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193
194<div class="main">
195
196
197
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]198<h1>The <em>Magick</em> Behind ImageMagick</h1>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]199<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]200
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]201
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]202<div class="doc-section">
203<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>
204</div>
205
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]206<h2><a id="overview"></a>Architecture Overview</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]207<div class="doc-section">
208
209<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>
210
211<ul>
212 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
213 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
214 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
215 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
216 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
217 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
218</ul>
219
220<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>
221
222<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
223
224<ul>
225 <li>one pixel a time (e.g. pixel at location 10,3)</li>
226 <li>a single scanline (e.g. all pixels from row 4)</li>
227 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
228 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
229 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
230 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
231 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
232 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
233 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
234 <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>
235 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]236 <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]237</ul>
238
239<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>
240
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]241<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]242
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]243<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]244
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]245<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]246
247</div>
248
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]249<h2><a id="cache"></a>The Pixel Cache</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]250<div class="doc-section">
251
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]252<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]253
254<h3>Create the Pixel Cache</h3>
255<div class="doc-section">
256
257<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>
258
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]259<dl>
260<dt>Create an image canvas initialized to the background color:</dt>
261<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]262 image=AllocateImage(image_info);
263 if (SetImageExtent(image,640,480) == MagickFalse)
264 { /* an exception was thrown */ }
265 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
266 SetImageBackgroundColor(image);
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]267</p></dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]268
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]269<dt>Create an image from a JPEG image on disk:</dt>
270<dd><p class="code">
271 (void) strcpy(image_info-&gt;filename,"image.jpg"):
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]272 image=ReadImage(image_info,exception);
273 if (image == (Image *) NULL)
274 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]275</p></dd>
276<dt>Create an image from a memory based image:</dt>
277<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]278 image=BlobToImage(blob_info,blob,extent,exception);
279 if (image == (Image *) NULL)
280 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]281</p></dd>
282</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]283
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]284<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]285
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]286<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]287
cristy07249c72011-02-20 17:07:52 +0000[diff] [blame]288<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.7-8 2011-02-19 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]289<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]290</div>
291
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]292<h3><a id="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]293<div class="doc-section">
294
295<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]296<ul>
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]297 <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]298 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
299 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
300 <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]301</ul>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]302
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]303<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]304
305<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]306 const PixelPacket
307 *p;
308
309 PixelPacket
310 *q;
311
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]312 ssize_t
313 x,
314 y;
315
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]316 destination=CloneImage(source,source->columns,source->rows,MagickTrue,
317 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]318 if (destination == (Image *) NULL)
319 { /* an exception was thrown */ }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]320 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]321 {
322 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
323 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
324 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
325 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]326 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]327 {
328 q-&gt;red=90*p-&gt;red/100;
329 q-&gt;green=90*p-&gt;green/100;
330 q-&gt;blue=90*p-&gt;blue/100;
331 q-&gt;opacity=90*p-&gt;opacity/100;
332 p++;
333 q++;
334 }
335 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
336 break;
337 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]338 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]339 { /* an exception was thrown */ }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]340</div>
341
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]342<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]343
344<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>
345
346<pre class="code">
347 const IndexPacket
348 *indexes;
349
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]350 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]351 {
352 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
353 if (p == (const PixelPacket *) NULL)
354 break;
355 indexes=GetVirtualIndexes(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]356 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]357 (void) printf("%d\n",indexes[x];
358 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]359 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]360 /* an exception was thrown */
361</pre>
362
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]363<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]364
365<pre class="code">
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]366 p=GetVirtualPixels(source,-3,-3,source-&gt;columns+3,6,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]367</pre>
368
369<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
370</div>
371
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]372<h3><a id="virtual-pixels"></a>Virtual Pixels</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]373<div class="doc-section">
374
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]375<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]376 <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>
377
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]378<pre class="text" style="font-size: 90%;">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]379 background: the area surrounding the image is the background color
380 black: the area surrounding the image is black
381 checker-tile: alternate squares with image and background color
382 dither: non-random 32x32 dithered pattern
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]383 edge: extend the edge pixel toward infinity (default)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]384 gray: the area surrounding the image is gray
385 horizontal-tile: horizontally tile the image, background color above/below
386 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
387 mirror: mirror tile the image
388 random: choose a random pixel from the image
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]389 tile: tile the image
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]390 transparent: the area surrounding the image is transparent blackness
391 vertical-tile: vertically tile the image, sides are background color
392 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
393 white: the area surrounding the image is white
394</pre>
395
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]396</div>
397
398<h3>Cache Storage and Resource Requirements</h3>
399<div class="doc-section">
400
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]401<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]402
403<dl class="doc">
404 <dt class="doc">files</dt>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]405 <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]406 <dt class="doc">area</dt>
407 <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>
408 <dt class="doc">memory</dt>
409 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
410 <dt class="doc">map</dt>
411 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
412 <dt class="doc">disk</dt>
413 <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]414 <dt class="doc">thread</dt>
415 <dd>maximum number of threads that are permitted to run in parallel.</dd>
416 <dt class="doc">time</dt>
417 <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]418</dl>
419
420<p>To determine the current setting of these limits, use this command:</p>
421
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]422<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span></p><pre class="text">
423File Area Memory Map Disk Thread Time
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]424-------------------------------------------------------------------------------
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]425 768 1.0386GB 3.8692GiB 7.7384GiB unlimited 4 unlimited
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]426</pre>
427
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]428<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]429
430<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>
431</div>
432
433<h3>Cache Views</h3>
434<div class="doc-section">
435
436<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>
437
438<pre class="code">
439 CacheView
440 *view_1,
441 *view_2;
442
443 view_1=OpenCacheView(source);
444 view_2=OpenCacheView(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]445 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]446 {
447 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]448 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,
449 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]450 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
451 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]452 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]453 {
454 /* do something with u &amp; v here */
455 }
456 }
457 view_1=CloseCacheView(view_1);
458 view_2=CloseCacheView(view_2);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]459 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]460 { /* an exception was thrown */ }
461</pre>
462</div>
463
464<h3>Magick Persistent Cache Format</h3>
465<div class="doc-section">
466
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]467<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]468<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]469</div>
470
471<h3>Best Practices</h3>
472<div class="doc-section">
473
cristy30092792011-02-22 02:06:14 +0000[diff] [blame^]474<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]475
476<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>
477
478<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>
479
480<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>
481
482<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>
483
484<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>
485
486<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>
487
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]488<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]489
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]490<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]491
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]492<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]493
494<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>
495
496<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>
497<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>
498</div>
499
500</div>
501
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]502<h2><a id="stream"></a>Streaming Pixels</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]503<div class="doc-section">
504
505<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>
506
507<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>
508
509<pre class="code">
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]510static size_t StreamPixels(const Image *image,const void *pixels,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]511 const size_t columns)
512{
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]513 register const PixelPacket
514 *p;
515
516 MyData
517 *my_data;
518
519 my_data=(MyData *) image->client_data;
520 p=(PixelPacket *) pixels;
521 if (p != (const PixelPacket *) NULL)
522 {
523 /* process pixels here */
524 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]525 return(columns);
526}
527
528...
529/* invoke the pixel stream here */
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]530image_info->client_data=(void *) MyData;
531image=ReadStream(image_info,&amp;StreamPixels,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]532</pre>
533
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]534<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]535
536</div>
537
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]538<h2><a id="properties"></a>Image Properties and Profiles</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]539<div class="doc-section">
540
541<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>
542
543<pre class="code">
544 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
545</pre>
546
547<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>
548
549<pre class="code">
550 const char
551 *comment;
552
553 (void) SetImageProperty(image,"comment","This space for rent");
554 comment=GetImageProperty(image,"comment");
555 if (comment == (const char *) NULL)
556 (void) printf("Image comment: %s\n",comment);
557</pre>
558
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]559<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]560
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]561<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>
562
563<pre class="code">
564 StringInfo
565 *profile;
566
567 profile=AcquireStringInfo(length);
568 SetStringInfoDatum(profile,my_exif_profile);
569 (void) SetImageProfile(image,"EXIF",profile);
570 DestroyStringInfo(profile);
571 profile=GetImageProfile(image,"EXIF");
572 if (profile != (StringInfo *) NULL)
573 (void) PrintStringInfo(stdout,"EXIF",profile);
574</pre>
575
576</div>
577
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]578<h2><a id="tera-pixel"></a>Large Image Support</h2>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]579<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]580<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]581
582<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]583<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]584
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]585<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]586<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>
587
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]588<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]589<p>Here we force all image pixels to disk:</p>
590
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]591<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]592<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]593
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]594<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]595
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]596<h2><a id="threads"></a>Threads of Execution</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]597<div class="doc-section">
598
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]599<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]600
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]601<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]602
603<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]604{
605 CacheView
606 *image_view;
607
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]608 MagickBooleanType
609 status;
610
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]611 ssize_t
612 y;
613
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]614 status=MagickTrue;
615 image_view=AcquireCacheView(image);
616 #pragma omp parallel for schedule(dynamic,4) shared(status)
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]617 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]618 {
619 register IndexPacket
620 *indexes;
621
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]622 register PixelPacket
623 *q;
624
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]625 register ssize_t
626 x;
627
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]628 if (status == MagickFalse)
629 continue;
630 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
631 if (q == (PixelPacket *) NULL)
632 {
633 status=MagickFalse;
634 continue;
635 }
636 indexes=GetCacheViewAuthenticIndexQueue(image_view);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]637 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]638 {
639 q-&gt;red= ...
640 q-&gt;green= ...
641 q-&gt;blue= ...
642 q-&gt;opacity= ...
643 if (indexes != (IndexPacket *) NULL)
644 indexes[x]= ...
645 q++;
646 }
647 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
648 status=MagickFalse;
649 }
650 image_view=DestroyCacheView(image_view);
651 if (status == MagickFalse)
652 perror("something went wrong");
653}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]654</div>
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]655<p>This code snippet converts an uncompressed Windows bitmap to a Magick++ image:</p>
656<div class="viewport">
657#include "Magick++.h"
658#include &lt;assert.h&gt;
659#include "omp.h"
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]660
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]661void ConvertBMPToImage(const BITMAPINFOHEADER *bmp_info,
662 const unsigned char *restrict pixels,Magick::Image *image)
663{
664 /*
665 Prepare the image so that we can modify the pixels directly.
666 */
667 assert(bmp_info->biCompression == BI_RGB);
668 assert(bmp_info->biWidth == image->columns());
669 assert(abs(bmp_info->biHeight) == image->rows());
670 image->modifyImage();
671 if (bmp_info->biBitCount == 24)
672 image->type(MagickCore::TrueColorType);
673 else
674 image->type(MagickCore::TrueColorMatteType);
675 register unsigned int bytes_per_row=bmp_info->biWidth*bmp_info->biBitCount/8;
676 if (bytes_per_row % 4 != 0) {
677 bytes_per_row=bytes_per_row+(4-bytes_per_row % 4); // divisible by 4.
678 }
679 /*
680 Copy all pixel data, row by row.
681 */
682 #pragma omp parallel for
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]683 for (int y=0; y &lt; int(image->rows()); y++)
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]684 {
685 int row=(bmp_info->biHeight > 0) ? (image->rows()-y-1) : y;
686 register const unsigned char *restrict p=pixels+row*bytes_per_row;
687 register MagickCore::PixelPacket *restrict q=
688 image->setPixels(0,y,image->columns(),1);
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]689 for (int x=0; x &lt; int(image->columns()); x++)
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]690 {
691 q->blue=p[0];
692 q->green=p[1];
693 q->red=p[2];
694 if (bmp_info->biBitCount == 32) {
695 q->opacity=p[3];
696 }
697 q++;
698 p+=bmp_info->biBitCount/8;
699 }
700 image->syncPixels(); // sync pixels to pixel cache.
701 }
702 return;
703}
704</div>
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]705
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]706<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>
707
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]708<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]709
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]710<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]711
712<pre class="text">
713 &lt;policy domain="resource" name="thread" value="2"/>
714</pre>
715
716<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>
717
718<pre class="text">
719 export MAGICK_THREAD_LIMIT=12
720</pre>
721
722<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>
723
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]724</div>
725
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]726<h2><a id="distributed"></a>Heterogeneous Distributed Processing</h2>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]727<div class="doc-section">
728<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>
729
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]730<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]731
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]732<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
733<p>If so, run this command to realize a significant speed-up for image convolution:</p>
734
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]735<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]736<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
737
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]738<p>Here is an example OpenCL kernel that convolves an image:</p>
739
740<div class="viewport">
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]741static inline long ClampToCanvas(const long offset,const ulong range)
742{
743 if (offset &lt; 0L)
744 return(0L);
745 if (offset >= range)
746 return((long) (range-1L));
747 return(offset);
748}
749
750static inline CLQuantum ClampToQuantum(const double value)
751{
752 if (value &lt; 0.0)
753 return((CLQuantum) 0);
754 if (value >= (double) QuantumRange)
755 return((CLQuantum) QuantumRange);
756 return((CLQuantum) (value+0.5));
757}
758
759__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
760 const ulong width,const ulong height,__global CLPixelType *destination)
761{
762 const ulong columns = get_global_size(0);
763 const ulong rows = get_global_size(1);
764
765 const long x = get_global_id(0);
766 const long y = get_global_id(1);
767
768 const double scale = (1.0/QuantumRange);
769 const long mid_width = (width-1)/2;
770 const long mid_height = (height-1)/2;
771 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
772 double gamma = 0.0;
773 register ulong i = 0;
774
775 for (long v=(-mid_height); v &lt;= mid_height; v++)
776 {
777 for (long u=(-mid_width); u &lt;= mid_width; u++)
778 {
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]779 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,
780 columns);
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]781 const double alpha=scale*(QuantumRange-source[index].w);
782 sum.x+=alpha*filter[i]*source[index].x;
783 sum.y+=alpha*filter[i]*source[index].y;
784 sum.z+=alpha*filter[i]*source[index].z;
785 sum.w+=filter[i]*source[index].w;
786 gamma+=alpha*filter[i];
787 i++;
788 }
789 }
790
791 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
792 const ulong index=y*columns+x;
793 destination[index].x=ClampToQuantum(gamma*sum.x);
794 destination[index].y=ClampToQuantum(gamma*sum.y);
795 destination[index].z=ClampToQuantum(gamma*sum.z);
796 destination[index].w=ClampToQuantum(sum.w);
797};
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]798</div>
799
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]800<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]801
802</div>
803
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]804<h2><a id="coders"></a>Custom Image Coders</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]805<div class="doc-section">
806
807<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>
808
809<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>
810
811<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]812/*
813 Include declarations.
814*/
815#include "magick/studio.h"
816#include "magick/blob.h"
817#include "magick/blob-private.h"
818#include "magick/colorspace.h"
819#include "magick/exception.h"
820#include "magick/exception-private.h"
821#include "magick/image.h"
822#include "magick/image-private.h"
823#include "magick/list.h"
824#include "magick/magick.h"
825#include "magick/memory_.h"
826#include "magick/monitor.h"
827#include "magick/monitor-private.h"
828#include "magick/quantum-private.h"
829#include "magick/static.h"
830#include "magick/string_.h"
831#include "magick/module.h"
832
833/*
834 Forward declarations.
835*/
836static MagickBooleanType
837 WriteMGKImage(const ImageInfo *,Image *);
838
839/*
840%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
841% %
842% %
843% %
844% I s M G K %
845% %
846% %
847% %
848%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
849%
850% IsMGK() returns MagickTrue if the image format type, identified by the
851% magick string, is MGK.
852%
853% The format of the IsMGK method is:
854%
855% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
856%
857% A description of each parameter follows:
858%
859% o magick: This string is generally the first few bytes of an image file
860% or blob.
861%
862% o length: Specifies the length of the magick string.
863%
864*/
865static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
866{
867 if (length &lt; 7)
868 return(MagickFalse);
869 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
870 return(MagickTrue);
871 return(MagickFalse);
872}
873
874/*
875%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
876% %
877% %
878% %
879% R e a d M G K I m a g e %
880% %
881% %
882% %
883%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
884%
885% ReadMGKImage() reads a MGK image file and returns it. It allocates
886% the memory necessary for the new Image structure and returns a pointer to
887% the new image.
888%
889% The format of the ReadMGKImage method is:
890%
891% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
892%
893% A description of each parameter follows:
894%
895% o image_info: the image info.
896%
897% o exception: return any errors or warnings in this structure.
898%
899*/
900static Image *ReadMGKImage(const ImageInfo *image_info,
901 ExceptionInfo *exception)
902{
903 char
904 buffer[MaxTextExtent];
905
906 Image
907 *image;
908
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]909 MagickBooleanType
910 status;
911
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]912 register PixelPacket
913 *q;
914
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]915 register size_t
916 x;
917
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]918 register unsigned char
919 *p;
920
921 ssize_t
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]922 count,
923 y;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]924
925 unsigned char
926 *pixels;
927
928 unsigned long
929 columns,
930 rows;
931
932 /*
933 Open image file.
934 */
935 assert(image_info != (const ImageInfo *) NULL);
936 assert(image_info-&gt;signature == MagickSignature);
937 if (image_info-&gt;debug != MagickFalse)
938 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
939 assert(exception != (ExceptionInfo *) NULL);
940 assert(exception-&gt;signature == MagickSignature);
941 image=AcquireImage(image_info);
942 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
943 if (status == MagickFalse)
944 {
945 image=DestroyImageList(image);
946 return((Image *) NULL);
947 }
948 /*
949 Read MGK image.
950 */
951 (void) ReadBlobString(image,buffer); /* read magic number */
952 if (IsMGK(buffer,7) == MagickFalse)
953 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
954 (void) ReadBlobString(image,buffer);
955 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
956 if (count &lt;= 0)
957 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
958 do
959 {
960 /*
961 Initialize image structure.
962 */
963 image-&gt;columns=columns;
964 image-&gt;rows=rows;
965 image-&gt;depth=8;
966 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
967 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
968 break;
969 /*
970 Convert MGK raster image to pixel packets.
971 */
972 if (SetImageExtent(image,0,0) == MagickFalse)
973 {
974 InheritException(exception,&amp;image-&gt;exception);
975 return(DestroyImageList(image));
976 }
977 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
978 if (pixels == (unsigned char *) NULL)
979 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]980 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]981 {
982 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
983 if (count != (ssize_t) (3*image-&gt;columns))
984 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
985 p=pixels;
986 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
987 if (q == (PixelPacket *) NULL)
988 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]989 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]990 {
991 q-&gt;red=ScaleCharToQuantum(*p++);
992 q-&gt;green=ScaleCharToQuantum(*p++);
993 q-&gt;blue=ScaleCharToQuantum(*p++);
994 q++;
995 }
996 if (SyncAuthenticPixels(image,exception) == MagickFalse)
997 break;
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]998 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]999 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
1000 break;
1001 }
1002 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1003 if (EOFBlob(image) != MagickFalse)
1004 {
1005 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
1006 break;
1007 }
1008 /*
1009 Proceed to next image.
1010 */
1011 if (image_info-&gt;number_scenes != 0)
1012 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
1013 break;
1014 *buffer='\0';
1015 (void) ReadBlobString(image,buffer);
1016 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
1017 if (count != 0)
1018 {
1019 /*
1020 Allocate next image structure.
1021 */
1022 AcquireNextImage(image_info,image);
1023 if (GetNextImageInList(image) == (Image *) NULL)
1024 {
1025 image=DestroyImageList(image);
1026 return((Image *) NULL);
1027 }
1028 image=SyncNextImageInList(image);
1029 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
1030 if (status == MagickFalse)
1031 break;
1032 }
1033 } while (count != 0);
1034 (void) CloseBlob(image);
1035 return(GetFirstImageInList(image));
1036}
1037
1038/*
1039%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1040% %
1041% %
1042% %
1043% R e g i s t e r M G K I m a g e %
1044% %
1045% %
1046% %
1047%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1048%
1049% RegisterMGKImage() adds attributes for the MGK image format to
1050% the list of supported formats. The attributes include the image format
1051% tag, a method to read and/or write the format, whether the format
1052% supports the saving of more than one frame to the same file or blob,
1053% whether the format supports native in-memory I/O, and a brief
1054% description of the format.
1055%
1056% The format of the RegisterMGKImage method is:
1057%
1058% unsigned long RegisterMGKImage(void)
1059%
1060*/
1061ModuleExport unsigned long RegisterMGKImage(void)
1062{
1063 MagickInfo
1064 *entry;
1065
1066 entry=SetMagickInfo("MGK");
1067 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
1068 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
1069 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
1070 entry-&gt;description=ConstantString("MGK");
1071 entry-&gt;module=ConstantString("MGK");
1072 (void) RegisterMagickInfo(entry);
1073 return(MagickImageCoderSignature);
1074}
1075
1076/*
1077%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1078% %
1079% %
1080% %
1081% U n r e g i s t e r M G K I m a g e %
1082% %
1083% %
1084% %
1085%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1086%
1087% UnregisterMGKImage() removes format registrations made by the
1088% MGK module from the list of supported formats.
1089%
1090% The format of the UnregisterMGKImage method is:
1091%
1092% UnregisterMGKImage(void)
1093%
1094*/
1095ModuleExport void UnregisterMGKImage(void)
1096{
1097 (void) UnregisterMagickInfo("MGK");
1098}
1099
1100/*
1101%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1102% %
1103% %
1104% %
1105% W r i t e M G K I m a g e %
1106% %
1107% %
1108% %
1109%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1110%
1111% WriteMGKImage() writes an image to a file in red, green, and blue
1112% MGK rasterfile format.
1113%
1114% The format of the WriteMGKImage method is:
1115%
1116% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1117%
1118% A description of each parameter follows.
1119%
1120% o image_info: the image info.
1121%
1122% o image: The image.
1123%
1124*/
1125static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1126{
1127 char
1128 buffer[MaxTextExtent];
1129
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1130 MagickBooleanType
1131 status;
1132
1133 MagickOffsetType
1134 scene;
1135
1136 register const PixelPacket
1137 *p;
1138
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1139 register ssize_t
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1140 x;
1141
1142 register unsigned char
1143 *q;
1144
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1145 ssize_t
1146 y;
1147
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1148 unsigned char
1149 *pixels;
1150
1151 /*
1152 Open output image file.
1153 */
1154 assert(image_info != (const ImageInfo *) NULL);
1155 assert(image_info-&gt;signature == MagickSignature);
1156 assert(image != (Image *) NULL);
1157 assert(image-&gt;signature == MagickSignature);
1158 if (image-&gt;debug != MagickFalse)
1159 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1160 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1161 if (status == MagickFalse)
1162 return(status);
1163 scene=0;
1164 do
1165 {
1166 /*
1167 Allocate memory for pixels.
1168 */
1169 if (image-&gt;colorspace != RGBColorspace)
1170 (void) SetImageColorspace(image,RGBColorspace);
1171 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1172 3UL*sizeof(*pixels));
1173 if (pixels == (unsigned char *) NULL)
1174 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1175 /*
1176 Initialize raster file header.
1177 */
1178 (void) WriteBlobString(image,"id=mgk\n");
1179 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1180 image-&gt;columns,image-&gt;rows);
1181 (void) WriteBlobString(image,buffer);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1182 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1183 {
1184 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1185 if (p == (const PixelPacket *) NULL)
1186 break;
1187 q=pixels;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1188 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1189 {
1190 *q++=ScaleQuantumToChar(p-&gt;red);
1191 *q++=ScaleQuantumToChar(p-&gt;green);
1192 *q++=ScaleQuantumToChar(p-&gt;blue);
1193 p++;
1194 }
1195 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1196 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1197 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1198 break;
1199 }
1200 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1201 if (GetNextImageInList(image) == (Image *) NULL)
1202 break;
1203 image=SyncNextImageInList(image);
1204 status=SetImageProgress(image,SaveImagesTag,scene,
1205 GetImageListLength(image));
1206 if (status == MagickFalse)
1207 break;
1208 scene++;
1209 } while (image_info-&gt;adjoin != MagickFalse);
1210 (void) CloseBlob(image);
1211 return(MagickTrue);
1212}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1213</div>
1214
1215<p>To invoke the custom coder from the command line, use these commands:</p>
1216
1217<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>
1218<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>
1219
1220</div>
1221
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1222<h2><a id="filters"></a>Custom Image Filters</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1223<div class="doc-section">
1224
1225<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>
1226
1227<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>
1228
1229<div class="viewport">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1230#include &lt;stdio.h&gt;
1231#include &lt;stdlib.h&gt;
1232#include &lt;string.h&gt;
1233#include &lt;time.h&gt;
1234#include &lt;assert.h&gt;
1235#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1236#include "magick/MagickCore.h"
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1237
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1238/*
1239%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1240% %
1241% %
1242% %
1243% a n a l y z e I m a g e %
1244% %
1245% %
1246% %
1247%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1248%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1249% analyzeImage() computes the brightness and saturation mean, standard
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]1250% deviation, kurtosis and skewness and stores these values as attributes
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1251% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1252%
1253% The format of the analyzeImage method is:
1254%
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1255% size_t analyzeImage(Image *images,const int argc,char **argv,
1256% ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1257%
1258% A description of each parameter follows:
1259%
1260% o image: the address of a structure of type Image.
1261%
1262% o argc: Specifies a pointer to an integer describing the number of
1263% elements in the argument vector.
1264%
1265% o argv: Specifies a pointer to a text array containing the command line
1266% arguments.
1267%
1268% o exception: return any errors or warnings in this structure.
1269%
1270*/
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1271ModuleExport size_t analyzeImage(Image **images,const int argc,const char **argv,
1272 ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1273{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1274 char
1275 text[MaxTextExtent];
1276
1277 double
1278 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1279 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1280 brightness_mean,
1281 brightness_standard_deviation,
1282 brightness_kurtosis,
1283 brightness_skewness,
1284 brightness_sum_x,
1285 brightness_sum_x2,
1286 brightness_sum_x3,
1287 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1288 hue,
1289 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1290 saturation_mean,
1291 saturation_standard_deviation,
1292 saturation_kurtosis,
1293 saturation_skewness,
1294 saturation_sum_x,
1295 saturation_sum_x2,
1296 saturation_sum_x3,
1297 saturation_sum_x4;
1298
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1299 Image
1300 *image;
1301
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1302 assert(images != (Image **) NULL);
1303 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1304 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1305 (void) argc;
1306 (void) argv;
1307 image=(*images);
1308 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1309 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1310 CacheView
1311 *image_view;
1312
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1313 MagickBooleanType
1314 status;
1315
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1316 ssize_t
1317 y;
1318
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1319 brightness_sum_x=0.0;
1320 brightness_sum_x2=0.0;
1321 brightness_sum_x3=0.0;
1322 brightness_sum_x4=0.0;
1323 brightness_mean=0.0;
1324 brightness_standard_deviation=0.0;
1325 brightness_kurtosis=0.0;
1326 brightness_skewness=0.0;
1327 saturation_sum_x=0.0;
1328 saturation_sum_x2=0.0;
1329 saturation_sum_x3=0.0;
1330 saturation_sum_x4=0.0;
1331 saturation_mean=0.0;
1332 saturation_standard_deviation=0.0;
1333 saturation_kurtosis=0.0;
1334 saturation_skewness=0.0;
1335 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1336 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1337 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1338#if defined(MAGICKCORE_OPENMP_SUPPORT)
1339 #pragma omp parallel for schedule(dynamic,4) shared(status)
1340#endif
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1341 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1342 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1343 register const PixelPacket
1344 *p;
1345
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1346 register ssize_t
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1347 x;
1348
1349 if (status == MagickFalse)
1350 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1351 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1352 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1353 {
1354 status=MagickFalse;
1355 continue;
1356 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1357 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1358 {
1359 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1360 brightness*=QuantumRange;
1361 brightness_sum_x+=brightness;
1362 brightness_sum_x2+=brightness*brightness;
1363 brightness_sum_x3+=brightness*brightness*brightness;
1364 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1365 saturation*=QuantumRange;
1366 saturation_sum_x+=saturation;
1367 saturation_sum_x2+=saturation*saturation;
1368 saturation_sum_x3+=saturation*saturation*saturation;
1369 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1370 area++;
1371 p++;
1372 }
1373 }
1374 image_view=DestroyCacheView(image_view);
1375 if (area &lt;= 0.0)
1376 break;
1377 brightness_mean=brightness_sum_x/area;
1378 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1379 (void) SetImageProperty(image,"filter:brightness:mean",text);
1380 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1381 area*brightness_sum_x/area));
1382 (void) FormatMagickString(text,MaxTextExtent,"%g",
1383 brightness_standard_deviation);
1384 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1385 if (brightness_standard_deviation != 0)
1386 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1387 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1388 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1389 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1390 brightness_standard_deviation*brightness_standard_deviation*
1391 brightness_standard_deviation)-3.0;
1392 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1393 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1394 if (brightness_standard_deviation != 0)
1395 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1396 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1397 brightness_mean)/(brightness_standard_deviation*
1398 brightness_standard_deviation*brightness_standard_deviation);
1399 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1400 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1401 saturation_mean=saturation_sum_x/area;
1402 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1403 (void) SetImageProperty(image,"filter:saturation:mean",text);
1404 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1405 area*saturation_sum_x/area));
1406 (void) FormatMagickString(text,MaxTextExtent,"%g",
1407 saturation_standard_deviation);
1408 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1409 if (saturation_standard_deviation != 0)
1410 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1411 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1412 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1413 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1414 saturation_standard_deviation*saturation_standard_deviation*
1415 saturation_standard_deviation)-3.0;
1416 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1417 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1418 if (saturation_standard_deviation != 0)
1419 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1420 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1421 saturation_mean)/(saturation_standard_deviation*
1422 saturation_standard_deviation*saturation_standard_deviation);
1423 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1424 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1425 }
1426 return(MagickImageFilterSignature);
1427}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1428</div>
1429
1430<p>To invoke the custom filter from the command line, use this command:</p>
1431
1432<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/>
1433 Format: LOGO (ImageMagick Logo) <br/>
1434 Class: PseudoClass <br/>
1435 Geometry: 640x480 <br/>
1436 ... <br/>
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1437 filter:brightness:kurtosis: 8.17947 <br/>
1438 filter:brightness:mean: 60632.1 <br/>
1439 filter:brightness:skewness: -2.97118 <br/>
1440 filter:brightness:standard-deviation: 13742.1 <br/>
1441 filter:saturation:kurtosis: 4.33554 <br/>
1442 filter:saturation:mean: 5951.55 <br/>
1443 filter:saturation:skewness: 2.42848 <br/>
1444 filter:saturation:standard-deviation: 15575.9</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1445
1446<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>
1447
1448</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1449
1450</div>
1451
1452<div id="linkbar">
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1458 <span id="linkbar-east">&nbsp;</span>
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1460 <div class="footer">
cristy7e41fe82010-12-04 23:12:08 +0000[diff] [blame]1461 <span id="footer-west">&copy; 1999-2011 ImageMagick Studio LLC</span>
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1463 </div>
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