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205
206<div class="main">
207
208
209
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]210<h1>The <em>Magick</em> Behind ImageMagick</h1>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]211<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]212
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cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]214<div class="doc-section">
215<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>
216</div>
217
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]218<h2><a id="overview"></a>Architecture Overview</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]219<div class="doc-section">
220
221<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>
222
223<ul>
224 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
225 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
226 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
227 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
228 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
229 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
230</ul>
231
232<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>
233
234<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
235
236<ul>
237 <li>one pixel a time (e.g. pixel at location 10,3)</li>
238 <li>a single scanline (e.g. all pixels from row 4)</li>
239 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
240 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
241 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
242 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
243 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
244 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
245 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
246 <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>
247 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]248 <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]249</ul>
250
251<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>
252
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]253<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]254
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]255<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]256
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]257<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]258
259</div>
260
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]261<h2><a id="cache"></a>The Pixel Cache</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]262<div class="doc-section">
263
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]264<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]265
266<h3>Create the Pixel Cache</h3>
267<div class="doc-section">
268
269<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>
270
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]271<dl>
272<dt>Create an image canvas initialized to the background color:</dt>
273<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]274 image=AllocateImage(image_info);
275 if (SetImageExtent(image,640,480) == MagickFalse)
276 { /* an exception was thrown */ }
277 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
278 SetImageBackgroundColor(image);
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]279</p></dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]280
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]281<dt>Create an image from a JPEG image on disk:</dt>
282<dd><p class="code">
283 (void) strcpy(image_info-&gt;filename,"image.jpg"):
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]284 image=ReadImage(image_info,exception);
285 if (image == (Image *) NULL)
286 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]287</p></dd>
288<dt>Create an image from a memory based image:</dt>
289<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]290 image=BlobToImage(blob_info,blob,extent,exception);
291 if (image == (Image *) NULL)
292 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]293</p></dd>
294</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]295
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]296<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]297
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]298<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]299
cristye6e84152011-06-06 14:16:49 +0000[diff] [blame^]300<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.7.0-4 2011-06-03 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]301<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]302</div>
303
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]304<h3><a id="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]305<div class="doc-section">
306
307<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>
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]308<ul>
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]309 <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]310 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
311 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
312 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]313</ul>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]314
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]315<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]316
317<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]318 const PixelPacket
319 *p;
320
321 PixelPacket
322 *q;
323
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]324 ssize_t
325 x,
326 y;
327
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]328 destination=CloneImage(source,source->columns,source->rows,MagickTrue,
329 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]330 if (destination == (Image *) NULL)
331 { /* an exception was thrown */ }
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,exception);
335 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
336 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
337 break;
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 {
340 q-&gt;red=90*p-&gt;red/100;
341 q-&gt;green=90*p-&gt;green/100;
342 q-&gt;blue=90*p-&gt;blue/100;
343 q-&gt;opacity=90*p-&gt;opacity/100;
344 p++;
345 q++;
346 }
347 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
348 break;
349 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]350 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]351 { /* an exception was thrown */ }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]352</div>
353
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]354<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]355
356<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>
357
358<pre class="code">
359 const IndexPacket
360 *indexes;
361
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]362 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]363 {
364 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
365 if (p == (const PixelPacket *) NULL)
366 break;
367 indexes=GetVirtualIndexes(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]368 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]369 (void) printf("%d\n",GetIndexPixelComponent(indexes+x));
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]370 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]371 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]372 /* an exception was thrown */
373</pre>
374
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]375<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]376
377<pre class="code">
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]378 p=GetVirtualPixels(source,-3,-3,source-&gt;columns+3,6,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]379</pre>
380
381<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
382</div>
383
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]384<h3><a id="virtual-pixels"></a>Virtual Pixels</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]385<div class="doc-section">
386
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]387<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]388 <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>
389
cristy4c54bbb2011-03-17 13:53:13 +0000[diff] [blame]390<pre class="text" style="font-size: 83.3333%;">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]391 background: the area surrounding the image is the background color
392 black: the area surrounding the image is black
393 checker-tile: alternate squares with image and background color
394 dither: non-random 32x32 dithered pattern
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]395 edge: extend the edge pixel toward infinity (default)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]396 gray: the area surrounding the image is gray
397 horizontal-tile: horizontally tile the image, background color above/below
398 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
399 mirror: mirror tile the image
400 random: choose a random pixel from the image
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]401 tile: tile the image
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]402 transparent: the area surrounding the image is transparent blackness
403 vertical-tile: vertically tile the image, sides are background color
404 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
405 white: the area surrounding the image is white
406</pre>
407
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]408</div>
409
410<h3>Cache Storage and Resource Requirements</h3>
411<div class="doc-section">
412
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]413<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]414
415<dl class="doc">
416 <dt class="doc">files</dt>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]417 <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]418 <dt class="doc">area</dt>
419 <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>
420 <dt class="doc">memory</dt>
421 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
422 <dt class="doc">map</dt>
423 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
424 <dt class="doc">disk</dt>
425 <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]426 <dt class="doc">thread</dt>
427 <dd>maximum number of threads that are permitted to run in parallel.</dd>
428 <dt class="doc">time</dt>
429 <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]430</dl>
431
432<p>To determine the current setting of these limits, use this command:</p>
433
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]434<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span></p><pre class="text">
435File Area Memory Map Disk Thread Time
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]436-------------------------------------------------------------------------------
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]437 768 1.0386GB 3.8692GiB 7.7384GiB unlimited 4 unlimited
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]438</pre>
439
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]440<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]441
442<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>
443</div>
444
445<h3>Cache Views</h3>
446<div class="doc-section">
447
448<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>
449
450<pre class="code">
451 CacheView
452 *view_1,
453 *view_2;
454
cristye9a32c32011-04-07 01:11:05 +0000[diff] [blame]455 view_1=AcquireCacheView(source);
456 view_2=AcquireCacheView(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]457 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]458 {
459 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]460 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,
461 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]462 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
463 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]464 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]465 {
466 /* do something with u &amp; v here */
467 }
468 }
cristye9a32c32011-04-07 01:11:05 +0000[diff] [blame]469 view_2=DestroyCacheView(view_2);
470 view_1=DestroyCacheView(view_1);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]471 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]472 { /* an exception was thrown */ }
473</pre>
474</div>
475
476<h3>Magick Persistent Cache Format</h3>
477<div class="doc-section">
478
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]479<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]480<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]481</div>
482
483<h3>Best Practices</h3>
484<div class="doc-section">
485
cristy30092792011-02-22 02:06:14 +0000[diff] [blame]486<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. Although you can access scanlines of pixels sequentially from the last row of the image to the first, you may get a perfomance boost if you access scanlines from the first row of the image to the last, in sequentual order.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]487
488<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>
489
490<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>
491
492<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>
493
494<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>
495
496<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>
497
498<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>
499
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]500<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]501
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]502<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]503
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]504<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]505
506<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>
507
508<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>
509<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>
510</div>
511
512</div>
513
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]514<h2><a id="stream"></a>Streaming Pixels</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]515<div class="doc-section">
516
517<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>
518
519<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>
520
521<pre class="code">
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]522static size_t StreamPixels(const Image *image,const void *pixels,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]523 const size_t columns)
524{
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]525 register const PixelPacket
526 *p;
527
528 MyData
529 *my_data;
530
531 my_data=(MyData *) image->client_data;
532 p=(PixelPacket *) pixels;
533 if (p != (const PixelPacket *) NULL)
534 {
535 /* process pixels here */
536 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]537 return(columns);
538}
539
540...
541/* invoke the pixel stream here */
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]542image_info->client_data=(void *) MyData;
543image=ReadStream(image_info,&amp;StreamPixels,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]544</pre>
545
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]546<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. A majority of the image formats stream pixels (red, green, and blue) from left to right and top to bottom. However, a few formats do not support this common ordering (e.g. the PSD format).</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]547
548</div>
549
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]550<h2><a id="properties"></a>Image Properties and Profiles</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]551<div class="doc-section">
552
553<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>
554
555<pre class="code">
556 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
557</pre>
558
559<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>
560
561<pre class="code">
562 const char
563 *comment;
564
565 (void) SetImageProperty(image,"comment","This space for rent");
566 comment=GetImageProperty(image,"comment");
567 if (comment == (const char *) NULL)
568 (void) printf("Image comment: %s\n",comment);
569</pre>
570
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]571<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]572
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]573<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>
574
575<pre class="code">
576 StringInfo
577 *profile;
578
579 profile=AcquireStringInfo(length);
580 SetStringInfoDatum(profile,my_exif_profile);
581 (void) SetImageProfile(image,"EXIF",profile);
582 DestroyStringInfo(profile);
583 profile=GetImageProfile(image,"EXIF");
584 if (profile != (StringInfo *) NULL)
585 (void) PrintStringInfo(stdout,"EXIF",profile);
586</pre>
587
588</div>
589
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]590<h2><a id="tera-pixel"></a>Large Image Support</h2>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]591<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]592<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]593
594<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]595<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]596
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]597<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]598<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>
599
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]600<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]601<p>Here we force all image pixels to disk:</p>
602
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]603<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]604<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]605
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]606<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]607
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]608<h2><a id="threads"></a>Threads of Execution</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]609<div class="doc-section">
610
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]611<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]612
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]613<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]614
615<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]616{
617 CacheView
618 *image_view;
619
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]620 MagickBooleanType
621 status;
622
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]623 ssize_t
624 y;
625
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]626 status=MagickTrue;
627 image_view=AcquireCacheView(image);
628 #pragma omp parallel for schedule(dynamic,4) shared(status)
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]629 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]630 {
631 register IndexPacket
632 *indexes;
633
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]634 register PixelPacket
635 *q;
636
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]637 register ssize_t
638 x;
639
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]640 if (status == MagickFalse)
641 continue;
642 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
643 if (q == (PixelPacket *) NULL)
644 {
645 status=MagickFalse;
646 continue;
647 }
648 indexes=GetCacheViewAuthenticIndexQueue(image_view);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]649 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]650 {
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]651 SetRedPixelComponent(q,...);
652 SetGreenPixelComponent(q,...);
653 SetBluePixelComponent(q,...);
654 SetOpacityPixelComponent(q,...);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]655 if (indexes != (IndexPacket *) NULL)
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]656 SetIndexPixelComponent(indexes+x,...);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]657 q++;
658 }
659 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
660 status=MagickFalse;
661 }
662 image_view=DestroyCacheView(image_view);
663 if (status == MagickFalse)
664 perror("something went wrong");
665}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]666</div>
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]667<p>This code snippet converts an uncompressed Windows bitmap to a Magick++ image:</p>
668<div class="viewport">
669#include "Magick++.h"
670#include &lt;assert.h&gt;
671#include "omp.h"
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]672
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]673void ConvertBMPToImage(const BITMAPINFOHEADER *bmp_info,
674 const unsigned char *restrict pixels,Magick::Image *image)
675{
676 /*
677 Prepare the image so that we can modify the pixels directly.
678 */
679 assert(bmp_info->biCompression == BI_RGB);
680 assert(bmp_info->biWidth == image->columns());
681 assert(abs(bmp_info->biHeight) == image->rows());
682 image->modifyImage();
683 if (bmp_info->biBitCount == 24)
684 image->type(MagickCore::TrueColorType);
685 else
686 image->type(MagickCore::TrueColorMatteType);
687 register unsigned int bytes_per_row=bmp_info->biWidth*bmp_info->biBitCount/8;
688 if (bytes_per_row % 4 != 0) {
689 bytes_per_row=bytes_per_row+(4-bytes_per_row % 4); // divisible by 4.
690 }
691 /*
692 Copy all pixel data, row by row.
693 */
694 #pragma omp parallel for
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]695 for (int y=0; y &lt; int(image->rows()); y++)
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]696 {
697 int row=(bmp_info->biHeight > 0) ? (image->rows()-y-1) : y;
698 register const unsigned char *restrict p=pixels+row*bytes_per_row;
699 register MagickCore::PixelPacket *restrict q=
700 image->setPixels(0,y,image->columns(),1);
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]701 for (int x=0; x &lt; int(image->columns()); x++)
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]702 {
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]703 SetBluePixelComponent(q,p[0]);
704 SetGreenPixelComponent(q,p[1]);
705 SetRedPixelComponent(q,p[2]);
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]706 if (bmp_info->biBitCount == 32) {
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]707 SetOpacityPixelComponent(q,p[3]);
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]708 }
709 q++;
710 p+=bmp_info->biBitCount/8;
711 }
712 image->syncPixels(); // sync pixels to pixel cache.
713 }
714 return;
715}
716</div>
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]717
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]718<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>
719
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]720<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]721
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]722<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]723
724<pre class="text">
725 &lt;policy domain="resource" name="thread" value="2"/>
726</pre>
727
728<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>
729
730<pre class="text">
731 export MAGICK_THREAD_LIMIT=12
732</pre>
733
734<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>
735
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]736</div>
737
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]738<h2><a id="distributed"></a>Heterogeneous Distributed Processing</h2>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]739<div class="doc-section">
740<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>
741
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]742<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]743
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]744<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
745<p>If so, run this command to realize a significant speed-up for image convolution:</p>
746
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]747<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]748<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
749
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]750<p>Here is an example OpenCL kernel that convolves an image:</p>
751
752<div class="viewport">
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]753static inline long ClampToCanvas(const long offset,const ulong range)
754{
755 if (offset &lt; 0L)
756 return(0L);
757 if (offset >= range)
758 return((long) (range-1L));
759 return(offset);
760}
761
762static inline CLQuantum ClampToQuantum(const double value)
763{
764 if (value &lt; 0.0)
765 return((CLQuantum) 0);
766 if (value >= (double) QuantumRange)
767 return((CLQuantum) QuantumRange);
768 return((CLQuantum) (value+0.5));
769}
770
771__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
772 const ulong width,const ulong height,__global CLPixelType *destination)
773{
774 const ulong columns = get_global_size(0);
775 const ulong rows = get_global_size(1);
776
777 const long x = get_global_id(0);
778 const long y = get_global_id(1);
779
780 const double scale = (1.0/QuantumRange);
781 const long mid_width = (width-1)/2;
782 const long mid_height = (height-1)/2;
783 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
784 double gamma = 0.0;
785 register ulong i = 0;
786
787 for (long v=(-mid_height); v &lt;= mid_height; v++)
788 {
789 for (long u=(-mid_width); u &lt;= mid_width; u++)
790 {
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]791 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,
792 columns);
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]793 const double alpha=scale*(QuantumRange-source[index].w);
794 sum.x+=alpha*filter[i]*source[index].x;
795 sum.y+=alpha*filter[i]*source[index].y;
796 sum.z+=alpha*filter[i]*source[index].z;
797 sum.w+=filter[i]*source[index].w;
798 gamma+=alpha*filter[i];
799 i++;
800 }
801 }
802
803 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
804 const ulong index=y*columns+x;
805 destination[index].x=ClampToQuantum(gamma*sum.x);
806 destination[index].y=ClampToQuantum(gamma*sum.y);
807 destination[index].z=ClampToQuantum(gamma*sum.z);
808 destination[index].w=ClampToQuantum(sum.w);
809};
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]810</div>
811
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]812<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]813
814</div>
815
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]816<h2><a id="coders"></a>Custom Image Coders</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]817<div class="doc-section">
818
819<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>
820
821<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>
822
823<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]824/*
825 Include declarations.
826*/
827#include "magick/studio.h"
828#include "magick/blob.h"
829#include "magick/blob-private.h"
830#include "magick/colorspace.h"
831#include "magick/exception.h"
832#include "magick/exception-private.h"
833#include "magick/image.h"
834#include "magick/image-private.h"
835#include "magick/list.h"
836#include "magick/magick.h"
837#include "magick/memory_.h"
838#include "magick/monitor.h"
839#include "magick/monitor-private.h"
840#include "magick/quantum-private.h"
841#include "magick/static.h"
842#include "magick/string_.h"
843#include "magick/module.h"
844
845/*
846 Forward declarations.
847*/
848static MagickBooleanType
849 WriteMGKImage(const ImageInfo *,Image *);
850
851/*
852%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
853% %
854% %
855% %
856% I s M G K %
857% %
858% %
859% %
860%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
861%
862% IsMGK() returns MagickTrue if the image format type, identified by the
863% magick string, is MGK.
864%
865% The format of the IsMGK method is:
866%
867% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
868%
869% A description of each parameter follows:
870%
871% o magick: This string is generally the first few bytes of an image file
872% or blob.
873%
874% o length: Specifies the length of the magick string.
875%
876*/
877static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
878{
879 if (length &lt; 7)
880 return(MagickFalse);
881 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
882 return(MagickTrue);
883 return(MagickFalse);
884}
885
886/*
887%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
888% %
889% %
890% %
891% R e a d M G K I m a g e %
892% %
893% %
894% %
895%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
896%
897% ReadMGKImage() reads a MGK image file and returns it. It allocates
898% the memory necessary for the new Image structure and returns a pointer to
899% the new image.
900%
901% The format of the ReadMGKImage method is:
902%
903% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
904%
905% A description of each parameter follows:
906%
907% o image_info: the image info.
908%
909% o exception: return any errors or warnings in this structure.
910%
911*/
912static Image *ReadMGKImage(const ImageInfo *image_info,
913 ExceptionInfo *exception)
914{
915 char
916 buffer[MaxTextExtent];
917
918 Image
919 *image;
920
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]921 MagickBooleanType
922 status;
923
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]924 register PixelPacket
925 *q;
926
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]927 register size_t
928 x;
929
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]930 register unsigned char
931 *p;
932
933 ssize_t
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]934 count,
935 y;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]936
937 unsigned char
938 *pixels;
939
940 unsigned long
941 columns,
942 rows;
943
944 /*
945 Open image file.
946 */
947 assert(image_info != (const ImageInfo *) NULL);
948 assert(image_info-&gt;signature == MagickSignature);
949 if (image_info-&gt;debug != MagickFalse)
950 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
951 assert(exception != (ExceptionInfo *) NULL);
952 assert(exception-&gt;signature == MagickSignature);
953 image=AcquireImage(image_info);
954 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
955 if (status == MagickFalse)
956 {
957 image=DestroyImageList(image);
958 return((Image *) NULL);
959 }
960 /*
961 Read MGK image.
962 */
963 (void) ReadBlobString(image,buffer); /* read magic number */
964 if (IsMGK(buffer,7) == MagickFalse)
965 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
966 (void) ReadBlobString(image,buffer);
967 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
968 if (count &lt;= 0)
969 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
970 do
971 {
972 /*
973 Initialize image structure.
974 */
975 image-&gt;columns=columns;
976 image-&gt;rows=rows;
977 image-&gt;depth=8;
978 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
979 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
980 break;
981 /*
982 Convert MGK raster image to pixel packets.
983 */
984 if (SetImageExtent(image,0,0) == MagickFalse)
985 {
986 InheritException(exception,&amp;image-&gt;exception);
987 return(DestroyImageList(image));
988 }
989 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
990 if (pixels == (unsigned char *) NULL)
991 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]992 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]993 {
994 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
995 if (count != (ssize_t) (3*image-&gt;columns))
996 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
997 p=pixels;
998 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
999 if (q == (PixelPacket *) NULL)
1000 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1001 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1002 {
1003 q-&gt;red=ScaleCharToQuantum(*p++);
1004 q-&gt;green=ScaleCharToQuantum(*p++);
1005 q-&gt;blue=ScaleCharToQuantum(*p++);
1006 q++;
1007 }
1008 if (SyncAuthenticPixels(image,exception) == MagickFalse)
1009 break;
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1010 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1011 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
1012 break;
1013 }
1014 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1015 if (EOFBlob(image) != MagickFalse)
1016 {
1017 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
1018 break;
1019 }
1020 /*
1021 Proceed to next image.
1022 */
1023 if (image_info-&gt;number_scenes != 0)
1024 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
1025 break;
1026 *buffer='\0';
1027 (void) ReadBlobString(image,buffer);
1028 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
1029 if (count != 0)
1030 {
1031 /*
1032 Allocate next image structure.
1033 */
1034 AcquireNextImage(image_info,image);
1035 if (GetNextImageInList(image) == (Image *) NULL)
1036 {
1037 image=DestroyImageList(image);
1038 return((Image *) NULL);
1039 }
1040 image=SyncNextImageInList(image);
1041 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
1042 if (status == MagickFalse)
1043 break;
1044 }
1045 } while (count != 0);
1046 (void) CloseBlob(image);
1047 return(GetFirstImageInList(image));
1048}
1049
1050/*
1051%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1052% %
1053% %
1054% %
1055% R e g i s t e r M G K I m a g e %
1056% %
1057% %
1058% %
1059%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1060%
1061% RegisterMGKImage() adds attributes for the MGK image format to
1062% the list of supported formats. The attributes include the image format
1063% tag, a method to read and/or write the format, whether the format
1064% supports the saving of more than one frame to the same file or blob,
1065% whether the format supports native in-memory I/O, and a brief
1066% description of the format.
1067%
1068% The format of the RegisterMGKImage method is:
1069%
1070% unsigned long RegisterMGKImage(void)
1071%
1072*/
1073ModuleExport unsigned long RegisterMGKImage(void)
1074{
1075 MagickInfo
1076 *entry;
1077
1078 entry=SetMagickInfo("MGK");
1079 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
1080 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
1081 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
1082 entry-&gt;description=ConstantString("MGK");
1083 entry-&gt;module=ConstantString("MGK");
1084 (void) RegisterMagickInfo(entry);
1085 return(MagickImageCoderSignature);
1086}
1087
1088/*
1089%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1090% %
1091% %
1092% %
1093% U n r e g i s t e r M G K I m a g e %
1094% %
1095% %
1096% %
1097%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1098%
1099% UnregisterMGKImage() removes format registrations made by the
1100% MGK module from the list of supported formats.
1101%
1102% The format of the UnregisterMGKImage method is:
1103%
1104% UnregisterMGKImage(void)
1105%
1106*/
1107ModuleExport void UnregisterMGKImage(void)
1108{
1109 (void) UnregisterMagickInfo("MGK");
1110}
1111
1112/*
1113%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1114% %
1115% %
1116% %
1117% W r i t e M G K I m a g e %
1118% %
1119% %
1120% %
1121%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1122%
1123% WriteMGKImage() writes an image to a file in red, green, and blue
1124% MGK rasterfile format.
1125%
1126% The format of the WriteMGKImage method is:
1127%
1128% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1129%
1130% A description of each parameter follows.
1131%
1132% o image_info: the image info.
1133%
1134% o image: The image.
1135%
1136*/
1137static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1138{
1139 char
1140 buffer[MaxTextExtent];
1141
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1142 MagickBooleanType
1143 status;
1144
1145 MagickOffsetType
1146 scene;
1147
1148 register const PixelPacket
1149 *p;
1150
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1151 register ssize_t
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1152 x;
1153
1154 register unsigned char
1155 *q;
1156
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1157 ssize_t
1158 y;
1159
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1160 unsigned char
1161 *pixels;
1162
1163 /*
1164 Open output image file.
1165 */
1166 assert(image_info != (const ImageInfo *) NULL);
1167 assert(image_info-&gt;signature == MagickSignature);
1168 assert(image != (Image *) NULL);
1169 assert(image-&gt;signature == MagickSignature);
1170 if (image-&gt;debug != MagickFalse)
1171 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1172 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1173 if (status == MagickFalse)
1174 return(status);
1175 scene=0;
1176 do
1177 {
1178 /*
1179 Allocate memory for pixels.
1180 */
1181 if (image-&gt;colorspace != RGBColorspace)
1182 (void) SetImageColorspace(image,RGBColorspace);
1183 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1184 3UL*sizeof(*pixels));
1185 if (pixels == (unsigned char *) NULL)
1186 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1187 /*
1188 Initialize raster file header.
1189 */
1190 (void) WriteBlobString(image,"id=mgk\n");
1191 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1192 image-&gt;columns,image-&gt;rows);
1193 (void) WriteBlobString(image,buffer);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1194 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1195 {
1196 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1197 if (p == (const PixelPacket *) NULL)
1198 break;
1199 q=pixels;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1200 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1201 {
1202 *q++=ScaleQuantumToChar(p-&gt;red);
1203 *q++=ScaleQuantumToChar(p-&gt;green);
1204 *q++=ScaleQuantumToChar(p-&gt;blue);
1205 p++;
1206 }
1207 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1208 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1209 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1210 break;
1211 }
1212 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1213 if (GetNextImageInList(image) == (Image *) NULL)
1214 break;
1215 image=SyncNextImageInList(image);
1216 status=SetImageProgress(image,SaveImagesTag,scene,
1217 GetImageListLength(image));
1218 if (status == MagickFalse)
1219 break;
1220 scene++;
1221 } while (image_info-&gt;adjoin != MagickFalse);
1222 (void) CloseBlob(image);
1223 return(MagickTrue);
1224}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1225</div>
1226
1227<p>To invoke the custom coder from the command line, use these commands:</p>
1228
1229<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>
1230<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>
1231
1232</div>
1233
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1234<h2><a id="filters"></a>Custom Image Filters</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1235<div class="doc-section">
1236
1237<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>
1238
1239<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>
1240
1241<div class="viewport">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1242#include &lt;stdio.h&gt;
1243#include &lt;stdlib.h&gt;
1244#include &lt;string.h&gt;
1245#include &lt;time.h&gt;
1246#include &lt;assert.h&gt;
1247#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1248#include "magick/MagickCore.h"
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1249
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1250/*
1251%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1252% %
1253% %
1254% %
1255% a n a l y z e I m a g e %
1256% %
1257% %
1258% %
1259%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1260%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1261% analyzeImage() computes the brightness and saturation mean, standard
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]1262% deviation, kurtosis and skewness and stores these values as attributes
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1263% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1264%
1265% The format of the analyzeImage method is:
1266%
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1267% size_t analyzeImage(Image *images,const int argc,char **argv,
1268% ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1269%
1270% A description of each parameter follows:
1271%
1272% o image: the address of a structure of type Image.
1273%
1274% o argc: Specifies a pointer to an integer describing the number of
1275% elements in the argument vector.
1276%
1277% o argv: Specifies a pointer to a text array containing the command line
1278% arguments.
1279%
1280% o exception: return any errors or warnings in this structure.
1281%
1282*/
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1283ModuleExport size_t analyzeImage(Image **images,const int argc,const char **argv,
1284 ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1285{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1286 char
1287 text[MaxTextExtent];
1288
1289 double
1290 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1291 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1292 brightness_mean,
1293 brightness_standard_deviation,
1294 brightness_kurtosis,
1295 brightness_skewness,
1296 brightness_sum_x,
1297 brightness_sum_x2,
1298 brightness_sum_x3,
1299 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1300 hue,
1301 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1302 saturation_mean,
1303 saturation_standard_deviation,
1304 saturation_kurtosis,
1305 saturation_skewness,
1306 saturation_sum_x,
1307 saturation_sum_x2,
1308 saturation_sum_x3,
1309 saturation_sum_x4;
1310
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1311 Image
1312 *image;
1313
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1314 assert(images != (Image **) NULL);
1315 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1316 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1317 (void) argc;
1318 (void) argv;
1319 image=(*images);
1320 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1321 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1322 CacheView
1323 *image_view;
1324
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1325 MagickBooleanType
1326 status;
1327
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1328 ssize_t
1329 y;
1330
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1331 brightness_sum_x=0.0;
1332 brightness_sum_x2=0.0;
1333 brightness_sum_x3=0.0;
1334 brightness_sum_x4=0.0;
1335 brightness_mean=0.0;
1336 brightness_standard_deviation=0.0;
1337 brightness_kurtosis=0.0;
1338 brightness_skewness=0.0;
1339 saturation_sum_x=0.0;
1340 saturation_sum_x2=0.0;
1341 saturation_sum_x3=0.0;
1342 saturation_sum_x4=0.0;
1343 saturation_mean=0.0;
1344 saturation_standard_deviation=0.0;
1345 saturation_kurtosis=0.0;
1346 saturation_skewness=0.0;
1347 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1348 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1349 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1350#if defined(MAGICKCORE_OPENMP_SUPPORT)
1351 #pragma omp parallel for schedule(dynamic,4) shared(status)
1352#endif
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1353 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1354 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1355 register const PixelPacket
1356 *p;
1357
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1358 register ssize_t
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1359 x;
1360
1361 if (status == MagickFalse)
1362 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1363 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1364 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1365 {
1366 status=MagickFalse;
1367 continue;
1368 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1369 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1370 {
1371 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1372 brightness*=QuantumRange;
1373 brightness_sum_x+=brightness;
1374 brightness_sum_x2+=brightness*brightness;
1375 brightness_sum_x3+=brightness*brightness*brightness;
1376 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1377 saturation*=QuantumRange;
1378 saturation_sum_x+=saturation;
1379 saturation_sum_x2+=saturation*saturation;
1380 saturation_sum_x3+=saturation*saturation*saturation;
1381 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1382 area++;
1383 p++;
1384 }
1385 }
1386 image_view=DestroyCacheView(image_view);
1387 if (area &lt;= 0.0)
1388 break;
1389 brightness_mean=brightness_sum_x/area;
1390 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1391 (void) SetImageProperty(image,"filter:brightness:mean",text);
1392 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1393 area*brightness_sum_x/area));
1394 (void) FormatMagickString(text,MaxTextExtent,"%g",
1395 brightness_standard_deviation);
1396 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1397 if (brightness_standard_deviation != 0)
1398 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1399 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1400 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1401 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1402 brightness_standard_deviation*brightness_standard_deviation*
1403 brightness_standard_deviation)-3.0;
1404 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1405 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1406 if (brightness_standard_deviation != 0)
1407 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1408 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1409 brightness_mean)/(brightness_standard_deviation*
1410 brightness_standard_deviation*brightness_standard_deviation);
1411 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1412 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1413 saturation_mean=saturation_sum_x/area;
1414 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1415 (void) SetImageProperty(image,"filter:saturation:mean",text);
1416 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1417 area*saturation_sum_x/area));
1418 (void) FormatMagickString(text,MaxTextExtent,"%g",
1419 saturation_standard_deviation);
1420 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1421 if (saturation_standard_deviation != 0)
1422 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1423 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1424 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1425 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1426 saturation_standard_deviation*saturation_standard_deviation*
1427 saturation_standard_deviation)-3.0;
1428 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1429 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1430 if (saturation_standard_deviation != 0)
1431 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1432 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1433 saturation_mean)/(saturation_standard_deviation*
1434 saturation_standard_deviation*saturation_standard_deviation);
1435 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1436 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1437 }
1438 return(MagickImageFilterSignature);
1439}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1440</div>
1441
1442<p>To invoke the custom filter from the command line, use this command:</p>
1443
cristy323f35b2011-03-24 23:05:13 +0000[diff] [blame]1444<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/>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1445 Format: LOGO (ImageMagick Logo) <br/>
1446 Class: PseudoClass <br/>
1447 Geometry: 640x480 <br/>
1448 ... <br/>
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1449 filter:brightness:kurtosis: 8.17947 <br/>
1450 filter:brightness:mean: 60632.1 <br/>
1451 filter:brightness:skewness: -2.97118 <br/>
1452 filter:brightness:standard-deviation: 13742.1 <br/>
1453 filter:saturation:kurtosis: 4.33554 <br/>
1454 filter:saturation:mean: 5951.55 <br/>
1455 filter:saturation:skewness: 2.42848 <br/>
1456 filter:saturation:standard-deviation: 15575.9</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1457
1458<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>
1459
1460</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1461
1462</div>
1463
1464<div id="linkbar">
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]1465 <span id="linkbar-west">&nbsp;</span>
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1467 <a href="http://www.imagemagick.org/discourse-server/">Discourse Server</a> &bull;
cristya8902942010-07-30 00:49:52 +0000[diff] [blame]1468 <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">Studio</a>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1469 </span>
1470 <span id="linkbar-east">&nbsp;</span>
1471 </div>
1472 <div class="footer">
cristy7e41fe82010-12-04 23:12:08 +0000[diff] [blame]1473 <span id="footer-west">&copy; 1999-2011 ImageMagick Studio LLC</span>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1474 <span id="footer-east"> <a href="http://www.imagemagick.org/script/contact.php">Contact the Wizards</a></span>
1475 </div>
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cristya8902942010-07-30 00:49:52 +0000[diff] [blame]1477 <script type="text/javascript">
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