel cache is not created and a fatal exception is thrown.</dd>
361</dl>
362
363<p>To determine the current setting of these limits, use this command:</p>
364
365<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span><span class='crtout'><pre>File Area Memory Map Disk Thread Time
366-------------------------------------------------------------------
367 768 3.8187gb 2.864gb 7.6375gb 16eb 2 unlimited</pre></span></p>
368<p>You can set these limits either with <a href="../www/resources.html#environment">environment variables</a>, the <a href="../www/command-line-options.html#limit">-limit</a> command line option, or the <a href="../www/api/resource.html#SetMagickResourceLimit">SetMagickResourceLimit()</a> MagickCore API method. As an example, our online web interface to ImageMagick, <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">ImageMagick Studio</a>, has an area limit of 64 megabytes, a memory limit of 128 megabytes and a map limit of 256 megabytes and a disk limit of 1 gigabytes. Since we process multiple simultaneous sessions, we don't want any one session consuming all the available memory. Instead large images are cached to disk. If the image is too large and exceeds the pixel cache disk limit, the program exits. In addition, we place a 60 second time limit to prevent any run-away processing tasks.</p>
369
370<p>Note, the cache limits are global, meaning if you create several images, the combined resource requirements are compared to the limit to determine the pixel cache storage disposition.</p>
371</div>
372
373<h3>Cache Views</h3>
374<div class="doc-section">
375
376<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() from the MagickCore API can only deal with one pixel cache area per image at a time. Suppose you want to access the first and last scanline from the same image at the same time? The solution is to use a <em>cache view</em>. A cache view permits you to access as many areas simultaneously in the pixel cache as you require. The cache view <a href="../www/api/cache-view.html">methods</a> behave like the previous methods except you must first open a view and close it when you are finished with it. Here is a snippet of MagickCore code that permits us to access two areas of an image simultaneously:</p>
377
378<pre class="code">
379 CacheView
380 *view_1,
381 *view_2;
382
383 view_1=OpenCacheView(source);
384 view_2=OpenCacheView(source);
385 for (y=0; y &lt; (long) source-&gt;rows; y++)
386 {
387 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
388 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,exception);
389 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
390 break;
391 for (x=0; x &lt; (long) source-&gt;columns; x++)
392 {
393 /* do something with u &amp; v here */
394 }
395 }
396 view_1=CloseCacheView(view_1);
397 view_2=CloseCacheView(view_2);
398 if (y &lt; (long) source-&gt;rows)
399 { /* an exception was thrown */ }
400</pre>
401</div>
402
403<h3>Magick Persistent Cache Format</h3>
404<div class="doc-section">
405
406<p>Recall that each image format is decoded by ImageMagick and the pixels are deposited in the pixel cache. If you write an image, the pixels are read from the pixel cache and encoded as required by the format you are writing (e.g. GIF, PNG, etc.). The Magick Persistent Cache (MPC) format is designed to eliminate the overhead of decoding and encoding pixels to and from an image format. MPC writes two files. One, with the extension <kbd>.mpc</kbd>, retains all the properties associated with the image or image sequence (e.g. width, height, colorspace, etc.) and the second, with the extension <kbd>.cache</kbd>, is the pixel cache in the native format. When reading an MPC image file, ImageMagick reads the image properties and memory maps the pixel cache on disk eliminating the need for decoding the image pixels. The tradeoff is in disk space. MPC is generally larger in file size than most other image formats.</p>
407</div>
408
409<h3>Best Practices</h3>
410<div class="doc-section">
411
412<p>Although you can request any pixel from the pixel cache, any block of pixels, any scanline, multiple scanlines, any row, or multiple rows with the GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels, GetCacheViewVirtualPixels(), GetCacheViewAuthenticPixels(), and QueueCacheViewAuthenticPixels() methods, ImageMagick is optimized to return a few pixels or a few pixels rows at time. There are additional optimizations if you request a single scanline or a few scanlines at a time. These methods also permit random access to the pixel cache, however, ImageMagick is optimized for sequential access.</p>
413
414<p>If you update pixels returned from GetAuthenticPixels() or GetCacheViewAuthenticPixels(), don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to ensure your changes are synchronized with the pixel cache.</p>
415
416<p>Use QueueAuthenticPixels() or QueueCacheViewAuthenticPixels() if you are setting an initial pixel value. The GetAuthenticPixels() or GetCacheViewAuthenticPixels() method reads pixels from the cache and if you are setting an initial pixel value, this read is unnecessary. Don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to push your updates to the pixel cache.</p>
417
418<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() are slightly more efficient than their cache view counter-parts. However, cache views are required if you need access to more than one region of the image simultaneously or if more than one <a href="#threads">thread of execution</a> is accessing the image.</p>
419
420<p>You can request pixels outside the bounds of the image with GetVirtualPixels() or GetCacheViewVirtualPixels(), however, it is more efficient to request pixels within the confines of the image region.</p>
421
422<p>Although you can force the pixel cache to disk using appropriate resource limits, disk access can be upwards of 1000 times slower than memory access. For fast, efficient, access to the pixel cache, try to keep the pixel cache in heap memory or anonymous mapped memory.</p>
423
424<p>The ImageMagick Q16 version of ImageMagick permits you to read and write 16 bit images without scaling but the pixel cache consumes twice as much resources as the Q8 version. If your system has constrained memory or disk resources, consider the Q8 version of ImageMagick. In addition, the Q8 version typically executes faster than the Q16 version.</p>
425
426<p>A great majority of image formats and algorithms restrict themselves to a fixed range of pixel values from 0 to some maximum value, for example, the Q16 version of ImageMagick permit intensities from 0 to 65535. High dynamic-range imaging (HDRI), however, permits a far greater dynamic range of exposures (i.e. a large difference between light and dark areas) than standard digital imaging techniques. HDRI accurately represents the wide range of intensity levels found in real scenes ranging from the brightest direct sunlight to the deepest darkest shadows. Enable <a href="../www/high-dynamic-range.html">HDRI</a> at ImageMagick build time to deal with high dynamic-range images, but be mindful that each pixel component is a 32-bit floating point value. In addition pixel values are not clamped so some algorithms may perform differently than the non-HDRI version.</p>
427
428<p>If you are dealing with large images, make sure the pixel cache is written to a disk area with plenty of free space. Under Unix, this is typically <kbd>/tmp</kbd> and for Windows, <kbd>c:/temp</kbd>. You can tell ImageMagick to write the pixel cache to an alternate location with the MAGICK_TMPDIR environment variable. For example,</p>
429
430<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>export MAGICK_TMPDIR=/data/magick</span></p>
431
432<p>If you plan on processing the same image many times, consider the MPC format. Reading a MPC image has near-zero overhead because its in the native pixel cache format eliminating the need for decoding the image pixels. Here is an example:</p>
433
434<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.tif image.mpc</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+0+0 +repage 1.png</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+100+0 +repage 2.png</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+200+0 +repage 3.png</span></p>
435<p>MPC is ideal for web sites. It reduces the overhead of reading and writing an image. We use it exclusively at our <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">online image studio</a>.</p>
436</div>
437
438</div>
439
440<h2><a name="stream"></a>Streaming Pixels</h2>
441<div class="doc-section">
442
443<p>ImageMagick provides for streaming pixels as they are read from or written to an image. This has several advantages over the pixel cache. The time and resources consumed by the pixel cache scale with the area of an image, whereas the pixel stream resources scale with the width of an image. The disadvantage is the pixels must be consumed as they are streamed so there is no persistence.</p>
444
445<p>Use <a href="../www/api/stream.html#ReadStream">ReadStream()</a> or <a href="../www/api/stream.html#WriteStream">WriteStream()</a> with an appropriate callback method in your MagickCore program to consume the pixels as they are streaming. Here's an abbreviated example of using ReadStream:</p>
446
447<pre class="code">
448static size_t StreamHandler(const Image *image,const void *pixels,
449 const size_t columns)
450{
451 /* process pixels here */
452 return(columns);
453}
454
455...
456/* invoke the pixel stream here */
457image=ReadStream(image_info,&amp;StreamHandler,exception);
458</pre>
459
460<p>We also provide a lightweight tool, <a name="stream"></a><a href="../www/stream.html">stream</a>, to stream one or more pixel components of the image or portion of the image to your choice of storage formats. It writes the pixel components as they are read from the input image a row at a time making <a name="stream"></a><a href="../www/stream.html">stream</a> desirable when working with large images or when you require raw pixel components.</p>
461
462</div>
463
464<h2><a name="properties"></a>Image Properties and Profiles</h2>
465<div class="doc-section">
466
467<p>Images have metadata associated with them in the form of properties (e.g. width, height, description, etc.) and profiles (e.g. EXIF, IPTC, color management). ImageMagick provides convenient methods to get, set, or update image properties and get, set, update, or apply profiles. Some of the more popular image properties are associated with the Image structure in the MagickCore API. For example:</p>
468
469<pre class="code">
470 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
471</pre>
472
473<p>For a great majority of image properties, such as an image comment or description, we use the <a href="../www/api/property.html#GetImageProperty">GetImageProperty()</a> and <a href="../www/api/property.html#SetImageProperty">SetImageProperty()</a> methods. Here we set a property and fetch it right back:</p>
474
475<pre class="code">
476 const char
477 *comment;
478
479 (void) SetImageProperty(image,"comment","This space for rent");
480 comment=GetImageProperty(image,"comment");
481 if (comment == (const char *) NULL)
482 (void) printf("Image comment: %s\n",comment);
483</pre>
484
485<p>Image profiles are handled with <a href="../www/api/profile.html#GetImageProfile">GetImageProfile()</a>, <a href="../www/api/profile.html#SetImageProfile">SetImageProfile()</a>, and <a href="../www/api/profile.html#ProfileImage">ProfileImage()</a> methods. Here we set a profile and fetch it right back:</p>
486
487<pre class="code">
488 StringInfo
489 *profile;
490
491 profile=AcquireStringInfo(length);
492 SetStringInfoDatum(profile,my_exif_profile);
493 (void) SetImageProfile(image,"EXIF",profile);
494 DestroyStringInfo(profile);
495 profile=GetImageProfile(image,"EXIF");
496 if (profile != (StringInfo *) NULL)
497 (void) PrintStringInfo(stdout,"EXIF",profile);
498</pre>
499
500</div>
501
502<h2><a name="threads"></a>Threads of Execution</h2>
503<div class="doc-section">
504
505<p>Many of ImageMagick's internal algorithms are threaded to take advantage of speed-ups offered by the dual and quad-core processor technologies. However, you are welcome to use ImageMagick algorithms in your threads of execution with the exception of the MagickCore's GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), or SyncAuthenticPixels() pixel cache methods. These methods are intended for one thread of execution only. To access the pixel cache with more than one thread of execution, use a cache view. We do this for the <a href="../www/api/composite.html#CompositeImage">CompositeImage()</a> method, for example. Suppose we want to composite a single image over a different image in each thread of execution. If we use GetVirtualPixels(), the results are unpredictable because multiple threads would likely be asking for different areas of the pixel cache simultaneously. Instead we use GetCacheViewVirtualPixels() which creates a unique view for each thread of execution ensuring our program behaves properly regardless of how many threads are invoked. The other program interfaces, such as the <a href="../www/magick-wand.html">MagickWand API</a>, are completely thread safe so there are no special precautions for threads of execution.</p>
506
507<p>Here is an example of how ImageMagick can take advantage of threads of execution with the OpenMP programming paradigm:</p>
508
509<div class="viewport">
510<pre class="code">
511{
512 CacheView
513 *image_view;
514
515 long
516 y;
517
518 MagickBooleanType
519 status;
520
521 status=MagickTrue;
522 image_view=AcquireCacheView(image);
523 #pragma omp parallel for schedule(dynamic,4) shared(status)
524 for (y=0; y &lt; (long) image-&gt;rows; y++)
525 {
526 register IndexPacket
527 *indexes;
528
529 register long
530 x;
531
532 register PixelPacket
533 *q;
534
535 if (status == MagickFalse)
536 continue;
537 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
538 if (q == (PixelPacket *) NULL)
539 {
540 status=MagickFalse;
541 continue;
542 }
543 indexes=GetCacheViewAuthenticIndexQueue(image_view);
544 for (x=0; x &lt; (long) image-&gt;columns; x++)
545 {
546 q-&gt;red= ...
547 q-&gt;green= ...
548 q-&gt;blue= ...
549 q-&gt;opacity= ...
550 if (indexes != (IndexPacket *) NULL)
551 indexes[x]= ...
552 q++;
553 }
554 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
555 status=MagickFalse;
556 }
557 image_view=DestroyCacheView(image_view);
558 if (status == MagickFalse)
559 perror("something went wrong");
560}
561</pre>
562</div>
563
564<p>If you call the ImageMagick API from your OpenMP-enabled application and you intend to dynamically increase the number of threads available in subsequent parallel regions, be sure to perform the increase <em>before</em> you call the API otherwise ImageMagick may fault.</p>
565
566</div>
567
568<h2><a name="coders"></a>Custom Image Coders</h2>
569<div class="doc-section">
570
571<p>An image coder (i.e. encoder / decoder) is responsible for registering, optionally classifying, optionally reading, optionally writing, and unregistering one image format (e.g. PNG, GIF, JPEG, etc.). Registering an image coder alerts ImageMagick a particular format is available to read or write. While unregistering tells ImageMagick the format is no longer available. The classifying method looks at the first few bytes of an image and determines if the image is in the expected format. The reader sets the image size, colorspace, and other properties and loads the pixel cache with the pixels. The reader returns a single image or an image sequence (if the format supports multiple images per file), or if an error occurs, an exception and a null image. The writer does the reverse. It takes the image properties and unloads the pixel cache and writes them as required by the image format.</p>
572
573<p>Here is a listing of a sample <a href="../www/source/mgk.c">custom coder</a>. It reads and writes images in the MGK image format which is simply an ID followed by the image width and height followed by the RGB pixel values.</p>
574
575<div class="viewport">
576<pre class="code">
577/*
578 Include declarations.
579*/
580#include "magick/studio.h"
581#include "magick/blob.h"
582#include "magick/blob-private.h"
583#include "magick/colorspace.h"
584#include "magick/exception.h"
585#include "magick/exception-private.h"
586#include "magick/image.h"
587#include "magick/image-private.h"
588#include "magick/list.h"
589#include "magick/magick.h"
590#include "magick/memory_.h"
591#include "magick/monitor.h"
592#include "magick/monitor-private.h"
593#include "magick/quantum-private.h"
594#include "magick/static.h"
595#include "magick/string_.h"
596#include "magick/module.h"
597
598/*
599 Forward declarations.
600*/
601static MagickBooleanType
602 WriteMGKImage(const ImageInfo *,Image *);
603
604/*
605%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
606% %
607% %
608% %
609% I s M G K %
610% %
611% %
612% %
613%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
614%
615% IsMGK() returns MagickTrue if the image format type, identified by the
616% magick string, is MGK.
617%
618% The format of the IsMGK method is:
619%
620% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
621%
622% A description of each parameter follows:
623%
624% o magick: This string is generally the first few bytes of an image file
625% or blob.
626%
627% o length: Specifies the length of the magick string.
628%
629*/
630static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
631{
632 if (length &lt; 7)
633 return(MagickFalse);
634 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
635 return(MagickTrue);
636 return(MagickFalse);
637}
638
639/*
640%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
641% %
642% %
643% %
644% R e a d M G K I m a g e %
645% %
646% %
647% %
648%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
649%
650% ReadMGKImage() reads a MGK image file and returns it. It allocates
651% the memory necessary for the new Image structure and returns a pointer to
652% the new image.
653%
654% The format of the ReadMGKImage method is:
655%
656% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
657%
658% A description of each parameter follows:
659%
660% o image_info: the image info.
661%
662% o exception: return any errors or warnings in this structure.
663%
664*/
665static Image *ReadMGKImage(const ImageInfo *image_info,
666 ExceptionInfo *exception)
667{
668 char
669 buffer[MaxTextExtent];
670
671 Image
672 *image;
673
674 long
675 y;
676
677 MagickBooleanType
678 status;
679
680 register long
681 x;
682
683 register PixelPacket
684 *q;
685
686 register unsigned char
687 *p;
688
689 ssize_t
690 count;
691
692 unsigned char
693 *pixels;
694
695 unsigned long
696 columns,
697 rows;
698
699 /*
700 Open image file.
701 */
702 assert(image_info != (const ImageInfo *) NULL);
703 assert(image_info-&gt;signature == MagickSignature);
704 if (image_info-&gt;debug != MagickFalse)
705 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
706 assert(exception != (ExceptionInfo *) NULL);
707 assert(exception-&gt;signature == MagickSignature);
708 image=AcquireImage(image_info);
709 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
710 if (status == MagickFalse)
711 {
712 image=DestroyImageList(image);
713 return((Image *) NULL);
714 }
715 /*
716 Read MGK image.
717 */
718 (void) ReadBlobString(image,buffer); /* read magic number */
719 if (IsMGK(buffer,7) == MagickFalse)
720 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
721 (void) ReadBlobString(image,buffer);
722 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
723 if (count &lt;= 0)
724 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
725 do
726 {
727 /*
728 Initialize image structure.
729 */
730 image-&gt;columns=columns;
731 image-&gt;rows=rows;
732 image-&gt;depth=8;
733 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
734 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
735 break;
736 /*
737 Convert MGK raster image to pixel packets.
738 */
739 if (SetImageExtent(image,0,0) == MagickFalse)
740 {
741 InheritException(exception,&amp;image-&gt;exception);
742 return(DestroyImageList(image));
743 }
744 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
745 if (pixels == (unsigned char *) NULL)
746 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
747 for (y=0; y &lt; (long) image-&gt;rows; y++)
748 {
749 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
750 if (count != (ssize_t) (3*image-&gt;columns))
751 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
752 p=pixels;
753 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
754 if (q == (PixelPacket *) NULL)
755 break;
756 for (x=0; x &lt; (long) image-&gt;columns; x++)
757 {
758 q-&gt;red=ScaleCharToQuantum(*p++);
759 q-&gt;green=ScaleCharToQuantum(*p++);
760 q-&gt;blue=ScaleCharToQuantum(*p++);
761 q++;
762 }
763 if (SyncAuthenticPixels(image,exception) == MagickFalse)
764 break;
765 if ((image-&gt;previous == (Image *) NULL) &&
766 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
767 break;
768 }
769 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
770 if (EOFBlob(image) != MagickFalse)
771 {
772 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
773 break;
774 }
775 /*
776 Proceed to next image.
777 */
778 if (image_info-&gt;number_scenes != 0)
779 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
780 break;
781 *buffer='\0';
782 (void) ReadBlobString(image,buffer);
783 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
784 if (count != 0)
785 {
786 /*
787 Allocate next image structure.
788 */
789 AcquireNextImage(image_info,image);
790 if (GetNextImageInList(image) == (Image *) NULL)
791 {
792 image=DestroyImageList(image);
793 return((Image *) NULL);
794 }
795 image=SyncNextImageInList(image);
796 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
797 if (status == MagickFalse)
798 break;
799 }
800 } while (count != 0);
801 (void) CloseBlob(image);
802 return(GetFirstImageInList(image));
803}
804
805/*
806%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
807% %
808% %
809% %
810% R e g i s t e r M G K I m a g e %
811% %
812% %
813% %
814%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
815%
816% RegisterMGKImage() adds attributes for the MGK image format to
817% the list of supported formats. The attributes include the image format
818% tag, a method to read and/or write the format, whether the format
819% supports the saving of more than one frame to the same file or blob,
820% whether the format supports native in-memory I/O, and a brief
821% description of the format.
822%
823% The format of the RegisterMGKImage method is:
824%
825% unsigned long RegisterMGKImage(void)
826%
827*/
828ModuleExport unsigned long RegisterMGKImage(void)
829{
830 MagickInfo
831 *entry;
832
833 entry=SetMagickInfo("MGK");
834 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
835 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
836 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
837 entry-&gt;description=ConstantString("MGK");
838 entry-&gt;module=ConstantString("MGK");
839 (void) RegisterMagickInfo(entry);
840 return(MagickImageCoderSignature);
841}
842
843/*
844%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
845% %
846% %
847% %
848% U n r e g i s t e r M G K I m a g e %
849% %
850% %
851% %
852%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
853%
854% UnregisterMGKImage() removes format registrations made by the
855% MGK module from the list of supported formats.
856%
857% The format of the UnregisterMGKImage method is:
858%
859% UnregisterMGKImage(void)
860%
861*/
862ModuleExport void UnregisterMGKImage(void)
863{
864 (void) UnregisterMagickInfo("MGK");
865}
866
867/*
868%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
869% %
870% %
871% %
872% W r i t e M G K I m a g e %
873% %
874% %
875% %
876%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
877%
878% WriteMGKImage() writes an image to a file in red, green, and blue
879% MGK rasterfile format.
880%
881% The format of the WriteMGKImage method is:
882%
883% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
884%
885% A description of each parameter follows.
886%
887% o image_info: the image info.
888%
889% o image: The image.
890%
891*/
892static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
893{
894 char
895 buffer[MaxTextExtent];
896
897 long
898 y;
899
900 MagickBooleanType
901 status;
902
903 MagickOffsetType
904 scene;
905
906 register const PixelPacket
907 *p;
908
909 register long
910 x;
911
912 register unsigned char
913 *q;
914
915 unsigned char
916 *pixels;
917
918 /*
919 Open output image file.
920 */
921 assert(image_info != (const ImageInfo *) NULL);
922 assert(image_info-&gt;signature == MagickSignature);
923 assert(image != (Image *) NULL);
924 assert(image-&gt;signature == MagickSignature);
925 if (image-&gt;debug != MagickFalse)
926 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
927 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
928 if (status == MagickFalse)
929 return(status);
930 scene=0;
931 do
932 {
933 /*
934 Allocate memory for pixels.
935 */
936 if (image-&gt;colorspace != RGBColorspace)
937 (void) SetImageColorspace(image,RGBColorspace);
938 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
939 3UL*sizeof(*pixels));
940 if (pixels == (unsigned char *) NULL)
941 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
942 /*
943 Initialize raster file header.
944 */
945 (void) WriteBlobString(image,"id=mgk\n");
946 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
947 image-&gt;columns,image-&gt;rows);
948 (void) WriteBlobString(image,buffer);
949 for (y=0; y &lt; (long) image-&gt;rows; y++)
950 {
951 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
952 if (p == (const PixelPacket *) NULL)
953 break;
954 q=pixels;
955 for (x=0; x &lt; (long) image-&gt;columns; x++)
956 {
957 *q++=ScaleQuantumToChar(p-&gt;red);
958 *q++=ScaleQuantumToChar(p-&gt;green);
959 *q++=ScaleQuantumToChar(p-&gt;blue);
960 p++;
961 }
962 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
963 if ((image-&gt;previous == (Image *) NULL) &&
964 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
965 break;
966 }
967 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
968 if (GetNextImageInList(image) == (Image *) NULL)
969 break;
970 image=SyncNextImageInList(image);
971 status=SetImageProgress(image,SaveImagesTag,scene,
972 GetImageListLength(image));
973 if (status == MagickFalse)
974 break;
975 scene++;
976 } while (image_info-&gt;adjoin != MagickFalse);
977 (void) CloseBlob(image);
978 return(MagickTrue);
979}
980</pre>
981</div>
982
983<p>To invoke the custom coder from the command line, use these commands:</p>
984
985<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: logo.mgk</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>display logo.mgk</span></p>
986<p>We provide the <a href="ftp://ftp.imagemagick.org/pub/ImageMagick/kits/MagickCoderKit-1.0.0.tar.gz">Magick Coder Kit</a> to help you get started writing your own custom coder.</p>
987
988</div>
989
990<h2><a name="filters"></a>Custom Image Filters</h2>
991<div class="doc-section">
992
993<p>ImageMagick provides a convenient mechanism for adding your own custom image processing algorithms. We call these image filters and they are invoked from the command line with the <a href="../www/command-line-options.html#process">-process</a> option or from the MagickCore API method <a href="../www/api/module.html#ExecuteModuleProcess">ExecuteModuleProcess()</a>.</p>
994
995<p>Here is a listing of a sample <a href="../www/source/analyze.c">custom image filter</a>. It computes a few statistics such as the pixel brightness and saturation mean and standard-deviation.</p>
996
997<div class="viewport">
998<pre class="code">
999#include &lt;stdio.h>
1000#include &lt;stdlib.h>
1001#include &lt;string.h>
1002#include &lt;time.h>
1003#include &lt;assert.h>
1004#include &lt;math.h>
1005#include "magick/MagickCore.h"
1006
1007/*
1008%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1009% %
1010% %
1011% %
1012% a n a l y z e I m a g e %
1013% %
1014% %
1015% %
1016%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1017%
1018% analyzeImage() computes the brightness and saturation mean, standard
1019% deviation, kurtosis and skewness and stores these values as properties of
1020% the image.
1021%
1022% The format of the analyzeImage method is:
1023%
1024% unsigned long analyzeImage(Image *images,const int argc,
1025% const char **argv,ExceptionInfo *exception)
1026%
1027% A description of each parameter follows:
1028%
1029% o image: the address of a structure of type Image.
1030%
1031% o argc: Specifies a pointer to an integer describing the number of
1032% elements in the argument vector.
1033%
1034% o argv: Specifies a pointer to a text array containing the command line
1035% arguments.
1036%
1037% o exception: return any errors or warnings in this structure.
1038%
1039*/
1040ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1041 const char **argv,ExceptionInfo *exception)
1042{
1043 CacheView
1044 *image_view;
1045
1046 char
1047 text[MaxTextExtent];
1048
1049 double
1050 area,
1051 brightness_mean,
1052 brightness_standard_deviation,
1053 brightness_kurtosis,
1054 brightness_skewness,
1055 brightness_sum_x,
1056 brightness_sum_x2,
1057 brightness_sum_x3,
1058 brightness_sum_x4,
1059 saturation_mean,
1060 saturation_standard_deviation,
1061 saturation_kurtosis,
1062 saturation_skewness,
1063 saturation_sum_x,
1064 saturation_sum_x2,
1065 saturation_sum_x3,
1066 saturation_sum_x4;
1067
1068 double
1069 brightness,
1070 hue,
1071 saturation;
1072
1073 Image
1074 *image;
1075
1076 long
1077 y;
1078
1079 register const PixelPacket
1080 *p;
1081
1082 register long
1083 x;
1084
1085 assert(images != (Image **) NULL);
1086 assert(*images != (Image *) NULL);
1087 assert((*images)->signature == MagickSignature);
1088 (void) argc;
1089 (void) argv;
1090 image=(*images);
1091 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1092 {
1093 brightness_sum_x=0.0;
1094 brightness_sum_x2=0.0;
1095 brightness_sum_x3=0.0;
1096 brightness_sum_x4=0.0;
1097 brightness_mean=0.0;
1098 brightness_standard_deviation=0.0;
1099 brightness_kurtosis=0.0;
1100 brightness_skewness=0.0;
1101 saturation_sum_x=0.0;
1102 saturation_sum_x2=0.0;
1103 saturation_sum_x3=0.0;
1104 saturation_sum_x4=0.0;
1105 saturation_mean=0.0;
1106 saturation_standard_deviation=0.0;
1107 saturation_kurtosis=0.0;
1108 saturation_skewness=0.0;
1109 area=0.0;
1110 image_view=AcquireCacheView(image);
1111 for (y=0; y &lt; (long) image-&gt;rows; y++)
1112 {
1113 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1114 if (p == (const PixelPacket *) NULL)
1115 break;
1116 for (x=0; x &lt; (long) image-&gt;columns; x++)
1117 {
1118 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1119 brightness*=QuantumRange;
1120 brightness_sum_x+=brightness;
1121 brightness_sum_x2+=brightness*brightness;
1122 brightness_sum_x3+=brightness*brightness*brightness;
1123 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1124 saturation*=QuantumRange;
1125 saturation_sum_x+=saturation;
1126 saturation_sum_x2+=saturation*saturation;
1127 saturation_sum_x3+=saturation*saturation*saturation;
1128 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1129 area++;
1130 p++;
1131 }
1132 }
1133 image_view=DestroyCacheView(image_view);
1134 if (area &lt;= 0.0)
1135 break;
1136 brightness_mean=brightness_sum_x/area;
1137 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1138 (void) SetImageProperty(image,"filter:brightness:mean",text);
1139 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1140 area*brightness_sum_x/area));
1141 (void) FormatMagickString(text,MaxTextExtent,"%g",
1142 brightness_standard_deviation);
1143 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1144 if (brightness_standard_deviation != 0)
1145 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1146 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1147 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1148 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1149 brightness_standard_deviation*brightness_standard_deviation*
1150 brightness_standard_deviation)-3.0;
1151 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1152 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1153 if (brightness_standard_deviation != 0)
1154 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1155 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1156 brightness_mean)/(brightness_standard_deviation*
1157 brightness_standard_deviation*brightness_standard_deviation);
1158 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1159 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1160 saturation_mean=saturation_sum_x/area;
1161 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1162 (void) SetImageProperty(image,"filter:saturation:mean",text);
1163 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1164 area*saturation_sum_x/area));
1165 (void) FormatMagickString(text,MaxTextExtent,"%g",
1166 saturation_standard_deviation);
1167 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1168 if (saturation_standard_deviation != 0)
1169 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1170 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1171 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1172 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1173 saturation_standard_deviation*saturation_standard_deviation*
1174 saturation_standard_deviation)-3.0;
1175 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1176 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1177 if (saturation_standard_deviation != 0)
1178 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1179 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1180 saturation_mean)/(saturation_standard_deviation*
1181 saturation_standard_deviation*saturation_standard_deviation);
1182 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1183 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1184 }
1185 return(MagickImageFilterSignature);
1186}
1187</pre>
1188</div>
1189
1190<p>To invoke the custom filter from the command line, use this command:</p>
1191
1192<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: -process analyze -verbose info:</span><span class='crtout'>Image: logo: <br/>
1193 Format: LOGO (ImageMagick Logo) <br/>
1194 Class: PseudoClass <br/>
1195 Geometry: 640x480 <br/>
1196 ... <br/>
1197 filter:brightness:kurtosis: 8.98864 <br/>
1198 filter:brightness:mean: 238.096 <br/>
1199 filter:brightness:skewness: -3.04519 <br/>
1200 filter:brightness:standard-deviation: 46.3286 <br/>
1201 filter:saturation:kurtosis: 5.9137 <br/>
1202 filter:saturation:mean: 23.4635 <br/>
1203 filter:saturation:skewness: 2.71874 <br/>
1204 filter:saturation:standard-deviation: 64.7734</span></p>
1205
1206<p>We provide the <a href="ftp://ftp.imagemagick.org/pub/ImageMagick/kits/MagickFilterKit-1.0.0.tar.gz">Magick Filter Kit</a> to help you get started writing your own custom image filter.</p>
1207
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1209
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