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178
179<div class="main">
180
181
182
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]183<h1>The <em>Magick</em> Behind ImageMagick</h1>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]184<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]185
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]186
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]187<div class="doc-section">
188<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>
189</div>
190
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]191<h2><a id="overview"></a>Architecture Overview</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]192<div class="doc-section">
193
194<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>
195
196<ul>
197 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
198 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
199 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
200 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
201 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
202 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
203</ul>
204
205<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>
206
207<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
208
209<ul>
210 <li>one pixel a time (e.g. pixel at location 10,3)</li>
211 <li>a single scanline (e.g. all pixels from row 4)</li>
212 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
213 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
214 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
215 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
216 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
217 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
218 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
219 <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>
220 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]221 <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]222</ul>
223
224<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>
225
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]226<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]227
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]228<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]229
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]230<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]231
232</div>
233
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]234<h2><a id="cache"></a>The Pixel Cache</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]235<div class="doc-section">
236
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]237<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]238
239<h3>Create the Pixel Cache</h3>
240<div class="doc-section">
241
242<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>
243
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]244<dl>
245<dt>Create an image canvas initialized to the background color:</dt>
246<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]247 image=AllocateImage(image_info);
248 if (SetImageExtent(image,640,480) == MagickFalse)
249 { /* an exception was thrown */ }
250 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
251 SetImageBackgroundColor(image);
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]252</p></dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]253
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]254<dt>Create an image from a JPEG image on disk:</dt>
255<dd><p class="code">
256 (void) strcpy(image_info-&gt;filename,"image.jpg"):
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]257 image=ReadImage(image_info,exception);
258 if (image == (Image *) NULL)
259 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]260</p></dd>
261<dt>Create an image from a memory based image:</dt>
262<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]263 image=BlobToImage(blob_info,blob,extent,exception);
264 if (image == (Image *) NULL)
265 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]266</p></dd>
267</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]268
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]269<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]270
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]271<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]272
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame^]273<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.7-2 2010-21-21 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]274<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]275</div>
276
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]277<h3><a id="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]278<div class="doc-section">
279
280<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>
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]281<dl>
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]282 <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]283 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
284 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
285 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]286</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]287
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]288<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]289
290<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]291 const PixelPacket
292 *p;
293
294 PixelPacket
295 *q;
296
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]297 ssize_t
298 x,
299 y;
300
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]301 destination=CloneImage(source,source->columns,source->rows,MagickTrue,
302 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]303 if (destination == (Image *) NULL)
304 { /* an exception was thrown */ }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]305 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]306 {
307 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
308 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
309 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
310 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]311 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]312 {
313 q-&gt;red=90*p-&gt;red/100;
314 q-&gt;green=90*p-&gt;green/100;
315 q-&gt;blue=90*p-&gt;blue/100;
316 q-&gt;opacity=90*p-&gt;opacity/100;
317 p++;
318 q++;
319 }
320 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
321 break;
322 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]323 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]324 { /* an exception was thrown */ }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]325</div>
326
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]327<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]328
329<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>
330
331<pre class="code">
332 const IndexPacket
333 *indexes;
334
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]335 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]336 {
337 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
338 if (p == (const PixelPacket *) NULL)
339 break;
340 indexes=GetVirtualIndexes(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]341 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]342 (void) printf("%d\n",indexes[x];
343 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]344 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]345 /* an exception was thrown */
346</pre>
347
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]348<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]349
350<pre class="code">
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]351 p=GetVirtualPixels(source,-3,-3,source-&gt;columns+3,6,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]352</pre>
353
354<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
355</div>
356
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]357<h3><a id="virtual-pixels"></a>Virtual Pixels</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]358<div class="doc-section">
359
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]360<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]361 <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>
362
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]363<pre class="text" style="font-size: 90%;">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]364 background: the area surrounding the image is the background color
365 black: the area surrounding the image is black
366 checker-tile: alternate squares with image and background color
367 dither: non-random 32x32 dithered pattern
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]368 edge: extend the edge pixel toward infinity (default)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]369 gray: the area surrounding the image is gray
370 horizontal-tile: horizontally tile the image, background color above/below
371 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
372 mirror: mirror tile the image
373 random: choose a random pixel from the image
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]374 tile: tile the image
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]375 transparent: the area surrounding the image is transparent blackness
376 vertical-tile: vertically tile the image, sides are background color
377 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
378 white: the area surrounding the image is white
379</pre>
380
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]381</div>
382
383<h3>Cache Storage and Resource Requirements</h3>
384<div class="doc-section">
385
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]386<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]387
388<dl class="doc">
389 <dt class="doc">files</dt>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]390 <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]391 <dt class="doc">area</dt>
392 <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>
393 <dt class="doc">memory</dt>
394 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
395 <dt class="doc">map</dt>
396 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
397 <dt class="doc">disk</dt>
398 <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]399 <dt class="doc">thread</dt>
400 <dd>maximum number of threads that are permitted to run in parallel.</dd>
401 <dt class="doc">time</dt>
402 <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]403</dl>
404
405<p>To determine the current setting of these limits, use this command:</p>
406
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]407<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span></p><pre class="text">
408File Area Memory Map Disk Thread Time
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]409-------------------------------------------------------------------------------
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]410 768 1.0386GB 3.8692GiB 7.7384GiB unlimited 4 unlimited
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]411</pre>
412
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]413<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]414
415<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>
416</div>
417
418<h3>Cache Views</h3>
419<div class="doc-section">
420
421<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>
422
423<pre class="code">
424 CacheView
425 *view_1,
426 *view_2;
427
428 view_1=OpenCacheView(source);
429 view_2=OpenCacheView(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]430 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]431 {
432 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]433 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,
434 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]435 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
436 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]437 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]438 {
439 /* do something with u &amp; v here */
440 }
441 }
442 view_1=CloseCacheView(view_1);
443 view_2=CloseCacheView(view_2);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]444 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]445 { /* an exception was thrown */ }
446</pre>
447</div>
448
449<h3>Magick Persistent Cache Format</h3>
450<div class="doc-section">
451
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]452<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]453<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]454</div>
455
456<h3>Best Practices</h3>
457<div class="doc-section">
458
459<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>
460
461<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>
462
463<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>
464
465<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>
466
467<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>
468
469<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>
470
471<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>
472
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]473<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]474
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]475<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]476
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]477<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]478
479<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>
480
481<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>
482<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>
483</div>
484
485</div>
486
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]487<h2><a id="stream"></a>Streaming Pixels</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]488<div class="doc-section">
489
490<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>
491
492<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>
493
494<pre class="code">
495static size_t StreamHandler(const Image *image,const void *pixels,
496 const size_t columns)
497{
498 /* process pixels here */
499 return(columns);
500}
501
502...
503/* invoke the pixel stream here */
504image=ReadStream(image_info,&amp;StreamHandler,exception);
505</pre>
506
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]507<p>We also provide a lightweight tool, <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 href="../www/stream.html">stream</a> desirable when working with large images or when you require raw pixel components.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]508
509</div>
510
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]511<h2><a id="properties"></a>Image Properties and Profiles</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]512<div class="doc-section">
513
514<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>
515
516<pre class="code">
517 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
518</pre>
519
520<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>
521
522<pre class="code">
523 const char
524 *comment;
525
526 (void) SetImageProperty(image,"comment","This space for rent");
527 comment=GetImageProperty(image,"comment");
528 if (comment == (const char *) NULL)
529 (void) printf("Image comment: %s\n",comment);
530</pre>
531
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]532<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]533
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]534<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>
535
536<pre class="code">
537 StringInfo
538 *profile;
539
540 profile=AcquireStringInfo(length);
541 SetStringInfoDatum(profile,my_exif_profile);
542 (void) SetImageProfile(image,"EXIF",profile);
543 DestroyStringInfo(profile);
544 profile=GetImageProfile(image,"EXIF");
545 if (profile != (StringInfo *) NULL)
546 (void) PrintStringInfo(stdout,"EXIF",profile);
547</pre>
548
549</div>
550
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]551<h2><a id="tera-pixel"></a>Large Image Support</h2>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]552<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]553<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]554
555<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]556<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]557
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]558<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]559<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>
560
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]561<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]562<p>Here we force all image pixels to disk:</p>
563
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]564<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]565<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]566
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]567<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]568
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]569<h2><a id="threads"></a>Threads of Execution</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]570<div class="doc-section">
571
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]572<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]573
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]574<p>Here is an MagickCore code snippet that takes 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]575
576<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]577{
578 CacheView
579 *image_view;
580
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]581 MagickBooleanType
582 status;
583
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]584 ssize_t
585 y;
586
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]587 status=MagickTrue;
588 image_view=AcquireCacheView(image);
589 #pragma omp parallel for schedule(dynamic,4) shared(status)
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]590 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]591 {
592 register IndexPacket
593 *indexes;
594
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]595 register PixelPacket
596 *q;
597
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]598 register ssize_t
599 x;
600
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]601 if (status == MagickFalse)
602 continue;
603 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
604 if (q == (PixelPacket *) NULL)
605 {
606 status=MagickFalse;
607 continue;
608 }
609 indexes=GetCacheViewAuthenticIndexQueue(image_view);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]610 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]611 {
612 q-&gt;red= ...
613 q-&gt;green= ...
614 q-&gt;blue= ...
615 q-&gt;opacity= ...
616 if (indexes != (IndexPacket *) NULL)
617 indexes[x]= ...
618 q++;
619 }
620 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
621 status=MagickFalse;
622 }
623 image_view=DestroyCacheView(image_view);
624 if (status == MagickFalse)
625 perror("something went wrong");
626}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]627</div>
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]628<p>This code snippet converts an uncompressed Windows bitmap to a Magick++ image:</p>
629<div class="viewport">
630#include "Magick++.h"
631#include &lt;assert.h&gt;
632#include "omp.h"
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]633
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]634void ConvertBMPToImage(const BITMAPINFOHEADER *bmp_info,
635 const unsigned char *restrict pixels,Magick::Image *image)
636{
637 /*
638 Prepare the image so that we can modify the pixels directly.
639 */
640 assert(bmp_info->biCompression == BI_RGB);
641 assert(bmp_info->biWidth == image->columns());
642 assert(abs(bmp_info->biHeight) == image->rows());
643 image->modifyImage();
644 if (bmp_info->biBitCount == 24)
645 image->type(MagickCore::TrueColorType);
646 else
647 image->type(MagickCore::TrueColorMatteType);
648 register unsigned int bytes_per_row=bmp_info->biWidth*bmp_info->biBitCount/8;
649 if (bytes_per_row % 4 != 0) {
650 bytes_per_row=bytes_per_row+(4-bytes_per_row % 4); // divisible by 4.
651 }
652 /*
653 Copy all pixel data, row by row.
654 */
655 #pragma omp parallel for
656 for (int y=0; y < int(image->rows()); y++)
657 {
658 int row=(bmp_info->biHeight > 0) ? (image->rows()-y-1) : y;
659 register const unsigned char *restrict p=pixels+row*bytes_per_row;
660 register MagickCore::PixelPacket *restrict q=
661 image->setPixels(0,y,image->columns(),1);
662 for (int x=0; x < int(image->columns()); x++)
663 {
664 q->blue=p[0];
665 q->green=p[1];
666 q->red=p[2];
667 if (bmp_info->biBitCount == 32) {
668 q->opacity=p[3];
669 }
670 q++;
671 p+=bmp_info->biBitCount/8;
672 }
673 image->syncPixels(); // sync pixels to pixel cache.
674 }
675 return;
676}
677</div>
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]678
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]679<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>
680
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]681<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]682
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]683<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]684
685<pre class="text">
686 &lt;policy domain="resource" name="thread" value="2"/>
687</pre>
688
689<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>
690
691<pre class="text">
692 export MAGICK_THREAD_LIMIT=12
693</pre>
694
695<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>
696
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]697</div>
698
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]699<h2><a id="distributed"></a>Heterogeneous Distributed Processing</h2>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]700<div class="doc-section">
701<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>
702
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]703<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]704
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]705<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
706<p>If so, run this command to realize a significant speed-up for image convolution:</p>
707
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]708<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]709<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
710
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]711<p>Here is an example OpenCL kernel that convolves an image:</p>
712
713<div class="viewport">
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]714static inline long ClampToCanvas(const long offset,const ulong range)
715{
716 if (offset &lt; 0L)
717 return(0L);
718 if (offset >= range)
719 return((long) (range-1L));
720 return(offset);
721}
722
723static inline CLQuantum ClampToQuantum(const double value)
724{
725 if (value &lt; 0.0)
726 return((CLQuantum) 0);
727 if (value >= (double) QuantumRange)
728 return((CLQuantum) QuantumRange);
729 return((CLQuantum) (value+0.5));
730}
731
732__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
733 const ulong width,const ulong height,__global CLPixelType *destination)
734{
735 const ulong columns = get_global_size(0);
736 const ulong rows = get_global_size(1);
737
738 const long x = get_global_id(0);
739 const long y = get_global_id(1);
740
741 const double scale = (1.0/QuantumRange);
742 const long mid_width = (width-1)/2;
743 const long mid_height = (height-1)/2;
744 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
745 double gamma = 0.0;
746 register ulong i = 0;
747
748 for (long v=(-mid_height); v &lt;= mid_height; v++)
749 {
750 for (long u=(-mid_width); u &lt;= mid_width; u++)
751 {
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]752 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,
753 columns);
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]754 const double alpha=scale*(QuantumRange-source[index].w);
755 sum.x+=alpha*filter[i]*source[index].x;
756 sum.y+=alpha*filter[i]*source[index].y;
757 sum.z+=alpha*filter[i]*source[index].z;
758 sum.w+=filter[i]*source[index].w;
759 gamma+=alpha*filter[i];
760 i++;
761 }
762 }
763
764 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
765 const ulong index=y*columns+x;
766 destination[index].x=ClampToQuantum(gamma*sum.x);
767 destination[index].y=ClampToQuantum(gamma*sum.y);
768 destination[index].z=ClampToQuantum(gamma*sum.z);
769 destination[index].w=ClampToQuantum(sum.w);
770};
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]771</div>
772
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]773<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]774
775</div>
776
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]777<h2><a id="coders"></a>Custom Image Coders</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]778<div class="doc-section">
779
780<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>
781
782<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>
783
784<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]785/*
786 Include declarations.
787*/
788#include "magick/studio.h"
789#include "magick/blob.h"
790#include "magick/blob-private.h"
791#include "magick/colorspace.h"
792#include "magick/exception.h"
793#include "magick/exception-private.h"
794#include "magick/image.h"
795#include "magick/image-private.h"
796#include "magick/list.h"
797#include "magick/magick.h"
798#include "magick/memory_.h"
799#include "magick/monitor.h"
800#include "magick/monitor-private.h"
801#include "magick/quantum-private.h"
802#include "magick/static.h"
803#include "magick/string_.h"
804#include "magick/module.h"
805
806/*
807 Forward declarations.
808*/
809static MagickBooleanType
810 WriteMGKImage(const ImageInfo *,Image *);
811
812/*
813%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
814% %
815% %
816% %
817% I s M G K %
818% %
819% %
820% %
821%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
822%
823% IsMGK() returns MagickTrue if the image format type, identified by the
824% magick string, is MGK.
825%
826% The format of the IsMGK method is:
827%
828% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
829%
830% A description of each parameter follows:
831%
832% o magick: This string is generally the first few bytes of an image file
833% or blob.
834%
835% o length: Specifies the length of the magick string.
836%
837*/
838static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
839{
840 if (length &lt; 7)
841 return(MagickFalse);
842 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
843 return(MagickTrue);
844 return(MagickFalse);
845}
846
847/*
848%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
849% %
850% %
851% %
852% R e a d M G K I m a g e %
853% %
854% %
855% %
856%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
857%
858% ReadMGKImage() reads a MGK image file and returns it. It allocates
859% the memory necessary for the new Image structure and returns a pointer to
860% the new image.
861%
862% The format of the ReadMGKImage method is:
863%
864% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
865%
866% A description of each parameter follows:
867%
868% o image_info: the image info.
869%
870% o exception: return any errors or warnings in this structure.
871%
872*/
873static Image *ReadMGKImage(const ImageInfo *image_info,
874 ExceptionInfo *exception)
875{
876 char
877 buffer[MaxTextExtent];
878
879 Image
880 *image;
881
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]882 MagickBooleanType
883 status;
884
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]885 register PixelPacket
886 *q;
887
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]888 register size_t
889 x;
890
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]891 register unsigned char
892 *p;
893
894 ssize_t
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]895 count,
896 y;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]897
898 unsigned char
899 *pixels;
900
901 unsigned long
902 columns,
903 rows;
904
905 /*
906 Open image file.
907 */
908 assert(image_info != (const ImageInfo *) NULL);
909 assert(image_info-&gt;signature == MagickSignature);
910 if (image_info-&gt;debug != MagickFalse)
911 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
912 assert(exception != (ExceptionInfo *) NULL);
913 assert(exception-&gt;signature == MagickSignature);
914 image=AcquireImage(image_info);
915 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
916 if (status == MagickFalse)
917 {
918 image=DestroyImageList(image);
919 return((Image *) NULL);
920 }
921 /*
922 Read MGK image.
923 */
924 (void) ReadBlobString(image,buffer); /* read magic number */
925 if (IsMGK(buffer,7) == MagickFalse)
926 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
927 (void) ReadBlobString(image,buffer);
928 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
929 if (count &lt;= 0)
930 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
931 do
932 {
933 /*
934 Initialize image structure.
935 */
936 image-&gt;columns=columns;
937 image-&gt;rows=rows;
938 image-&gt;depth=8;
939 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
940 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
941 break;
942 /*
943 Convert MGK raster image to pixel packets.
944 */
945 if (SetImageExtent(image,0,0) == MagickFalse)
946 {
947 InheritException(exception,&amp;image-&gt;exception);
948 return(DestroyImageList(image));
949 }
950 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
951 if (pixels == (unsigned char *) NULL)
952 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]953 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]954 {
955 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
956 if (count != (ssize_t) (3*image-&gt;columns))
957 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
958 p=pixels;
959 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
960 if (q == (PixelPacket *) NULL)
961 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]962 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]963 {
964 q-&gt;red=ScaleCharToQuantum(*p++);
965 q-&gt;green=ScaleCharToQuantum(*p++);
966 q-&gt;blue=ScaleCharToQuantum(*p++);
967 q++;
968 }
969 if (SyncAuthenticPixels(image,exception) == MagickFalse)
970 break;
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]971 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]972 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
973 break;
974 }
975 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
976 if (EOFBlob(image) != MagickFalse)
977 {
978 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
979 break;
980 }
981 /*
982 Proceed to next image.
983 */
984 if (image_info-&gt;number_scenes != 0)
985 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
986 break;
987 *buffer='\0';
988 (void) ReadBlobString(image,buffer);
989 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
990 if (count != 0)
991 {
992 /*
993 Allocate next image structure.
994 */
995 AcquireNextImage(image_info,image);
996 if (GetNextImageInList(image) == (Image *) NULL)
997 {
998 image=DestroyImageList(image);
999 return((Image *) NULL);
1000 }
1001 image=SyncNextImageInList(image);
1002 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
1003 if (status == MagickFalse)
1004 break;
1005 }
1006 } while (count != 0);
1007 (void) CloseBlob(image);
1008 return(GetFirstImageInList(image));
1009}
1010
1011/*
1012%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1013% %
1014% %
1015% %
1016% R e g i s t e r M G K I m a g e %
1017% %
1018% %
1019% %
1020%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1021%
1022% RegisterMGKImage() adds attributes for the MGK image format to
1023% the list of supported formats. The attributes include the image format
1024% tag, a method to read and/or write the format, whether the format
1025% supports the saving of more than one frame to the same file or blob,
1026% whether the format supports native in-memory I/O, and a brief
1027% description of the format.
1028%
1029% The format of the RegisterMGKImage method is:
1030%
1031% unsigned long RegisterMGKImage(void)
1032%
1033*/
1034ModuleExport unsigned long RegisterMGKImage(void)
1035{
1036 MagickInfo
1037 *entry;
1038
1039 entry=SetMagickInfo("MGK");
1040 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
1041 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
1042 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
1043 entry-&gt;description=ConstantString("MGK");
1044 entry-&gt;module=ConstantString("MGK");
1045 (void) RegisterMagickInfo(entry);
1046 return(MagickImageCoderSignature);
1047}
1048
1049/*
1050%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1051% %
1052% %
1053% %
1054% U n r e g i s t e r M G K I m a g e %
1055% %
1056% %
1057% %
1058%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1059%
1060% UnregisterMGKImage() removes format registrations made by the
1061% MGK module from the list of supported formats.
1062%
1063% The format of the UnregisterMGKImage method is:
1064%
1065% UnregisterMGKImage(void)
1066%
1067*/
1068ModuleExport void UnregisterMGKImage(void)
1069{
1070 (void) UnregisterMagickInfo("MGK");
1071}
1072
1073/*
1074%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1075% %
1076% %
1077% %
1078% W r i t e M G K I m a g e %
1079% %
1080% %
1081% %
1082%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1083%
1084% WriteMGKImage() writes an image to a file in red, green, and blue
1085% MGK rasterfile format.
1086%
1087% The format of the WriteMGKImage method is:
1088%
1089% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1090%
1091% A description of each parameter follows.
1092%
1093% o image_info: the image info.
1094%
1095% o image: The image.
1096%
1097*/
1098static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1099{
1100 char
1101 buffer[MaxTextExtent];
1102
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1103 MagickBooleanType
1104 status;
1105
1106 MagickOffsetType
1107 scene;
1108
1109 register const PixelPacket
1110 *p;
1111
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1112 register ssize_t
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1113 x;
1114
1115 register unsigned char
1116 *q;
1117
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1118 ssize_t
1119 y;
1120
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1121 unsigned char
1122 *pixels;
1123
1124 /*
1125 Open output image file.
1126 */
1127 assert(image_info != (const ImageInfo *) NULL);
1128 assert(image_info-&gt;signature == MagickSignature);
1129 assert(image != (Image *) NULL);
1130 assert(image-&gt;signature == MagickSignature);
1131 if (image-&gt;debug != MagickFalse)
1132 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1133 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1134 if (status == MagickFalse)
1135 return(status);
1136 scene=0;
1137 do
1138 {
1139 /*
1140 Allocate memory for pixels.
1141 */
1142 if (image-&gt;colorspace != RGBColorspace)
1143 (void) SetImageColorspace(image,RGBColorspace);
1144 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1145 3UL*sizeof(*pixels));
1146 if (pixels == (unsigned char *) NULL)
1147 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1148 /*
1149 Initialize raster file header.
1150 */
1151 (void) WriteBlobString(image,"id=mgk\n");
1152 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1153 image-&gt;columns,image-&gt;rows);
1154 (void) WriteBlobString(image,buffer);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1155 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1156 {
1157 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1158 if (p == (const PixelPacket *) NULL)
1159 break;
1160 q=pixels;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1161 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1162 {
1163 *q++=ScaleQuantumToChar(p-&gt;red);
1164 *q++=ScaleQuantumToChar(p-&gt;green);
1165 *q++=ScaleQuantumToChar(p-&gt;blue);
1166 p++;
1167 }
1168 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1169 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1170 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1171 break;
1172 }
1173 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1174 if (GetNextImageInList(image) == (Image *) NULL)
1175 break;
1176 image=SyncNextImageInList(image);
1177 status=SetImageProgress(image,SaveImagesTag,scene,
1178 GetImageListLength(image));
1179 if (status == MagickFalse)
1180 break;
1181 scene++;
1182 } while (image_info-&gt;adjoin != MagickFalse);
1183 (void) CloseBlob(image);
1184 return(MagickTrue);
1185}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1186</div>
1187
1188<p>To invoke the custom coder from the command line, use these commands:</p>
1189
1190<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>
1191<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>
1192
1193</div>
1194
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1195<h2><a id="filters"></a>Custom Image Filters</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1196<div class="doc-section">
1197
1198<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>
1199
1200<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>
1201
1202<div class="viewport">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1203#include &lt;stdio.h&gt;
1204#include &lt;stdlib.h&gt;
1205#include &lt;string.h&gt;
1206#include &lt;time.h&gt;
1207#include &lt;assert.h&gt;
1208#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1209#include "magick/MagickCore.h"
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1210
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1211/*
1212%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1213% %
1214% %
1215% %
1216% a n a l y z e I m a g e %
1217% %
1218% %
1219% %
1220%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1221%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1222% analyzeImage() computes the brightness and saturation mean, standard
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]1223% deviation, kurtosis and skewness and stores these values as attributes
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1224% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1225%
1226% The format of the analyzeImage method is:
1227%
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame^]1228% size_t analyzeImage(Image *images,const int argc,char **argv,
1229% ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1230%
1231% A description of each parameter follows:
1232%
1233% o image: the address of a structure of type Image.
1234%
1235% o argc: Specifies a pointer to an integer describing the number of
1236% elements in the argument vector.
1237%
1238% o argv: Specifies a pointer to a text array containing the command line
1239% arguments.
1240%
1241% o exception: return any errors or warnings in this structure.
1242%
1243*/
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame^]1244ModuleExport size_t analyzeImage(Image **images,const int argc,const char **argv,
1245 ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1246{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1247 char
1248 text[MaxTextExtent];
1249
1250 double
1251 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1252 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1253 brightness_mean,
1254 brightness_standard_deviation,
1255 brightness_kurtosis,
1256 brightness_skewness,
1257 brightness_sum_x,
1258 brightness_sum_x2,
1259 brightness_sum_x3,
1260 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1261 hue,
1262 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1263 saturation_mean,
1264 saturation_standard_deviation,
1265 saturation_kurtosis,
1266 saturation_skewness,
1267 saturation_sum_x,
1268 saturation_sum_x2,
1269 saturation_sum_x3,
1270 saturation_sum_x4;
1271
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1272 Image
1273 *image;
1274
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1275 assert(images != (Image **) NULL);
1276 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1277 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1278 (void) argc;
1279 (void) argv;
1280 image=(*images);
1281 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1282 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1283 CacheView
1284 *image_view;
1285
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1286 MagickBooleanType
1287 status;
1288
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1289 ssize_t
1290 y;
1291
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1292 brightness_sum_x=0.0;
1293 brightness_sum_x2=0.0;
1294 brightness_sum_x3=0.0;
1295 brightness_sum_x4=0.0;
1296 brightness_mean=0.0;
1297 brightness_standard_deviation=0.0;
1298 brightness_kurtosis=0.0;
1299 brightness_skewness=0.0;
1300 saturation_sum_x=0.0;
1301 saturation_sum_x2=0.0;
1302 saturation_sum_x3=0.0;
1303 saturation_sum_x4=0.0;
1304 saturation_mean=0.0;
1305 saturation_standard_deviation=0.0;
1306 saturation_kurtosis=0.0;
1307 saturation_skewness=0.0;
1308 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1309 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1310 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1311#if defined(MAGICKCORE_OPENMP_SUPPORT)
1312 #pragma omp parallel for schedule(dynamic,4) shared(status)
1313#endif
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1314 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1315 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1316 register const PixelPacket
1317 *p;
1318
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1319 register ssize_t
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1320 x;
1321
1322 if (status == MagickFalse)
1323 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1324 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1325 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1326 {
1327 status=MagickFalse;
1328 continue;
1329 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1330 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1331 {
1332 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1333 brightness*=QuantumRange;
1334 brightness_sum_x+=brightness;
1335 brightness_sum_x2+=brightness*brightness;
1336 brightness_sum_x3+=brightness*brightness*brightness;
1337 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1338 saturation*=QuantumRange;
1339 saturation_sum_x+=saturation;
1340 saturation_sum_x2+=saturation*saturation;
1341 saturation_sum_x3+=saturation*saturation*saturation;
1342 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1343 area++;
1344 p++;
1345 }
1346 }
1347 image_view=DestroyCacheView(image_view);
1348 if (area &lt;= 0.0)
1349 break;
1350 brightness_mean=brightness_sum_x/area;
1351 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1352 (void) SetImageProperty(image,"filter:brightness:mean",text);
1353 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1354 area*brightness_sum_x/area));
1355 (void) FormatMagickString(text,MaxTextExtent,"%g",
1356 brightness_standard_deviation);
1357 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1358 if (brightness_standard_deviation != 0)
1359 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1360 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1361 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1362 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1363 brightness_standard_deviation*brightness_standard_deviation*
1364 brightness_standard_deviation)-3.0;
1365 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1366 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1367 if (brightness_standard_deviation != 0)
1368 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1369 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1370 brightness_mean)/(brightness_standard_deviation*
1371 brightness_standard_deviation*brightness_standard_deviation);
1372 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1373 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1374 saturation_mean=saturation_sum_x/area;
1375 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1376 (void) SetImageProperty(image,"filter:saturation:mean",text);
1377 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1378 area*saturation_sum_x/area));
1379 (void) FormatMagickString(text,MaxTextExtent,"%g",
1380 saturation_standard_deviation);
1381 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1382 if (saturation_standard_deviation != 0)
1383 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1384 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1385 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1386 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1387 saturation_standard_deviation*saturation_standard_deviation*
1388 saturation_standard_deviation)-3.0;
1389 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1390 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1391 if (saturation_standard_deviation != 0)
1392 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1393 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1394 saturation_mean)/(saturation_standard_deviation*
1395 saturation_standard_deviation*saturation_standard_deviation);
1396 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1397 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1398 }
1399 return(MagickImageFilterSignature);
1400}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1401</div>
1402
1403<p>To invoke the custom filter from the command line, use this command:</p>
1404
1405<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/>
1406 Format: LOGO (ImageMagick Logo) <br/>
1407 Class: PseudoClass <br/>
1408 Geometry: 640x480 <br/>
1409 ... <br/>
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame^]1410 filter:brightness:kurtosis: 8.17947 <br/>
1411 filter:brightness:mean: 60632.1 <br/>
1412 filter:brightness:skewness: -2.97118 <br/>
1413 filter:brightness:standard-deviation: 13742.1 <br/>
1414 filter:saturation:kurtosis: 4.33554 <br/>
1415 filter:saturation:mean: 5951.55 <br/>
1416 filter:saturation:skewness: 2.42848 <br/>
1417 filter:saturation:standard-deviation: 15575.9</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1418
1419<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>
1420
1421</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1422
1423</div>
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