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cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]7 <title>ImageMagick: Architecture</title>
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175
176<div class="main">
177
178
179
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]180<h1>The <em>Magick</em> Behind ImageMagick</h1>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]181<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]182
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]183
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]184<div class="doc-section">
185<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>
186</div>
187
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]188<h2><a id="overview"></a>Architecture Overview</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]189<div class="doc-section">
190
191<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>
192
193<ul>
194 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
195 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
196 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
197 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
198 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
199 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
200</ul>
201
202<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>
203
204<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
205
206<ul>
207 <li>one pixel a time (e.g. pixel at location 10,3)</li>
208 <li>a single scanline (e.g. all pixels from row 4)</li>
209 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
210 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
211 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
212 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
213 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
214 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
215 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
216 <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>
217 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]218 <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]219</ul>
220
221<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>
222
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]223<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]224
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]225<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]226
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]227<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]228
229</div>
230
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]231<h2><a id="cache"></a>The Pixel Cache</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]232<div class="doc-section">
233
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]234<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]235
236<h3>Create the Pixel Cache</h3>
237<div class="doc-section">
238
239<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>
240
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]241<dl>
242<dt>Create an image canvas initialized to the background color:</dt>
243<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]244 image=AllocateImage(image_info);
245 if (SetImageExtent(image,640,480) == MagickFalse)
246 { /* an exception was thrown */ }
247 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
248 SetImageBackgroundColor(image);
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]249</p></dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]250
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]251<dt>Create an image from a JPEG image on disk:</dt>
252<dd><p class="code">
253 (void) strcpy(image_info-&gt;filename,"image.jpg"):
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]254 image=ReadImage(image_info,exception);
255 if (image == (Image *) NULL)
256 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]257</p></dd>
258<dt>Create an image from a memory based image:</dt>
259<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]260 image=BlobToImage(blob_info,blob,extent,exception);
261 if (image == (Image *) NULL)
262 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]263</p></dd>
264</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]265
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]266<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]267
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]268<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]269
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]270<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.7-0 2010-01-01 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]271<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]272</div>
273
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]274<h3><a id="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]275<div class="doc-section">
276
277<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]278<dl>
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]279 <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]280 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
281 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
282 <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]283</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]284
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]285<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]286
287<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]288 const PixelPacket
289 *p;
290
291 PixelPacket
292 *q;
293
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]294 ssize_t
295 x,
296 y;
297
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]298 destination=CloneImage(source,source->columns,source->rows,MagickTrue,
299 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]300 if (destination == (Image *) NULL)
301 { /* an exception was thrown */ }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]302 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]303 {
304 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
305 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
306 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
307 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]308 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]309 {
310 q-&gt;red=90*p-&gt;red/100;
311 q-&gt;green=90*p-&gt;green/100;
312 q-&gt;blue=90*p-&gt;blue/100;
313 q-&gt;opacity=90*p-&gt;opacity/100;
314 p++;
315 q++;
316 }
317 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
318 break;
319 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]320 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]321 { /* an exception was thrown */ }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]322</div>
323
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]324<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]325
326<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>
327
328<pre class="code">
329 const IndexPacket
330 *indexes;
331
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]332 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]333 {
334 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
335 if (p == (const PixelPacket *) NULL)
336 break;
337 indexes=GetVirtualIndexes(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]338 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]339 (void) printf("%d\n",indexes[x];
340 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]341 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]342 /* an exception was thrown */
343</pre>
344
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]345<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]346
347<pre class="code">
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]348 p=GetVirtualPixels(source,-3,-3,source-&gt;columns+3,6,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]349</pre>
350
351<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
352</div>
353
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]354<h3><a id="virtual-pixels"></a>Virtual Pixels</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]355<div class="doc-section">
356
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]357<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]358 <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>
359
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]360<pre class="text" style="font-size: 90%;">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]361 background: the area surrounding the image is the background color
362 black: the area surrounding the image is black
363 checker-tile: alternate squares with image and background color
364 dither: non-random 32x32 dithered pattern
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]365 edge: extend the edge pixel toward infinity (default)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]366 gray: the area surrounding the image is gray
367 horizontal-tile: horizontally tile the image, background color above/below
368 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
369 mirror: mirror tile the image
370 random: choose a random pixel from the image
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]371 tile: tile the image
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]372 transparent: the area surrounding the image is transparent blackness
373 vertical-tile: vertically tile the image, sides are background color
374 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
375 white: the area surrounding the image is white
376</pre>
377
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]378</div>
379
380<h3>Cache Storage and Resource Requirements</h3>
381<div class="doc-section">
382
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]383<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]384
385<dl class="doc">
386 <dt class="doc">files</dt>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]387 <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]388 <dt class="doc">area</dt>
389 <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>
390 <dt class="doc">memory</dt>
391 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
392 <dt class="doc">map</dt>
393 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
394 <dt class="doc">disk</dt>
395 <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]396 <dt class="doc">thread</dt>
397 <dd>maximum number of threads that are permitted to run in parallel.</dd>
398 <dt class="doc">time</dt>
399 <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]400</dl>
401
402<p>To determine the current setting of these limits, use this command:</p>
403
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]404<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span></p><pre class="text">
405File Area Memory Map Disk Thread Time
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]406-------------------------------------------------------------------------------
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]407 768 1.0386GB 3.8692GiB 7.7384GiB unlimited 4 unlimited
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]408</pre>
409
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]410<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]411
412<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>
413</div>
414
415<h3>Cache Views</h3>
416<div class="doc-section">
417
418<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>
419
420<pre class="code">
421 CacheView
422 *view_1,
423 *view_2;
424
425 view_1=OpenCacheView(source);
426 view_2=OpenCacheView(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]427 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]428 {
429 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]430 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,
431 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]432 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
433 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]434 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]435 {
436 /* do something with u &amp; v here */
437 }
438 }
439 view_1=CloseCacheView(view_1);
440 view_2=CloseCacheView(view_2);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]441 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]442 { /* an exception was thrown */ }
443</pre>
444</div>
445
446<h3>Magick Persistent Cache Format</h3>
447<div class="doc-section">
448
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]449<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]450<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]451</div>
452
453<h3>Best Practices</h3>
454<div class="doc-section">
455
456<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>
457
458<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>
459
460<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>
461
462<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>
463
464<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>
465
466<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>
467
468<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>
469
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]470<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]471
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]472<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]473
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]474<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]475
476<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>
477
478<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>
479<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>
480</div>
481
482</div>
483
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]484<h2><a id="stream"></a>Streaming Pixels</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]485<div class="doc-section">
486
487<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>
488
489<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>
490
491<pre class="code">
492static size_t StreamHandler(const Image *image,const void *pixels,
493 const size_t columns)
494{
495 /* process pixels here */
496 return(columns);
497}
498
499...
500/* invoke the pixel stream here */
501image=ReadStream(image_info,&amp;StreamHandler,exception);
502</pre>
503
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]504<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]505
506</div>
507
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]508<h2><a id="properties"></a>Image Properties and Profiles</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]509<div class="doc-section">
510
511<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>
512
513<pre class="code">
514 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
515</pre>
516
517<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>
518
519<pre class="code">
520 const char
521 *comment;
522
523 (void) SetImageProperty(image,"comment","This space for rent");
524 comment=GetImageProperty(image,"comment");
525 if (comment == (const char *) NULL)
526 (void) printf("Image comment: %s\n",comment);
527</pre>
528
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]529<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]530
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]531<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>
532
533<pre class="code">
534 StringInfo
535 *profile;
536
537 profile=AcquireStringInfo(length);
538 SetStringInfoDatum(profile,my_exif_profile);
539 (void) SetImageProfile(image,"EXIF",profile);
540 DestroyStringInfo(profile);
541 profile=GetImageProfile(image,"EXIF");
542 if (profile != (StringInfo *) NULL)
543 (void) PrintStringInfo(stdout,"EXIF",profile);
544</pre>
545
546</div>
547
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]548<h2><a id="tera-pixel"></a>Large Image Support</h2>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]549<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]550<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]551
552<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]553<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]554
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]555<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]556<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>
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 -limit memory 16mb \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]559<p>Here we force all image pixels to disk:</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 area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
cristybac7a162010-06-15 19:57:29 +0000[diff] [blame]562<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]563
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]564<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]565
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]566<h2><a id="threads"></a>Threads of Execution</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]567<div class="doc-section">
568
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]569<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]570
cristy52923442011-01-15 22:54:31 +0000[diff] [blame^]571<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]572
573<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]574{
575 CacheView
576 *image_view;
577
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]578 MagickBooleanType
579 status;
580
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]581 ssize_t
582 y;
583
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]584 status=MagickTrue;
585 image_view=AcquireCacheView(image);
586 #pragma omp parallel for schedule(dynamic,4) shared(status)
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]587 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]588 {
589 register IndexPacket
590 *indexes;
591
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]592 register PixelPacket
593 *q;
594
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]595 register ssize_t
596 x;
597
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]598 if (status == MagickFalse)
599 continue;
600 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
601 if (q == (PixelPacket *) NULL)
602 {
603 status=MagickFalse;
604 continue;
605 }
606 indexes=GetCacheViewAuthenticIndexQueue(image_view);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]607 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]608 {
609 q-&gt;red= ...
610 q-&gt;green= ...
611 q-&gt;blue= ...
612 q-&gt;opacity= ...
613 if (indexes != (IndexPacket *) NULL)
614 indexes[x]= ...
615 q++;
616 }
617 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
618 status=MagickFalse;
619 }
620 image_view=DestroyCacheView(image_view);
621 if (status == MagickFalse)
622 perror("something went wrong");
623}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]624</div>
cristy52923442011-01-15 22:54:31 +0000[diff] [blame^]625<p>This code snippet converts an uncompressed Windows bitmap to a Magick++ image:</p>
626<div class="viewport">
627#include "Magick++.h"
628#include &lt;assert.h&gt;
629#include "omp.h"
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]630
cristy52923442011-01-15 22:54:31 +0000[diff] [blame^]631void ConvertBMPToImage(const BITMAPINFOHEADER *bmp_info,
632 const unsigned char *restrict pixels,Magick::Image *image)
633{
634 /*
635 Prepare the image so that we can modify the pixels directly.
636 */
637 assert(bmp_info->biCompression == BI_RGB);
638 assert(bmp_info->biWidth == image->columns());
639 assert(abs(bmp_info->biHeight) == image->rows());
640 image->modifyImage();
641 if (bmp_info->biBitCount == 24)
642 image->type(MagickCore::TrueColorType);
643 else
644 image->type(MagickCore::TrueColorMatteType);
645 register unsigned int bytes_per_row=bmp_info->biWidth*bmp_info->biBitCount/8;
646 if (bytes_per_row % 4 != 0) {
647 bytes_per_row=bytes_per_row+(4-bytes_per_row % 4); // divisible by 4.
648 }
649 /*
650 Copy all pixel data, row by row.
651 */
652 #pragma omp parallel for
653 for (int y=0; y < int(image->rows()); y++)
654 {
655 int row=(bmp_info->biHeight > 0) ? (image->rows()-y-1) : y;
656 register const unsigned char *restrict p=pixels+row*bytes_per_row;
657 register MagickCore::PixelPacket *restrict q=
658 image->setPixels(0,y,image->columns(),1);
659 for (int x=0; x < int(image->columns()); x++)
660 {
661 q->blue=p[0];
662 q->green=p[1];
663 q->red=p[2];
664 if (bmp_info->biBitCount == 32) {
665 q->opacity=p[3];
666 }
667 q++;
668 p+=bmp_info->biBitCount/8;
669 }
670 image->syncPixels(); // sync pixels to pixel cache.
671 }
672 return;
673}
674</div>
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]675
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]676<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>
677
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]678<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]679
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]680<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]681
682<pre class="text">
683 &lt;policy domain="resource" name="thread" value="2"/>
684</pre>
685
686<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>
687
688<pre class="text">
689 export MAGICK_THREAD_LIMIT=12
690</pre>
691
692<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>
693
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]694</div>
695
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]696<h2><a id="distributed"></a>Heterogeneous Distributed Processing</h2>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]697<div class="doc-section">
698<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>
699
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]700<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]701
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]702<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
703<p>If so, run this command to realize a significant speed-up for image convolution:</p>
704
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]705<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]706<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
707
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]708<p>Here is an example OpenCL kernel that convolves an image:</p>
709
710<div class="viewport">
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]711static inline long ClampToCanvas(const long offset,const ulong range)
712{
713 if (offset &lt; 0L)
714 return(0L);
715 if (offset >= range)
716 return((long) (range-1L));
717 return(offset);
718}
719
720static inline CLQuantum ClampToQuantum(const double value)
721{
722 if (value &lt; 0.0)
723 return((CLQuantum) 0);
724 if (value >= (double) QuantumRange)
725 return((CLQuantum) QuantumRange);
726 return((CLQuantum) (value+0.5));
727}
728
729__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
730 const ulong width,const ulong height,__global CLPixelType *destination)
731{
732 const ulong columns = get_global_size(0);
733 const ulong rows = get_global_size(1);
734
735 const long x = get_global_id(0);
736 const long y = get_global_id(1);
737
738 const double scale = (1.0/QuantumRange);
739 const long mid_width = (width-1)/2;
740 const long mid_height = (height-1)/2;
741 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
742 double gamma = 0.0;
743 register ulong i = 0;
744
745 for (long v=(-mid_height); v &lt;= mid_height; v++)
746 {
747 for (long u=(-mid_width); u &lt;= mid_width; u++)
748 {
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]749 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,
750 columns);
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]751 const double alpha=scale*(QuantumRange-source[index].w);
752 sum.x+=alpha*filter[i]*source[index].x;
753 sum.y+=alpha*filter[i]*source[index].y;
754 sum.z+=alpha*filter[i]*source[index].z;
755 sum.w+=filter[i]*source[index].w;
756 gamma+=alpha*filter[i];
757 i++;
758 }
759 }
760
761 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
762 const ulong index=y*columns+x;
763 destination[index].x=ClampToQuantum(gamma*sum.x);
764 destination[index].y=ClampToQuantum(gamma*sum.y);
765 destination[index].z=ClampToQuantum(gamma*sum.z);
766 destination[index].w=ClampToQuantum(sum.w);
767};
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]768</div>
769
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]770<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]771
772</div>
773
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]774<h2><a id="coders"></a>Custom Image Coders</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]775<div class="doc-section">
776
777<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>
778
779<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>
780
781<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]782/*
783 Include declarations.
784*/
785#include "magick/studio.h"
786#include "magick/blob.h"
787#include "magick/blob-private.h"
788#include "magick/colorspace.h"
789#include "magick/exception.h"
790#include "magick/exception-private.h"
791#include "magick/image.h"
792#include "magick/image-private.h"
793#include "magick/list.h"
794#include "magick/magick.h"
795#include "magick/memory_.h"
796#include "magick/monitor.h"
797#include "magick/monitor-private.h"
798#include "magick/quantum-private.h"
799#include "magick/static.h"
800#include "magick/string_.h"
801#include "magick/module.h"
802
803/*
804 Forward declarations.
805*/
806static MagickBooleanType
807 WriteMGKImage(const ImageInfo *,Image *);
808
809/*
810%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
811% %
812% %
813% %
814% I s M G K %
815% %
816% %
817% %
818%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
819%
820% IsMGK() returns MagickTrue if the image format type, identified by the
821% magick string, is MGK.
822%
823% The format of the IsMGK method is:
824%
825% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
826%
827% A description of each parameter follows:
828%
829% o magick: This string is generally the first few bytes of an image file
830% or blob.
831%
832% o length: Specifies the length of the magick string.
833%
834*/
835static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
836{
837 if (length &lt; 7)
838 return(MagickFalse);
839 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
840 return(MagickTrue);
841 return(MagickFalse);
842}
843
844/*
845%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
846% %
847% %
848% %
849% R e a d M G K I m a g e %
850% %
851% %
852% %
853%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
854%
855% ReadMGKImage() reads a MGK image file and returns it. It allocates
856% the memory necessary for the new Image structure and returns a pointer to
857% the new image.
858%
859% The format of the ReadMGKImage method is:
860%
861% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
862%
863% A description of each parameter follows:
864%
865% o image_info: the image info.
866%
867% o exception: return any errors or warnings in this structure.
868%
869*/
870static Image *ReadMGKImage(const ImageInfo *image_info,
871 ExceptionInfo *exception)
872{
873 char
874 buffer[MaxTextExtent];
875
876 Image
877 *image;
878
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]879 MagickBooleanType
880 status;
881
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]882 register PixelPacket
883 *q;
884
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]885 register size_t
886 x;
887
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]888 register unsigned char
889 *p;
890
891 ssize_t
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]892 count,
893 y;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]894
895 unsigned char
896 *pixels;
897
898 unsigned long
899 columns,
900 rows;
901
902 /*
903 Open image file.
904 */
905 assert(image_info != (const ImageInfo *) NULL);
906 assert(image_info-&gt;signature == MagickSignature);
907 if (image_info-&gt;debug != MagickFalse)
908 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
909 assert(exception != (ExceptionInfo *) NULL);
910 assert(exception-&gt;signature == MagickSignature);
911 image=AcquireImage(image_info);
912 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
913 if (status == MagickFalse)
914 {
915 image=DestroyImageList(image);
916 return((Image *) NULL);
917 }
918 /*
919 Read MGK image.
920 */
921 (void) ReadBlobString(image,buffer); /* read magic number */
922 if (IsMGK(buffer,7) == MagickFalse)
923 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
924 (void) ReadBlobString(image,buffer);
925 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
926 if (count &lt;= 0)
927 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
928 do
929 {
930 /*
931 Initialize image structure.
932 */
933 image-&gt;columns=columns;
934 image-&gt;rows=rows;
935 image-&gt;depth=8;
936 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
937 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
938 break;
939 /*
940 Convert MGK raster image to pixel packets.
941 */
942 if (SetImageExtent(image,0,0) == MagickFalse)
943 {
944 InheritException(exception,&amp;image-&gt;exception);
945 return(DestroyImageList(image));
946 }
947 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
948 if (pixels == (unsigned char *) NULL)
949 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]950 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]951 {
952 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
953 if (count != (ssize_t) (3*image-&gt;columns))
954 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
955 p=pixels;
956 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
957 if (q == (PixelPacket *) NULL)
958 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]959 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]960 {
961 q-&gt;red=ScaleCharToQuantum(*p++);
962 q-&gt;green=ScaleCharToQuantum(*p++);
963 q-&gt;blue=ScaleCharToQuantum(*p++);
964 q++;
965 }
966 if (SyncAuthenticPixels(image,exception) == MagickFalse)
967 break;
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]968 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]969 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
970 break;
971 }
972 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
973 if (EOFBlob(image) != MagickFalse)
974 {
975 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
976 break;
977 }
978 /*
979 Proceed to next image.
980 */
981 if (image_info-&gt;number_scenes != 0)
982 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
983 break;
984 *buffer='\0';
985 (void) ReadBlobString(image,buffer);
986 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
987 if (count != 0)
988 {
989 /*
990 Allocate next image structure.
991 */
992 AcquireNextImage(image_info,image);
993 if (GetNextImageInList(image) == (Image *) NULL)
994 {
995 image=DestroyImageList(image);
996 return((Image *) NULL);
997 }
998 image=SyncNextImageInList(image);
999 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
1000 if (status == MagickFalse)
1001 break;
1002 }
1003 } while (count != 0);
1004 (void) CloseBlob(image);
1005 return(GetFirstImageInList(image));
1006}
1007
1008/*
1009%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1010% %
1011% %
1012% %
1013% R e g i s t e r M G K I m a g e %
1014% %
1015% %
1016% %
1017%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1018%
1019% RegisterMGKImage() adds attributes for the MGK image format to
1020% the list of supported formats. The attributes include the image format
1021% tag, a method to read and/or write the format, whether the format
1022% supports the saving of more than one frame to the same file or blob,
1023% whether the format supports native in-memory I/O, and a brief
1024% description of the format.
1025%
1026% The format of the RegisterMGKImage method is:
1027%
1028% unsigned long RegisterMGKImage(void)
1029%
1030*/
1031ModuleExport unsigned long RegisterMGKImage(void)
1032{
1033 MagickInfo
1034 *entry;
1035
1036 entry=SetMagickInfo("MGK");
1037 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
1038 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
1039 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
1040 entry-&gt;description=ConstantString("MGK");
1041 entry-&gt;module=ConstantString("MGK");
1042 (void) RegisterMagickInfo(entry);
1043 return(MagickImageCoderSignature);
1044}
1045
1046/*
1047%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1048% %
1049% %
1050% %
1051% U n r e g i s t e r M G K I m a g e %
1052% %
1053% %
1054% %
1055%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1056%
1057% UnregisterMGKImage() removes format registrations made by the
1058% MGK module from the list of supported formats.
1059%
1060% The format of the UnregisterMGKImage method is:
1061%
1062% UnregisterMGKImage(void)
1063%
1064*/
1065ModuleExport void UnregisterMGKImage(void)
1066{
1067 (void) UnregisterMagickInfo("MGK");
1068}
1069
1070/*
1071%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1072% %
1073% %
1074% %
1075% W r i t e M G K I m a g e %
1076% %
1077% %
1078% %
1079%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1080%
1081% WriteMGKImage() writes an image to a file in red, green, and blue
1082% MGK rasterfile format.
1083%
1084% The format of the WriteMGKImage method is:
1085%
1086% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1087%
1088% A description of each parameter follows.
1089%
1090% o image_info: the image info.
1091%
1092% o image: The image.
1093%
1094*/
1095static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1096{
1097 char
1098 buffer[MaxTextExtent];
1099
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1100 MagickBooleanType
1101 status;
1102
1103 MagickOffsetType
1104 scene;
1105
1106 register const PixelPacket
1107 *p;
1108
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1109 register ssize_t
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1110 x;
1111
1112 register unsigned char
1113 *q;
1114
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1115 ssize_t
1116 y;
1117
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1118 unsigned char
1119 *pixels;
1120
1121 /*
1122 Open output image file.
1123 */
1124 assert(image_info != (const ImageInfo *) NULL);
1125 assert(image_info-&gt;signature == MagickSignature);
1126 assert(image != (Image *) NULL);
1127 assert(image-&gt;signature == MagickSignature);
1128 if (image-&gt;debug != MagickFalse)
1129 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1130 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1131 if (status == MagickFalse)
1132 return(status);
1133 scene=0;
1134 do
1135 {
1136 /*
1137 Allocate memory for pixels.
1138 */
1139 if (image-&gt;colorspace != RGBColorspace)
1140 (void) SetImageColorspace(image,RGBColorspace);
1141 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1142 3UL*sizeof(*pixels));
1143 if (pixels == (unsigned char *) NULL)
1144 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1145 /*
1146 Initialize raster file header.
1147 */
1148 (void) WriteBlobString(image,"id=mgk\n");
1149 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1150 image-&gt;columns,image-&gt;rows);
1151 (void) WriteBlobString(image,buffer);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1152 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1153 {
1154 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1155 if (p == (const PixelPacket *) NULL)
1156 break;
1157 q=pixels;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1158 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1159 {
1160 *q++=ScaleQuantumToChar(p-&gt;red);
1161 *q++=ScaleQuantumToChar(p-&gt;green);
1162 *q++=ScaleQuantumToChar(p-&gt;blue);
1163 p++;
1164 }
1165 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1166 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1167 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1168 break;
1169 }
1170 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1171 if (GetNextImageInList(image) == (Image *) NULL)
1172 break;
1173 image=SyncNextImageInList(image);
1174 status=SetImageProgress(image,SaveImagesTag,scene,
1175 GetImageListLength(image));
1176 if (status == MagickFalse)
1177 break;
1178 scene++;
1179 } while (image_info-&gt;adjoin != MagickFalse);
1180 (void) CloseBlob(image);
1181 return(MagickTrue);
1182}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1183</div>
1184
1185<p>To invoke the custom coder from the command line, use these commands:</p>
1186
1187<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>
1188<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>
1189
1190</div>
1191
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1192<h2><a id="filters"></a>Custom Image Filters</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1193<div class="doc-section">
1194
1195<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>
1196
1197<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>
1198
1199<div class="viewport">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1200#include &lt;stdio.h&gt;
1201#include &lt;stdlib.h&gt;
1202#include &lt;string.h&gt;
1203#include &lt;time.h&gt;
1204#include &lt;assert.h&gt;
1205#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1206#include "magick/MagickCore.h"
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1207
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1208/*
1209%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1210% %
1211% %
1212% %
1213% a n a l y z e I m a g e %
1214% %
1215% %
1216% %
1217%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1218%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1219% analyzeImage() computes the brightness and saturation mean, standard
cristy52923442011-01-15 22:54:31 +0000[diff] [blame^]1220% deviation, kurtosis and skewness and stores these values as attributes
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1221% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1222%
1223% The format of the analyzeImage method is:
1224%
1225% unsigned long analyzeImage(Image *images,const int argc,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1226% char **argv,ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1227%
1228% A description of each parameter follows:
1229%
1230% o image: the address of a structure of type Image.
1231%
1232% o argc: Specifies a pointer to an integer describing the number of
1233% elements in the argument vector.
1234%
1235% o argv: Specifies a pointer to a text array containing the command line
1236% arguments.
1237%
1238% o exception: return any errors or warnings in this structure.
1239%
1240*/
1241ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1242 const char **argv,ExceptionInfo *exception)
1243{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1244 char
1245 text[MaxTextExtent];
1246
1247 double
1248 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1249 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1250 brightness_mean,
1251 brightness_standard_deviation,
1252 brightness_kurtosis,
1253 brightness_skewness,
1254 brightness_sum_x,
1255 brightness_sum_x2,
1256 brightness_sum_x3,
1257 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1258 hue,
1259 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1260 saturation_mean,
1261 saturation_standard_deviation,
1262 saturation_kurtosis,
1263 saturation_skewness,
1264 saturation_sum_x,
1265 saturation_sum_x2,
1266 saturation_sum_x3,
1267 saturation_sum_x4;
1268
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1269 Image
1270 *image;
1271
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1272 assert(images != (Image **) NULL);
1273 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1274 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1275 (void) argc;
1276 (void) argv;
1277 image=(*images);
1278 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1279 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1280 CacheView
1281 *image_view;
1282
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1283 MagickBooleanType
1284 status;
1285
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1286 ssize_t
1287 y;
1288
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1289 brightness_sum_x=0.0;
1290 brightness_sum_x2=0.0;
1291 brightness_sum_x3=0.0;
1292 brightness_sum_x4=0.0;
1293 brightness_mean=0.0;
1294 brightness_standard_deviation=0.0;
1295 brightness_kurtosis=0.0;
1296 brightness_skewness=0.0;
1297 saturation_sum_x=0.0;
1298 saturation_sum_x2=0.0;
1299 saturation_sum_x3=0.0;
1300 saturation_sum_x4=0.0;
1301 saturation_mean=0.0;
1302 saturation_standard_deviation=0.0;
1303 saturation_kurtosis=0.0;
1304 saturation_skewness=0.0;
1305 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1306 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1307 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1308#if defined(MAGICKCORE_OPENMP_SUPPORT)
1309 #pragma omp parallel for schedule(dynamic,4) shared(status)
1310#endif
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1311 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1312 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1313 register const PixelPacket
1314 *p;
1315
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1316 register ssize_t
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1317 x;
1318
1319 if (status == MagickFalse)
1320 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1321 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1322 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1323 {
1324 status=MagickFalse;
1325 continue;
1326 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1327 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1328 {
1329 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1330 brightness*=QuantumRange;
1331 brightness_sum_x+=brightness;
1332 brightness_sum_x2+=brightness*brightness;
1333 brightness_sum_x3+=brightness*brightness*brightness;
1334 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1335 saturation*=QuantumRange;
1336 saturation_sum_x+=saturation;
1337 saturation_sum_x2+=saturation*saturation;
1338 saturation_sum_x3+=saturation*saturation*saturation;
1339 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1340 area++;
1341 p++;
1342 }
1343 }
1344 image_view=DestroyCacheView(image_view);
1345 if (area &lt;= 0.0)
1346 break;
1347 brightness_mean=brightness_sum_x/area;
1348 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1349 (void) SetImageProperty(image,"filter:brightness:mean",text);
1350 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1351 area*brightness_sum_x/area));
1352 (void) FormatMagickString(text,MaxTextExtent,"%g",
1353 brightness_standard_deviation);
1354 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1355 if (brightness_standard_deviation != 0)
1356 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1357 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1358 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1359 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1360 brightness_standard_deviation*brightness_standard_deviation*
1361 brightness_standard_deviation)-3.0;
1362 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1363 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1364 if (brightness_standard_deviation != 0)
1365 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1366 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1367 brightness_mean)/(brightness_standard_deviation*
1368 brightness_standard_deviation*brightness_standard_deviation);
1369 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1370 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1371 saturation_mean=saturation_sum_x/area;
1372 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1373 (void) SetImageProperty(image,"filter:saturation:mean",text);
1374 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1375 area*saturation_sum_x/area));
1376 (void) FormatMagickString(text,MaxTextExtent,"%g",
1377 saturation_standard_deviation);
1378 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1379 if (saturation_standard_deviation != 0)
1380 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1381 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1382 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1383 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1384 saturation_standard_deviation*saturation_standard_deviation*
1385 saturation_standard_deviation)-3.0;
1386 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1387 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1388 if (saturation_standard_deviation != 0)
1389 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1390 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1391 saturation_mean)/(saturation_standard_deviation*
1392 saturation_standard_deviation*saturation_standard_deviation);
1393 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1394 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1395 }
1396 return(MagickImageFilterSignature);
1397}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1398</div>
1399
1400<p>To invoke the custom filter from the command line, use this command:</p>
1401
1402<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/>
1403 Format: LOGO (ImageMagick Logo) <br/>
1404 Class: PseudoClass <br/>
1405 Geometry: 640x480 <br/>
1406 ... <br/>
1407 filter:brightness:kurtosis: 8.98864 <br/>
1408 filter:brightness:mean: 238.096 <br/>
1409 filter:brightness:skewness: -3.04519 <br/>
1410 filter:brightness:standard-deviation: 46.3286 <br/>
1411 filter:saturation:kurtosis: 5.9137 <br/>
1412 filter:saturation:mean: 23.4635 <br/>
1413 filter:saturation:skewness: 2.71874 <br/>
1414 filter:saturation:standard-deviation: 64.7734</span></p>
1415
1416<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>
1417
1418</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1419
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