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168<div class="main">
169
170
171
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]172<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="#tera-pixel">Large Image Support</a> &bull; <a href="#threads">Threads of Execution</a> &bull; <a href="#distributed">Heterogeneous Distributed Processing</a> &bull; <a href="#coders">Custom Image Coders</a> &bull; <a href="#filters">Custom Image Filters</a>]</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]173
174<div class="doc-section">
175<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>
176</div>
177
178<h2><a name="overview"></a>Architecture Overview</h2>
179<div class="doc-section">
180
181<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>
182
183<ul>
184 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
185 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
186 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
187 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
188 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
189 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
190</ul>
191
192<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>
193
194<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
195
196<ul>
197 <li>one pixel a time (e.g. pixel at location 10,3)</li>
198 <li>a single scanline (e.g. all pixels from row 4)</li>
199 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
200 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
201 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
202 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
203 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
204 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
205 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
206 <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>
207 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]208 <li>all the pixels in memory to take advantage of speed-ups offered by executing in concert across heterogeneous platforms consisting of CPUs, GPUs, and other processors</li>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]209</ul>
210
211<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>
212
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]213<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 (we call these <a href="#authentic-pixels">authentic pixels</a>) 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]214
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]215<p>In addition to pixels, images have a plethora of <a href="#properties">image properties and profiles</a>. Properties include the well known attributes 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]216
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]217<p>ImageMagick consists of more than 400,000 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]218
219</div>
220
221<h2><a name="cache"></a>The Pixel Cache</h2>
222<div class="doc-section">
223
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]224<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 only when you signal your intention to update any of the pixels.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]225
226<h3>Create the Pixel Cache</h3>
227<div class="doc-section">
228
229<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>
230
231<h4>Create an image canvas initialized to the background color:</h4>
232<p class="code">
233 image=AllocateImage(image_info);
234 if (SetImageExtent(image,640,480) == MagickFalse)
235 { /* an exception was thrown */ }
236 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
237 SetImageBackgroundColor(image);
238</p>
239
240<h4>Create an image from a JPEG image on disk:</h4>
241<p class="code"> (void) strcpy(image_info-&gt;filename,"image.jpg"):
242 image=ReadImage(image_info,exception);
243 if (image == (Image *) NULL)
244 { /* an exception was thrown */ }
245</p>
246<h4>Create an image from a memory based image:</h4>
247<p class="code">
248 image=BlobToImage(blob_info,blob,extent,exception);
249 if (image == (Image *) NULL)
250 { /* an exception was thrown */ }
251</p>
252
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]253<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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]254
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]255<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 with the <a href="../www/command-line-options.html#version">&#x2011;version</a> option: </p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]256
cristya20e3f92010-12-13 01:52:32 +0000[diff] [blame^]257<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.6-5 2010-12-01 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]258<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). In most cases, the benefits of the pixel cache typically outweigh any disadvantages.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]259</div>
260
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]261<h3><a name="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]262<div class="doc-section">
263
264<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>
265<ul>
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]266 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify or pixels that lie outside the image region (e.g. pixel @ -1,-3)</li>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]267 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
268 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
269 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
270</ul>
271
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]272<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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]273
274<div class="viewport">
275<pre class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]276 const PixelPacket
277 *p;
278
279 PixelPacket
280 *q;
281
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]282 ssize_t
283 x,
284 y;
285
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]286 destination=CloneImage(source,source->columns,source->rows,MagickTrue,
287 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]288 if (destination == (Image *) NULL)
289 { /* an exception was thrown */ }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]290 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]291 {
292 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
293 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
294 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
295 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]296 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]297 {
298 q-&gt;red=90*p-&gt;red/100;
299 q-&gt;green=90*p-&gt;green/100;
300 q-&gt;blue=90*p-&gt;blue/100;
301 q-&gt;opacity=90*p-&gt;opacity/100;
302 p++;
303 q++;
304 }
305 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
306 break;
307 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]308 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]309 { /* an exception was thrown */ }
310</pre>
311</div>
312
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]313<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. You could use GetAuthenticPixels() to set pixel values but it is slightly more efficient to use QueueAuthenticPixels() instead. Finally, use <a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]314
315<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>
316
317<pre class="code">
318 const IndexPacket
319 *indexes;
320
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]321 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]322 {
323 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
324 if (p == (const PixelPacket *) NULL)
325 break;
326 indexes=GetVirtualIndexes(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]327 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]328 (void) printf("%d\n",indexes[x];
329 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]330 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]331 /* an exception was thrown */
332</pre>
333
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]334<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 at row 479 but if you ask for a scanline at row 480, an exception is returned (rows are numbered starting at 0). GetVirtualPixels() does not have this constraint. For example,</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]335
336<pre class="code">
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]337 p=GetVirtualPixels(source,-3,-3,source-&gt;columns+3,6,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]338</pre>
339
340<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
341</div>
342
343<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
344<div class="doc-section">
345
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]346<p>There are a plethora of image processing algorithms that require a neighborhood of pixels about a pixel of interest. The algorithm typically includes 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]347 <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>
348
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]349<pre class="text" style="font-size: 90%;">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]350 background: the area surrounding the image is the background color
351 black: the area surrounding the image is black
352 checker-tile: alternate squares with image and background color
353 dither: non-random 32x32 dithered pattern
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]354 edge: extend the edge pixel toward infinity (default)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]355 gray: the area surrounding the image is gray
356 horizontal-tile: horizontally tile the image, background color above/below
357 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
358 mirror: mirror tile the image
359 random: choose a random pixel from the image
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]360 tile: tile the image
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]361 transparent: the area surrounding the image is transparent blackness
362 vertical-tile: vertically tile the image, sides are background color
363 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
364 white: the area surrounding the image is white
365</pre>
366
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]367</div>
368
369<h3>Cache Storage and Resource Requirements</h3>
370<div class="doc-section">
371
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]372<p>Recall 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 are using the Q16 version of ImageMagick, the pixel cache consumes image <em>width * height * bit-depth / 8 * channels</em> bytes or approximately 2.3 mebibytes (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 gibibytes 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]373
374<dl class="doc">
375 <dt class="doc">files</dt>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]376 <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 without a speed penalty due to repeated open/close calls.</dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]377 <dt class="doc">area</dt>
378 <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>
379 <dt class="doc">memory</dt>
380 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
381 <dt class="doc">map</dt>
382 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
383 <dt class="doc">disk</dt>
384 <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>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]385 <dt class="doc">thread</dt>
386 <dd>maximum number of threads that are permitted to run in parallel.</dd>
387 <dt class="doc">time</dt>
388 <dd>maximum number of seconds that the process is permitted to execute. When this limit is exceeded, an exception is thrown and processing stops.</dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]389</dl>
390
391<p>To determine the current setting of these limits, use this command:</p>
392
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]393<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
394-------------------------------------------------------------------------------
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]395 768 1.0386GB 3.8692GiB 7.7384GiB unlimited 4 unlimited
396</pre
397></span></p>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]398<p>You can set these limits either as a <a href="../www/resources.html#configure">policy</a> (see <a href="../www/source/policy.xml">policy.xml</a>), with an <a href="../www/resources.html#environment">environment variable</a>, with the <a href="../www/command-line-options.html#limit">-limit</a> command line option, or with 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 mebibytes and a map limit of 256 mebibytes 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]399
400<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>
401</div>
402
403<h3>Cache Views</h3>
404<div class="doc-section">
405
406<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>
407
408<pre class="code">
409 CacheView
410 *view_1,
411 *view_2;
412
413 view_1=OpenCacheView(source);
414 view_2=OpenCacheView(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]415 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]416 {
417 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]418 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,
419 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]420 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
421 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]422 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]423 {
424 /* do something with u &amp; v here */
425 }
426 }
427 view_1=CloseCacheView(view_1);
428 view_2=CloseCacheView(view_2);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]429 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]430 { /* an exception was thrown */ }
431</pre>
432</div>
433
434<h3>Magick Persistent Cache Format</h3>
435<div class="doc-section">
436
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]437<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 raw 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>
cristy5063d812010-10-19 16:28:10 +0000[diff] [blame]438<p>The most efficient use of MPC image files is a write-once, read-many-times pattern. For example, your workflow requires extracting random blocks of pixels from the source image. Rather than re-reading and possibly decompressing the source image each time, we use MPC and map the image directly to memory.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]439</div>
440
441<h3>Best Practices</h3>
442<div class="doc-section">
443
444<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>
445
446<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>
447
448<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>
449
450<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>
451
452<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>
453
454<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>
455
456<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>
457
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]458<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 by default so some algorithms may perform differently than the non-HDRI version.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]459
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]460<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_TEMPORARY_PATH environment variable. For example,</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]461
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]462<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>export MAGICK_TEMPORARY_PATH=/data/magick</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]463
464<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>
465
466<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>
467<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>
468</div>
469
470</div>
471
472<h2><a name="stream"></a>Streaming Pixels</h2>
473<div class="doc-section">
474
475<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>
476
477<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>
478
479<pre class="code">
480static size_t StreamHandler(const Image *image,const void *pixels,
481 const size_t columns)
482{
483 /* process pixels here */
484 return(columns);
485}
486
487...
488/* invoke the pixel stream here */
489image=ReadStream(image_info,&amp;StreamHandler,exception);
490</pre>
491
492<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>
493
494</div>
495
496<h2><a name="properties"></a>Image Properties and Profiles</h2>
497<div class="doc-section">
498
499<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>
500
501<pre class="code">
502 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
503</pre>
504
505<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>
506
507<pre class="code">
508 const char
509 *comment;
510
511 (void) SetImageProperty(image,"comment","This space for rent");
512 comment=GetImageProperty(image,"comment");
513 if (comment == (const char *) NULL)
514 (void) printf("Image comment: %s\n",comment);
515</pre>
516
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]517<p>ImageMagick supports artifacts with the GetImageArtifact() and SetImageArtifact() methods. Artifacts are stealth properties that are not exported to image formats (e.g. PNG).</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]518
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]519<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>
520
521<pre class="code">
522 StringInfo
523 *profile;
524
525 profile=AcquireStringInfo(length);
526 SetStringInfoDatum(profile,my_exif_profile);
527 (void) SetImageProfile(image,"EXIF",profile);
528 DestroyStringInfo(profile);
529 profile=GetImageProfile(image,"EXIF");
530 if (profile != (StringInfo *) NULL)
531 (void) PrintStringInfo(stdout,"EXIF",profile);
532</pre>
533
534</div>
535
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]536<h2><a name="tera-pixel"></a>Large Image Support</h2>
537<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]538<p>ImageMagick can read, process, or write mega-, giga-, or tera-pixel image sizes. An image width or height can range from 1 to 2 giga-pixels on a 32 bit OS and up to 9 exa-pixels on a 64-bit OS. Note, that some image formats have restrictions on image size. For example, Photoshop images are limited to 300,000 pixels for width or height. Here we resize an image to a quarter million pixels square:</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]539
540<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: -resize 250000x250000 logo.miff</span></p>
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]541<p>For large images, ImageMagick will likely create a pixel cache on disk. Make sure you have plenty of temporary disk space. If your default temporary disk partition is too small, tell ImageMagick to use another partition with plenty of free space. For example:</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]542
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]543<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp logo: \ <br/> -resize 250000x250000 logo.miff</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]544<p>To ensure large images do not consume all the memory on your system, force the image pixels to memory-mapped disk with resource limits:</p>
545
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]546<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit memory 16mb \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]547<p>Here we force all image pixels to disk:</p>
548
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]549<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
cristybac7a162010-06-15 19:57:29 +0000[diff] [blame]550<p>Caching pixels to disk is about 1000 times slower than memory. Expect long run times when processing large images on disk with ImageMagick. You can monitor progress with this command:</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]551
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]552<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -monitor -define registry:temporary-path=/data/tmp -limit area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p></div>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]553
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]554<h2><a name="threads"></a>Threads of Execution</h2>
555<div class="doc-section">
556
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]557<p>Many of ImageMagick's internal algorithms are threaded to take advantage of speed-ups offered by the multicore processor chips. 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 with the exception of an OpenMP parallel section. 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]558
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]559<p>Here is an example of how ImageMagick can take advantage of threads of execution with the <a href="http://en.wikipedia.org/wiki/OpenMP">OpenMP</a> programming paradigm:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]560
561<div class="viewport">
562<pre class="code">
563{
564 CacheView
565 *image_view;
566
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]567 MagickBooleanType
568 status;
569
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]570 ssize_t
571 y;
572
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]573 status=MagickTrue;
574 image_view=AcquireCacheView(image);
575 #pragma omp parallel for schedule(dynamic,4) shared(status)
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]576 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]577 {
578 register IndexPacket
579 *indexes;
580
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]581 register PixelPacket
582 *q;
583
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]584 register ssize_t
585 x;
586
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]587 if (status == MagickFalse)
588 continue;
589 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
590 if (q == (PixelPacket *) NULL)
591 {
592 status=MagickFalse;
593 continue;
594 }
595 indexes=GetCacheViewAuthenticIndexQueue(image_view);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]596 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]597 {
598 q-&gt;red= ...
599 q-&gt;green= ...
600 q-&gt;blue= ...
601 q-&gt;opacity= ...
602 if (indexes != (IndexPacket *) NULL)
603 indexes[x]= ...
604 q++;
605 }
606 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
607 status=MagickFalse;
608 }
609 image_view=DestroyCacheView(image_view);
610 if (status == MagickFalse)
611 perror("something went wrong");
612}
613</pre>
614</div>
615
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]616
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]617<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>
618
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]619<p><a href="../www/api/wand-view.html">MagickWand</a> supports wand views. A view iterates over the entire, or portion, of the image in parallel and for each row of pixels, it invokes a callback method you provide. This limits most of your parallel programming activity to just that one module. There are similar methods in <a href="../www/api/image-view.html">MagickCore</a>. For an example, see the same sigmoidal contrast algorithm implemented in both <a href="../www/magick-wand.html#wand-view">MagickWand</a> and <a href="../www/magick-core.html#image-view">MagickCore</a>.</p>
cristyfe7ce342010-06-22 15:41:50 +0000[diff] [blame]620
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]621<p>In most circumstances, the default number of threads is set to the number of processor cores on your system for optimal performance. However, if your system is hyperthreaded or if you are running on a virtual host and only a subset of the processors are available to your server instance, you might get an increase in performance by setting the thread <a href="../www/resources.html#configure">policy</a> or the <a href="../www/resources.html#environment">MAGICK_THREAD_LIMIT</a> environment variable. For example, your virtual host has 8 processors but only 2 are assigned to your server instance. The default of 8 threads can cause severe performance problems. One solution is to limit the number of threads to the available processors in your <a href="../www/source/policy.xml">policy.xml</a> configuration file:</p>
cristyce66ab12010-10-21 23:36:32 +0000[diff] [blame]622
623<pre class="text">
624 &lt;policy domain="resource" name="thread" value="2"/>
625</pre>
626
627<p>Or suppose your 12 core hyperthreaded computer defaults to 24 threads. Set the MAGICK_THREAD_LIMIT environment variable and you will likely get improved performance:</p>
628
629<pre class="text">
630 export MAGICK_THREAD_LIMIT=12
631</pre>
632
633<p>The OpenMP committee has not defined the behavior of mixing OpenMP with other threading models such as Posix threads. However, using modern releases of Linux, OpenMP and Posix threads appear to interoperate without complaint. If you want to use Posix threads from a program module that calls one of the ImageMagick application programming interfaces (e.g. MagickCore, MagickWand, Magick++, etc.) from Mac OS X or an older Linux release, you may need to disable OpenMP support within ImageMagick. Add the <kbd>--disable-openmp</kbd> option to the configure script command line and rebuild and reinstall ImageMagick.</p>
634
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]635</div>
636
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]637<h2><a name="distributed"></a>Heterogeneous Distributed Processing</h2>
638<div class="doc-section">
639<p>ImageMagick includes support for heterogeneous distributed processing with the <a href="http://en.wikipedia.org/wiki/OpenCL">OpenCL</a> framework. OpenCL kernels within ImageMagick permit image processing algorithms to execute across heterogeneous platforms consisting of CPUs, GPUs, and other processors. Depending on your platform, speed-ups can be an order of magnitude faster than the traditional single CPU.</p>
640
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]641<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]642
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]643<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
644<p>If so, run this command to realize a significant speed-up for image convolution:</p>
645
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]646<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.png convolve '-1, -1, -1, -1, 9, -1, -1, -1, -1' \ <br/> convolve.png</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]647<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
648
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]649<p>Here is an example OpenCL kernel that convolves an image:</p>
650
651<div class="viewport">
652<pre class="code">
653static inline long ClampToCanvas(const long offset,const ulong range)
654{
655 if (offset &lt; 0L)
656 return(0L);
657 if (offset >= range)
658 return((long) (range-1L));
659 return(offset);
660}
661
662static inline CLQuantum ClampToQuantum(const double value)
663{
664 if (value &lt; 0.0)
665 return((CLQuantum) 0);
666 if (value >= (double) QuantumRange)
667 return((CLQuantum) QuantumRange);
668 return((CLQuantum) (value+0.5));
669}
670
671__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
672 const ulong width,const ulong height,__global CLPixelType *destination)
673{
674 const ulong columns = get_global_size(0);
675 const ulong rows = get_global_size(1);
676
677 const long x = get_global_id(0);
678 const long y = get_global_id(1);
679
680 const double scale = (1.0/QuantumRange);
681 const long mid_width = (width-1)/2;
682 const long mid_height = (height-1)/2;
683 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
684 double gamma = 0.0;
685 register ulong i = 0;
686
687 for (long v=(-mid_height); v &lt;= mid_height; v++)
688 {
689 for (long u=(-mid_width); u &lt;= mid_width; u++)
690 {
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]691 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,
692 columns);
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]693 const double alpha=scale*(QuantumRange-source[index].w);
694 sum.x+=alpha*filter[i]*source[index].x;
695 sum.y+=alpha*filter[i]*source[index].y;
696 sum.z+=alpha*filter[i]*source[index].z;
697 sum.w+=filter[i]*source[index].w;
698 gamma+=alpha*filter[i];
699 i++;
700 }
701 }
702
703 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
704 const ulong index=y*columns+x;
705 destination[index].x=ClampToQuantum(gamma*sum.x);
706 destination[index].y=ClampToQuantum(gamma*sum.y);
707 destination[index].z=ClampToQuantum(gamma*sum.z);
708 destination[index].w=ClampToQuantum(sum.w);
709};
710</pre>
711</div>
712
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]713<p>See <a href="http://trac.imagemagick.org/browser/ImageMagick/trunk/magick/accelerate.c">magick/accelerate.c</a> for a complete implementation of image convolution with an OpenCL kernel.</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]714
715</div>
716
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]717<h2><a name="coders"></a>Custom Image Coders</h2>
718<div class="doc-section">
719
720<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>
721
722<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>
723
724<div class="viewport">
725<pre class="code">
726/*
727 Include declarations.
728*/
729#include "magick/studio.h"
730#include "magick/blob.h"
731#include "magick/blob-private.h"
732#include "magick/colorspace.h"
733#include "magick/exception.h"
734#include "magick/exception-private.h"
735#include "magick/image.h"
736#include "magick/image-private.h"
737#include "magick/list.h"
738#include "magick/magick.h"
739#include "magick/memory_.h"
740#include "magick/monitor.h"
741#include "magick/monitor-private.h"
742#include "magick/quantum-private.h"
743#include "magick/static.h"
744#include "magick/string_.h"
745#include "magick/module.h"
746
747/*
748 Forward declarations.
749*/
750static MagickBooleanType
751 WriteMGKImage(const ImageInfo *,Image *);
752
753/*
754%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
755% %
756% %
757% %
758% I s M G K %
759% %
760% %
761% %
762%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
763%
764% IsMGK() returns MagickTrue if the image format type, identified by the
765% magick string, is MGK.
766%
767% The format of the IsMGK method is:
768%
769% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
770%
771% A description of each parameter follows:
772%
773% o magick: This string is generally the first few bytes of an image file
774% or blob.
775%
776% o length: Specifies the length of the magick string.
777%
778*/
779static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
780{
781 if (length &lt; 7)
782 return(MagickFalse);
783 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
784 return(MagickTrue);
785 return(MagickFalse);
786}
787
788/*
789%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
790% %
791% %
792% %
793% R e a d M G K I m a g e %
794% %
795% %
796% %
797%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
798%
799% ReadMGKImage() reads a MGK image file and returns it. It allocates
800% the memory necessary for the new Image structure and returns a pointer to
801% the new image.
802%
803% The format of the ReadMGKImage method is:
804%
805% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
806%
807% A description of each parameter follows:
808%
809% o image_info: the image info.
810%
811% o exception: return any errors or warnings in this structure.
812%
813*/
814static Image *ReadMGKImage(const ImageInfo *image_info,
815 ExceptionInfo *exception)
816{
817 char
818 buffer[MaxTextExtent];
819
820 Image
821 *image;
822
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]823 MagickBooleanType
824 status;
825
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]826 register PixelPacket
827 *q;
828
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]829 register size_t
830 x;
831
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]832 register unsigned char
833 *p;
834
835 ssize_t
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]836 count,
837 y;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]838
839 unsigned char
840 *pixels;
841
842 unsigned long
843 columns,
844 rows;
845
846 /*
847 Open image file.
848 */
849 assert(image_info != (const ImageInfo *) NULL);
850 assert(image_info-&gt;signature == MagickSignature);
851 if (image_info-&gt;debug != MagickFalse)
852 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
853 assert(exception != (ExceptionInfo *) NULL);
854 assert(exception-&gt;signature == MagickSignature);
855 image=AcquireImage(image_info);
856 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
857 if (status == MagickFalse)
858 {
859 image=DestroyImageList(image);
860 return((Image *) NULL);
861 }
862 /*
863 Read MGK image.
864 */
865 (void) ReadBlobString(image,buffer); /* read magic number */
866 if (IsMGK(buffer,7) == MagickFalse)
867 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
868 (void) ReadBlobString(image,buffer);
869 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
870 if (count &lt;= 0)
871 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
872 do
873 {
874 /*
875 Initialize image structure.
876 */
877 image-&gt;columns=columns;
878 image-&gt;rows=rows;
879 image-&gt;depth=8;
880 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
881 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
882 break;
883 /*
884 Convert MGK raster image to pixel packets.
885 */
886 if (SetImageExtent(image,0,0) == MagickFalse)
887 {
888 InheritException(exception,&amp;image-&gt;exception);
889 return(DestroyImageList(image));
890 }
891 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
892 if (pixels == (unsigned char *) NULL)
893 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]894 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]895 {
896 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
897 if (count != (ssize_t) (3*image-&gt;columns))
898 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
899 p=pixels;
900 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
901 if (q == (PixelPacket *) NULL)
902 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]903 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]904 {
905 q-&gt;red=ScaleCharToQuantum(*p++);
906 q-&gt;green=ScaleCharToQuantum(*p++);
907 q-&gt;blue=ScaleCharToQuantum(*p++);
908 q++;
909 }
910 if (SyncAuthenticPixels(image,exception) == MagickFalse)
911 break;
912 if ((image-&gt;previous == (Image *) NULL) &&
913 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
914 break;
915 }
916 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
917 if (EOFBlob(image) != MagickFalse)
918 {
919 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
920 break;
921 }
922 /*
923 Proceed to next image.
924 */
925 if (image_info-&gt;number_scenes != 0)
926 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
927 break;
928 *buffer='\0';
929 (void) ReadBlobString(image,buffer);
930 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
931 if (count != 0)
932 {
933 /*
934 Allocate next image structure.
935 */
936 AcquireNextImage(image_info,image);
937 if (GetNextImageInList(image) == (Image *) NULL)
938 {
939 image=DestroyImageList(image);
940 return((Image *) NULL);
941 }
942 image=SyncNextImageInList(image);
943 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
944 if (status == MagickFalse)
945 break;
946 }
947 } while (count != 0);
948 (void) CloseBlob(image);
949 return(GetFirstImageInList(image));
950}
951
952/*
953%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
954% %
955% %
956% %
957% R e g i s t e r M G K I m a g e %
958% %
959% %
960% %
961%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
962%
963% RegisterMGKImage() adds attributes for the MGK image format to
964% the list of supported formats. The attributes include the image format
965% tag, a method to read and/or write the format, whether the format
966% supports the saving of more than one frame to the same file or blob,
967% whether the format supports native in-memory I/O, and a brief
968% description of the format.
969%
970% The format of the RegisterMGKImage method is:
971%
972% unsigned long RegisterMGKImage(void)
973%
974*/
975ModuleExport unsigned long RegisterMGKImage(void)
976{
977 MagickInfo
978 *entry;
979
980 entry=SetMagickInfo("MGK");
981 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
982 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
983 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
984 entry-&gt;description=ConstantString("MGK");
985 entry-&gt;module=ConstantString("MGK");
986 (void) RegisterMagickInfo(entry);
987 return(MagickImageCoderSignature);
988}
989
990/*
991%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
992% %
993% %
994% %
995% U n r e g i s t e r M G K I m a g e %
996% %
997% %
998% %
999%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1000%
1001% UnregisterMGKImage() removes format registrations made by the
1002% MGK module from the list of supported formats.
1003%
1004% The format of the UnregisterMGKImage method is:
1005%
1006% UnregisterMGKImage(void)
1007%
1008*/
1009ModuleExport void UnregisterMGKImage(void)
1010{
1011 (void) UnregisterMagickInfo("MGK");
1012}
1013
1014/*
1015%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1016% %
1017% %
1018% %
1019% W r i t e M G K I m a g e %
1020% %
1021% %
1022% %
1023%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1024%
1025% WriteMGKImage() writes an image to a file in red, green, and blue
1026% MGK rasterfile format.
1027%
1028% The format of the WriteMGKImage method is:
1029%
1030% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1031%
1032% A description of each parameter follows.
1033%
1034% o image_info: the image info.
1035%
1036% o image: The image.
1037%
1038*/
1039static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1040{
1041 char
1042 buffer[MaxTextExtent];
1043
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1044 MagickBooleanType
1045 status;
1046
1047 MagickOffsetType
1048 scene;
1049
1050 register const PixelPacket
1051 *p;
1052
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1053 register ssize_t
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1054 x;
1055
1056 register unsigned char
1057 *q;
1058
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1059 ssize_t
1060 y;
1061
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1062 unsigned char
1063 *pixels;
1064
1065 /*
1066 Open output image file.
1067 */
1068 assert(image_info != (const ImageInfo *) NULL);
1069 assert(image_info-&gt;signature == MagickSignature);
1070 assert(image != (Image *) NULL);
1071 assert(image-&gt;signature == MagickSignature);
1072 if (image-&gt;debug != MagickFalse)
1073 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1074 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1075 if (status == MagickFalse)
1076 return(status);
1077 scene=0;
1078 do
1079 {
1080 /*
1081 Allocate memory for pixels.
1082 */
1083 if (image-&gt;colorspace != RGBColorspace)
1084 (void) SetImageColorspace(image,RGBColorspace);
1085 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1086 3UL*sizeof(*pixels));
1087 if (pixels == (unsigned char *) NULL)
1088 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1089 /*
1090 Initialize raster file header.
1091 */
1092 (void) WriteBlobString(image,"id=mgk\n");
1093 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1094 image-&gt;columns,image-&gt;rows);
1095 (void) WriteBlobString(image,buffer);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1096 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1097 {
1098 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1099 if (p == (const PixelPacket *) NULL)
1100 break;
1101 q=pixels;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1102 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1103 {
1104 *q++=ScaleQuantumToChar(p-&gt;red);
1105 *q++=ScaleQuantumToChar(p-&gt;green);
1106 *q++=ScaleQuantumToChar(p-&gt;blue);
1107 p++;
1108 }
1109 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
1110 if ((image-&gt;previous == (Image *) NULL) &&
1111 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1112 break;
1113 }
1114 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1115 if (GetNextImageInList(image) == (Image *) NULL)
1116 break;
1117 image=SyncNextImageInList(image);
1118 status=SetImageProgress(image,SaveImagesTag,scene,
1119 GetImageListLength(image));
1120 if (status == MagickFalse)
1121 break;
1122 scene++;
1123 } while (image_info-&gt;adjoin != MagickFalse);
1124 (void) CloseBlob(image);
1125 return(MagickTrue);
1126}
1127</pre>
1128</div>
1129
1130<p>To invoke the custom coder from the command line, use these commands:</p>
1131
1132<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>
1133<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>
1134
1135</div>
1136
1137<h2><a name="filters"></a>Custom Image Filters</h2>
1138<div class="doc-section">
1139
1140<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>
1141
1142<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>
1143
1144<div class="viewport">
1145<pre class="code">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1146#include &lt;stdio.h&gt;
1147#include &lt;stdlib.h&gt;
1148#include &lt;string.h&gt;
1149#include &lt;time.h&gt;
1150#include &lt;assert.h&gt;
1151#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1152#include "magick/MagickCore.h"
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1153
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1154/*
1155%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1156% %
1157% %
1158% %
1159% a n a l y z e I m a g e %
1160% %
1161% %
1162% %
1163%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1164%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1165% analyzeImage() computes the brightness and saturation mean, standard
1166% deviation, kurtosis and skewness and stores these values as attributes
1167% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1168%
1169% The format of the analyzeImage method is:
1170%
1171% unsigned long analyzeImage(Image *images,const int argc,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1172% char **argv,ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1173%
1174% A description of each parameter follows:
1175%
1176% o image: the address of a structure of type Image.
1177%
1178% o argc: Specifies a pointer to an integer describing the number of
1179% elements in the argument vector.
1180%
1181% o argv: Specifies a pointer to a text array containing the command line
1182% arguments.
1183%
1184% o exception: return any errors or warnings in this structure.
1185%
1186*/
1187ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1188 const char **argv,ExceptionInfo *exception)
1189{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1190 char
1191 text[MaxTextExtent];
1192
1193 double
1194 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1195 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1196 brightness_mean,
1197 brightness_standard_deviation,
1198 brightness_kurtosis,
1199 brightness_skewness,
1200 brightness_sum_x,
1201 brightness_sum_x2,
1202 brightness_sum_x3,
1203 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1204 hue,
1205 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1206 saturation_mean,
1207 saturation_standard_deviation,
1208 saturation_kurtosis,
1209 saturation_skewness,
1210 saturation_sum_x,
1211 saturation_sum_x2,
1212 saturation_sum_x3,
1213 saturation_sum_x4;
1214
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1215 Image
1216 *image;
1217
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1218 assert(images != (Image **) NULL);
1219 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1220 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1221 (void) argc;
1222 (void) argv;
1223 image=(*images);
1224 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1225 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1226 CacheView
1227 *image_view;
1228
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1229 MagickBooleanType
1230 status;
1231
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1232 ssize_t
1233 y;
1234
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1235 brightness_sum_x=0.0;
1236 brightness_sum_x2=0.0;
1237 brightness_sum_x3=0.0;
1238 brightness_sum_x4=0.0;
1239 brightness_mean=0.0;
1240 brightness_standard_deviation=0.0;
1241 brightness_kurtosis=0.0;
1242 brightness_skewness=0.0;
1243 saturation_sum_x=0.0;
1244 saturation_sum_x2=0.0;
1245 saturation_sum_x3=0.0;
1246 saturation_sum_x4=0.0;
1247 saturation_mean=0.0;
1248 saturation_standard_deviation=0.0;
1249 saturation_kurtosis=0.0;
1250 saturation_skewness=0.0;
1251 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1252 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1253 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1254#if defined(MAGICKCORE_OPENMP_SUPPORT)
1255 #pragma omp parallel for schedule(dynamic,4) shared(status)
1256#endif
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1257 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1258 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1259 register const PixelPacket
1260 *p;
1261
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1262 register ssize_t
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1263 x;
1264
1265 if (status == MagickFalse)
1266 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1267 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1268 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1269 {
1270 status=MagickFalse;
1271 continue;
1272 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1273 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1274 {
1275 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1276 brightness*=QuantumRange;
1277 brightness_sum_x+=brightness;
1278 brightness_sum_x2+=brightness*brightness;
1279 brightness_sum_x3+=brightness*brightness*brightness;
1280 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1281 saturation*=QuantumRange;
1282 saturation_sum_x+=saturation;
1283 saturation_sum_x2+=saturation*saturation;
1284 saturation_sum_x3+=saturation*saturation*saturation;
1285 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1286 area++;
1287 p++;
1288 }
1289 }
1290 image_view=DestroyCacheView(image_view);
1291 if (area &lt;= 0.0)
1292 break;
1293 brightness_mean=brightness_sum_x/area;
1294 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1295 (void) SetImageProperty(image,"filter:brightness:mean",text);
1296 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1297 area*brightness_sum_x/area));
1298 (void) FormatMagickString(text,MaxTextExtent,"%g",
1299 brightness_standard_deviation);
1300 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1301 if (brightness_standard_deviation != 0)
1302 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1303 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1304 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1305 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1306 brightness_standard_deviation*brightness_standard_deviation*
1307 brightness_standard_deviation)-3.0;
1308 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1309 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1310 if (brightness_standard_deviation != 0)
1311 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1312 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1313 brightness_mean)/(brightness_standard_deviation*
1314 brightness_standard_deviation*brightness_standard_deviation);
1315 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1316 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1317 saturation_mean=saturation_sum_x/area;
1318 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1319 (void) SetImageProperty(image,"filter:saturation:mean",text);
1320 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1321 area*saturation_sum_x/area));
1322 (void) FormatMagickString(text,MaxTextExtent,"%g",
1323 saturation_standard_deviation);
1324 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1325 if (saturation_standard_deviation != 0)
1326 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1327 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1328 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1329 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1330 saturation_standard_deviation*saturation_standard_deviation*
1331 saturation_standard_deviation)-3.0;
1332 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1333 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1334 if (saturation_standard_deviation != 0)
1335 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1336 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1337 saturation_mean)/(saturation_standard_deviation*
1338 saturation_standard_deviation*saturation_standard_deviation);
1339 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1340 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1341 }
1342 return(MagickImageFilterSignature);
1343}
1344</pre>
1345</div>
1346
1347<p>To invoke the custom filter from the command line, use this command:</p>
1348
1349<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/>
1350 Format: LOGO (ImageMagick Logo) <br/>
1351 Class: PseudoClass <br/>
1352 Geometry: 640x480 <br/>
1353 ... <br/>
1354 filter:brightness:kurtosis: 8.98864 <br/>
1355 filter:brightness:mean: 238.096 <br/>
1356 filter:brightness:skewness: -3.04519 <br/>
1357 filter:brightness:standard-deviation: 46.3286 <br/>
1358 filter:saturation:kurtosis: 5.9137 <br/>
1359 filter:saturation:mean: 23.4635 <br/>
1360 filter:saturation:skewness: 2.71874 <br/>
1361 filter:saturation:standard-deviation: 64.7734</span></p>
1362
1363<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>
1364
1365</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1366
1367</div>
1368
1369<div id="linkbar">
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]1370 <span id="linkbar-west">&nbsp;</span>
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1372 <a href="http://www.imagemagick.org/discourse-server/">Discourse Server</a> &bull;
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1375 <span id="linkbar-east">&nbsp;</span>
1376 </div>
1377 <div class="footer">
cristy7e41fe82010-12-04 23:12:08 +0000[diff] [blame]1378 <span id="footer-west">&copy; 1999-2011 ImageMagick Studio LLC</span>
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