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200<div class="main">
201
202
203
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]204<h1>The <em>Magick</em> Behind ImageMagick</h1>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]205<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]206
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]207
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]208<div class="doc-section">
209<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>
210</div>
211
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]212<h2><a id="overview"></a>Architecture Overview</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]213<div class="doc-section">
214
215<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>
216
217<ul>
218 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
219 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
220 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
221 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
222 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
223 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
224</ul>
225
226<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>
227
228<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
229
230<ul>
231 <li>one pixel a time (e.g. pixel at location 10,3)</li>
232 <li>a single scanline (e.g. all pixels from row 4)</li>
233 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
234 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
235 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
236 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
237 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
238 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
239 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
240 <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>
241 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]242 <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]243</ul>
244
245<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>
246
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]247<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]248
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]249<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]250
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]251<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]252
253</div>
254
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]255<h2><a id="cache"></a>The Pixel Cache</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]256<div class="doc-section">
257
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]258<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]259
260<h3>Create the Pixel Cache</h3>
261<div class="doc-section">
262
263<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>
264
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]265<dl>
266<dt>Create an image canvas initialized to the background color:</dt>
267<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]268 image=AllocateImage(image_info);
269 if (SetImageExtent(image,640,480) == MagickFalse)
270 { /* an exception was thrown */ }
271 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
272 SetImageBackgroundColor(image);
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]273</p></dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]274
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]275<dt>Create an image from a JPEG image on disk:</dt>
276<dd><p class="code">
277 (void) strcpy(image_info-&gt;filename,"image.jpg"):
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]278 image=ReadImage(image_info,exception);
279 if (image == (Image *) NULL)
280 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]281</p></dd>
282<dt>Create an image from a memory based image:</dt>
283<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]284 image=BlobToImage(blob_info,blob,extent,exception);
285 if (image == (Image *) NULL)
286 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]287</p></dd>
288</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]289
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]290<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]291
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]292<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]293
cristy4bf6e232011-05-21 01:43:33 +0000[diff] [blame^]294<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.9-10 2011-04-06 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]295<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]296</div>
297
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]298<h3><a id="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]299<div class="doc-section">
300
301<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]302<ul>
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]303 <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]304 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
305 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
306 <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]307</ul>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]308
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]309<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]310
311<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]312 const PixelPacket
313 *p;
314
315 PixelPacket
316 *q;
317
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]318 ssize_t
319 x,
320 y;
321
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]322 destination=CloneImage(source,source->columns,source->rows,MagickTrue,
323 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]324 if (destination == (Image *) NULL)
325 { /* an exception was thrown */ }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]326 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]327 {
328 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
329 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
330 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
331 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]332 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]333 {
334 q-&gt;red=90*p-&gt;red/100;
335 q-&gt;green=90*p-&gt;green/100;
336 q-&gt;blue=90*p-&gt;blue/100;
337 q-&gt;opacity=90*p-&gt;opacity/100;
338 p++;
339 q++;
340 }
341 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
342 break;
343 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]344 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]345 { /* an exception was thrown */ }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]346</div>
347
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]348<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]349
350<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>
351
352<pre class="code">
353 const IndexPacket
354 *indexes;
355
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]356 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]357 {
358 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
359 if (p == (const PixelPacket *) NULL)
360 break;
361 indexes=GetVirtualIndexes(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]362 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]363 (void) printf("%d\n",GetIndexPixelComponent(indexes+x));
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]364 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]365 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]366 /* an exception was thrown */
367</pre>
368
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]369<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]370
371<pre class="code">
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]372 p=GetVirtualPixels(source,-3,-3,source-&gt;columns+3,6,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]373</pre>
374
375<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
376</div>
377
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]378<h3><a id="virtual-pixels"></a>Virtual Pixels</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]379<div class="doc-section">
380
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]381<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]382 <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>
383
cristy4c54bbb2011-03-17 13:53:13 +0000[diff] [blame]384<pre class="text" style="font-size: 83.3333%;">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]385 background: the area surrounding the image is the background color
386 black: the area surrounding the image is black
387 checker-tile: alternate squares with image and background color
388 dither: non-random 32x32 dithered pattern
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]389 edge: extend the edge pixel toward infinity (default)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]390 gray: the area surrounding the image is gray
391 horizontal-tile: horizontally tile the image, background color above/below
392 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
393 mirror: mirror tile the image
394 random: choose a random pixel from the image
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]395 tile: tile the image
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]396 transparent: the area surrounding the image is transparent blackness
397 vertical-tile: vertically tile the image, sides are background color
398 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
399 white: the area surrounding the image is white
400</pre>
401
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]402</div>
403
404<h3>Cache Storage and Resource Requirements</h3>
405<div class="doc-section">
406
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]407<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]408
409<dl class="doc">
410 <dt class="doc">files</dt>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]411 <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]412 <dt class="doc">area</dt>
413 <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>
414 <dt class="doc">memory</dt>
415 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
416 <dt class="doc">map</dt>
417 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
418 <dt class="doc">disk</dt>
419 <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]420 <dt class="doc">thread</dt>
421 <dd>maximum number of threads that are permitted to run in parallel.</dd>
422 <dt class="doc">time</dt>
423 <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]424</dl>
425
426<p>To determine the current setting of these limits, use this command:</p>
427
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]428<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span></p><pre class="text">
429File Area Memory Map Disk Thread Time
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]430-------------------------------------------------------------------------------
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]431 768 1.0386GB 3.8692GiB 7.7384GiB unlimited 4 unlimited
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]432</pre>
433
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]434<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]435
436<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>
437</div>
438
439<h3>Cache Views</h3>
440<div class="doc-section">
441
442<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>
443
444<pre class="code">
445 CacheView
446 *view_1,
447 *view_2;
448
cristye9a32c32011-04-07 01:11:05 +0000[diff] [blame]449 view_1=AcquireCacheView(source);
450 view_2=AcquireCacheView(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]451 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]452 {
453 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]454 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,
455 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]456 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
457 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]458 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]459 {
460 /* do something with u &amp; v here */
461 }
462 }
cristye9a32c32011-04-07 01:11:05 +0000[diff] [blame]463 view_2=DestroyCacheView(view_2);
464 view_1=DestroyCacheView(view_1);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]465 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]466 { /* an exception was thrown */ }
467</pre>
468</div>
469
470<h3>Magick Persistent Cache Format</h3>
471<div class="doc-section">
472
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]473<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]474<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]475</div>
476
477<h3>Best Practices</h3>
478<div class="doc-section">
479
cristy30092792011-02-22 02:06:14 +0000[diff] [blame]480<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]481
482<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>
483
484<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>
485
486<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>
487
488<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>
489
490<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>
491
492<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>
493
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]494<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]495
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]496<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]497
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]498<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]499
500<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>
501
502<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>
503<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>
504</div>
505
506</div>
507
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]508<h2><a id="stream"></a>Streaming Pixels</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]509<div class="doc-section">
510
511<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>
512
513<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>
514
515<pre class="code">
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]516static size_t StreamPixels(const Image *image,const void *pixels,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]517 const size_t columns)
518{
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]519 register const PixelPacket
520 *p;
521
522 MyData
523 *my_data;
524
525 my_data=(MyData *) image->client_data;
526 p=(PixelPacket *) pixels;
527 if (p != (const PixelPacket *) NULL)
528 {
529 /* process pixels here */
530 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]531 return(columns);
532}
533
534...
535/* invoke the pixel stream here */
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]536image_info->client_data=(void *) MyData;
537image=ReadStream(image_info,&amp;StreamPixels,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]538</pre>
539
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]540<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]541
542</div>
543
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]544<h2><a id="properties"></a>Image Properties and Profiles</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]545<div class="doc-section">
546
547<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>
548
549<pre class="code">
550 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
551</pre>
552
553<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>
554
555<pre class="code">
556 const char
557 *comment;
558
559 (void) SetImageProperty(image,"comment","This space for rent");
560 comment=GetImageProperty(image,"comment");
561 if (comment == (const char *) NULL)
562 (void) printf("Image comment: %s\n",comment);
563</pre>
564
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]565<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]566
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]567<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>
568
569<pre class="code">
570 StringInfo
571 *profile;
572
573 profile=AcquireStringInfo(length);
574 SetStringInfoDatum(profile,my_exif_profile);
575 (void) SetImageProfile(image,"EXIF",profile);
576 DestroyStringInfo(profile);
577 profile=GetImageProfile(image,"EXIF");
578 if (profile != (StringInfo *) NULL)
579 (void) PrintStringInfo(stdout,"EXIF",profile);
580</pre>
581
582</div>
583
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]584<h2><a id="tera-pixel"></a>Large Image Support</h2>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]585<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]586<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]587
588<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]589<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]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 logo: \ <br/> -resize 250000x250000 logo.miff</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]592<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>
593
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]594<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]595<p>Here we force all image pixels to disk:</p>
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 -limit area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
cristybac7a162010-06-15 19:57:29 +0000[diff] [blame]598<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]599
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]600<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]601
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]602<h2><a id="threads"></a>Threads of Execution</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]603<div class="doc-section">
604
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]605<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]606
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]607<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]608
609<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]610{
611 CacheView
612 *image_view;
613
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]614 MagickBooleanType
615 status;
616
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]617 ssize_t
618 y;
619
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]620 status=MagickTrue;
621 image_view=AcquireCacheView(image);
622 #pragma omp parallel for schedule(dynamic,4) shared(status)
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]623 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]624 {
625 register IndexPacket
626 *indexes;
627
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]628 register PixelPacket
629 *q;
630
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]631 register ssize_t
632 x;
633
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]634 if (status == MagickFalse)
635 continue;
636 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
637 if (q == (PixelPacket *) NULL)
638 {
639 status=MagickFalse;
640 continue;
641 }
642 indexes=GetCacheViewAuthenticIndexQueue(image_view);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]643 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]644 {
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]645 SetRedPixelComponent(q,...);
646 SetGreenPixelComponent(q,...);
647 SetBluePixelComponent(q,...);
648 SetOpacityPixelComponent(q,...);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]649 if (indexes != (IndexPacket *) NULL)
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]650 SetIndexPixelComponent(indexes+x,...);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]651 q++;
652 }
653 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
654 status=MagickFalse;
655 }
656 image_view=DestroyCacheView(image_view);
657 if (status == MagickFalse)
658 perror("something went wrong");
659}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]660</div>
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]661<p>This code snippet converts an uncompressed Windows bitmap to a Magick++ image:</p>
662<div class="viewport">
663#include "Magick++.h"
664#include &lt;assert.h&gt;
665#include "omp.h"
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]666
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]667void ConvertBMPToImage(const BITMAPINFOHEADER *bmp_info,
668 const unsigned char *restrict pixels,Magick::Image *image)
669{
670 /*
671 Prepare the image so that we can modify the pixels directly.
672 */
673 assert(bmp_info->biCompression == BI_RGB);
674 assert(bmp_info->biWidth == image->columns());
675 assert(abs(bmp_info->biHeight) == image->rows());
676 image->modifyImage();
677 if (bmp_info->biBitCount == 24)
678 image->type(MagickCore::TrueColorType);
679 else
680 image->type(MagickCore::TrueColorMatteType);
681 register unsigned int bytes_per_row=bmp_info->biWidth*bmp_info->biBitCount/8;
682 if (bytes_per_row % 4 != 0) {
683 bytes_per_row=bytes_per_row+(4-bytes_per_row % 4); // divisible by 4.
684 }
685 /*
686 Copy all pixel data, row by row.
687 */
688 #pragma omp parallel for
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]689 for (int y=0; y &lt; int(image->rows()); y++)
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]690 {
691 int row=(bmp_info->biHeight > 0) ? (image->rows()-y-1) : y;
692 register const unsigned char *restrict p=pixels+row*bytes_per_row;
693 register MagickCore::PixelPacket *restrict q=
694 image->setPixels(0,y,image->columns(),1);
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]695 for (int x=0; x &lt; int(image->columns()); x++)
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]696 {
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]697 SetBluePixelComponent(q,p[0]);
698 SetGreenPixelComponent(q,p[1]);
699 SetRedPixelComponent(q,p[2]);
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]700 if (bmp_info->biBitCount == 32) {
cristyacc04882011-05-04 23:03:43 +0000[diff] [blame]701 SetOpacityPixelComponent(q,p[3]);
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]702 }
703 q++;
704 p+=bmp_info->biBitCount/8;
705 }
706 image->syncPixels(); // sync pixels to pixel cache.
707 }
708 return;
709}
710</div>
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]711
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]712<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>
713
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]714<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]715
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]716<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]717
718<pre class="text">
719 &lt;policy domain="resource" name="thread" value="2"/>
720</pre>
721
722<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>
723
724<pre class="text">
725 export MAGICK_THREAD_LIMIT=12
726</pre>
727
728<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>
729
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]730</div>
731
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]732<h2><a id="distributed"></a>Heterogeneous Distributed Processing</h2>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]733<div class="doc-section">
734<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>
735
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]736<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]737
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]738<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
739<p>If so, run this command to realize a significant speed-up for image convolution:</p>
740
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]741<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]742<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
743
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]744<p>Here is an example OpenCL kernel that convolves an image:</p>
745
746<div class="viewport">
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]747static inline long ClampToCanvas(const long offset,const ulong range)
748{
749 if (offset &lt; 0L)
750 return(0L);
751 if (offset >= range)
752 return((long) (range-1L));
753 return(offset);
754}
755
756static inline CLQuantum ClampToQuantum(const double value)
757{
758 if (value &lt; 0.0)
759 return((CLQuantum) 0);
760 if (value >= (double) QuantumRange)
761 return((CLQuantum) QuantumRange);
762 return((CLQuantum) (value+0.5));
763}
764
765__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
766 const ulong width,const ulong height,__global CLPixelType *destination)
767{
768 const ulong columns = get_global_size(0);
769 const ulong rows = get_global_size(1);
770
771 const long x = get_global_id(0);
772 const long y = get_global_id(1);
773
774 const double scale = (1.0/QuantumRange);
775 const long mid_width = (width-1)/2;
776 const long mid_height = (height-1)/2;
777 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
778 double gamma = 0.0;
779 register ulong i = 0;
780
781 for (long v=(-mid_height); v &lt;= mid_height; v++)
782 {
783 for (long u=(-mid_width); u &lt;= mid_width; u++)
784 {
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]785 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,
786 columns);
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]787 const double alpha=scale*(QuantumRange-source[index].w);
788 sum.x+=alpha*filter[i]*source[index].x;
789 sum.y+=alpha*filter[i]*source[index].y;
790 sum.z+=alpha*filter[i]*source[index].z;
791 sum.w+=filter[i]*source[index].w;
792 gamma+=alpha*filter[i];
793 i++;
794 }
795 }
796
797 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
798 const ulong index=y*columns+x;
799 destination[index].x=ClampToQuantum(gamma*sum.x);
800 destination[index].y=ClampToQuantum(gamma*sum.y);
801 destination[index].z=ClampToQuantum(gamma*sum.z);
802 destination[index].w=ClampToQuantum(sum.w);
803};
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]804</div>
805
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]806<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]807
808</div>
809
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]810<h2><a id="coders"></a>Custom Image Coders</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]811<div class="doc-section">
812
813<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>
814
815<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>
816
817<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]818/*
819 Include declarations.
820*/
821#include "magick/studio.h"
822#include "magick/blob.h"
823#include "magick/blob-private.h"
824#include "magick/colorspace.h"
825#include "magick/exception.h"
826#include "magick/exception-private.h"
827#include "magick/image.h"
828#include "magick/image-private.h"
829#include "magick/list.h"
830#include "magick/magick.h"
831#include "magick/memory_.h"
832#include "magick/monitor.h"
833#include "magick/monitor-private.h"
834#include "magick/quantum-private.h"
835#include "magick/static.h"
836#include "magick/string_.h"
837#include "magick/module.h"
838
839/*
840 Forward declarations.
841*/
842static MagickBooleanType
843 WriteMGKImage(const ImageInfo *,Image *);
844
845/*
846%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
847% %
848% %
849% %
850% I s M G K %
851% %
852% %
853% %
854%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
855%
856% IsMGK() returns MagickTrue if the image format type, identified by the
857% magick string, is MGK.
858%
859% The format of the IsMGK method is:
860%
861% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
862%
863% A description of each parameter follows:
864%
865% o magick: This string is generally the first few bytes of an image file
866% or blob.
867%
868% o length: Specifies the length of the magick string.
869%
870*/
871static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
872{
873 if (length &lt; 7)
874 return(MagickFalse);
875 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
876 return(MagickTrue);
877 return(MagickFalse);
878}
879
880/*
881%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
882% %
883% %
884% %
885% R e a d M G K I m a g e %
886% %
887% %
888% %
889%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
890%
891% ReadMGKImage() reads a MGK image file and returns it. It allocates
892% the memory necessary for the new Image structure and returns a pointer to
893% the new image.
894%
895% The format of the ReadMGKImage method is:
896%
897% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
898%
899% A description of each parameter follows:
900%
901% o image_info: the image info.
902%
903% o exception: return any errors or warnings in this structure.
904%
905*/
906static Image *ReadMGKImage(const ImageInfo *image_info,
907 ExceptionInfo *exception)
908{
909 char
910 buffer[MaxTextExtent];
911
912 Image
913 *image;
914
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]915 MagickBooleanType
916 status;
917
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]918 register PixelPacket
919 *q;
920
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]921 register size_t
922 x;
923
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]924 register unsigned char
925 *p;
926
927 ssize_t
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]928 count,
929 y;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]930
931 unsigned char
932 *pixels;
933
934 unsigned long
935 columns,
936 rows;
937
938 /*
939 Open image file.
940 */
941 assert(image_info != (const ImageInfo *) NULL);
942 assert(image_info-&gt;signature == MagickSignature);
943 if (image_info-&gt;debug != MagickFalse)
944 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
945 assert(exception != (ExceptionInfo *) NULL);
946 assert(exception-&gt;signature == MagickSignature);
947 image=AcquireImage(image_info);
948 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
949 if (status == MagickFalse)
950 {
951 image=DestroyImageList(image);
952 return((Image *) NULL);
953 }
954 /*
955 Read MGK image.
956 */
957 (void) ReadBlobString(image,buffer); /* read magic number */
958 if (IsMGK(buffer,7) == MagickFalse)
959 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
960 (void) ReadBlobString(image,buffer);
961 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
962 if (count &lt;= 0)
963 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
964 do
965 {
966 /*
967 Initialize image structure.
968 */
969 image-&gt;columns=columns;
970 image-&gt;rows=rows;
971 image-&gt;depth=8;
972 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
973 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
974 break;
975 /*
976 Convert MGK raster image to pixel packets.
977 */
978 if (SetImageExtent(image,0,0) == MagickFalse)
979 {
980 InheritException(exception,&amp;image-&gt;exception);
981 return(DestroyImageList(image));
982 }
983 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
984 if (pixels == (unsigned char *) NULL)
985 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]986 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]987 {
988 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
989 if (count != (ssize_t) (3*image-&gt;columns))
990 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
991 p=pixels;
992 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
993 if (q == (PixelPacket *) NULL)
994 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]995 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]996 {
997 q-&gt;red=ScaleCharToQuantum(*p++);
998 q-&gt;green=ScaleCharToQuantum(*p++);
999 q-&gt;blue=ScaleCharToQuantum(*p++);
1000 q++;
1001 }
1002 if (SyncAuthenticPixels(image,exception) == MagickFalse)
1003 break;
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1004 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1005 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
1006 break;
1007 }
1008 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1009 if (EOFBlob(image) != MagickFalse)
1010 {
1011 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
1012 break;
1013 }
1014 /*
1015 Proceed to next image.
1016 */
1017 if (image_info-&gt;number_scenes != 0)
1018 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
1019 break;
1020 *buffer='\0';
1021 (void) ReadBlobString(image,buffer);
1022 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
1023 if (count != 0)
1024 {
1025 /*
1026 Allocate next image structure.
1027 */
1028 AcquireNextImage(image_info,image);
1029 if (GetNextImageInList(image) == (Image *) NULL)
1030 {
1031 image=DestroyImageList(image);
1032 return((Image *) NULL);
1033 }
1034 image=SyncNextImageInList(image);
1035 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
1036 if (status == MagickFalse)
1037 break;
1038 }
1039 } while (count != 0);
1040 (void) CloseBlob(image);
1041 return(GetFirstImageInList(image));
1042}
1043
1044/*
1045%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1046% %
1047% %
1048% %
1049% R e g i s t e r M G K I m a g e %
1050% %
1051% %
1052% %
1053%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1054%
1055% RegisterMGKImage() adds attributes for the MGK image format to
1056% the list of supported formats. The attributes include the image format
1057% tag, a method to read and/or write the format, whether the format
1058% supports the saving of more than one frame to the same file or blob,
1059% whether the format supports native in-memory I/O, and a brief
1060% description of the format.
1061%
1062% The format of the RegisterMGKImage method is:
1063%
1064% unsigned long RegisterMGKImage(void)
1065%
1066*/
1067ModuleExport unsigned long RegisterMGKImage(void)
1068{
1069 MagickInfo
1070 *entry;
1071
1072 entry=SetMagickInfo("MGK");
1073 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
1074 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
1075 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
1076 entry-&gt;description=ConstantString("MGK");
1077 entry-&gt;module=ConstantString("MGK");
1078 (void) RegisterMagickInfo(entry);
1079 return(MagickImageCoderSignature);
1080}
1081
1082/*
1083%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1084% %
1085% %
1086% %
1087% U n r e g i s t e r M G K I m a g e %
1088% %
1089% %
1090% %
1091%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1092%
1093% UnregisterMGKImage() removes format registrations made by the
1094% MGK module from the list of supported formats.
1095%
1096% The format of the UnregisterMGKImage method is:
1097%
1098% UnregisterMGKImage(void)
1099%
1100*/
1101ModuleExport void UnregisterMGKImage(void)
1102{
1103 (void) UnregisterMagickInfo("MGK");
1104}
1105
1106/*
1107%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1108% %
1109% %
1110% %
1111% W r i t e M G K I m a g e %
1112% %
1113% %
1114% %
1115%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1116%
1117% WriteMGKImage() writes an image to a file in red, green, and blue
1118% MGK rasterfile format.
1119%
1120% The format of the WriteMGKImage method is:
1121%
1122% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1123%
1124% A description of each parameter follows.
1125%
1126% o image_info: the image info.
1127%
1128% o image: The image.
1129%
1130*/
1131static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1132{
1133 char
1134 buffer[MaxTextExtent];
1135
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1136 MagickBooleanType
1137 status;
1138
1139 MagickOffsetType
1140 scene;
1141
1142 register const PixelPacket
1143 *p;
1144
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1145 register ssize_t
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1146 x;
1147
1148 register unsigned char
1149 *q;
1150
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1151 ssize_t
1152 y;
1153
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1154 unsigned char
1155 *pixels;
1156
1157 /*
1158 Open output image file.
1159 */
1160 assert(image_info != (const ImageInfo *) NULL);
1161 assert(image_info-&gt;signature == MagickSignature);
1162 assert(image != (Image *) NULL);
1163 assert(image-&gt;signature == MagickSignature);
1164 if (image-&gt;debug != MagickFalse)
1165 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1166 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1167 if (status == MagickFalse)
1168 return(status);
1169 scene=0;
1170 do
1171 {
1172 /*
1173 Allocate memory for pixels.
1174 */
1175 if (image-&gt;colorspace != RGBColorspace)
1176 (void) SetImageColorspace(image,RGBColorspace);
1177 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1178 3UL*sizeof(*pixels));
1179 if (pixels == (unsigned char *) NULL)
1180 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1181 /*
1182 Initialize raster file header.
1183 */
1184 (void) WriteBlobString(image,"id=mgk\n");
1185 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1186 image-&gt;columns,image-&gt;rows);
1187 (void) WriteBlobString(image,buffer);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1188 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1189 {
1190 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1191 if (p == (const PixelPacket *) NULL)
1192 break;
1193 q=pixels;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1194 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1195 {
1196 *q++=ScaleQuantumToChar(p-&gt;red);
1197 *q++=ScaleQuantumToChar(p-&gt;green);
1198 *q++=ScaleQuantumToChar(p-&gt;blue);
1199 p++;
1200 }
1201 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1202 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1203 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1204 break;
1205 }
1206 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1207 if (GetNextImageInList(image) == (Image *) NULL)
1208 break;
1209 image=SyncNextImageInList(image);
1210 status=SetImageProgress(image,SaveImagesTag,scene,
1211 GetImageListLength(image));
1212 if (status == MagickFalse)
1213 break;
1214 scene++;
1215 } while (image_info-&gt;adjoin != MagickFalse);
1216 (void) CloseBlob(image);
1217 return(MagickTrue);
1218}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1219</div>
1220
1221<p>To invoke the custom coder from the command line, use these commands:</p>
1222
1223<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>
1224<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>
1225
1226</div>
1227
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1228<h2><a id="filters"></a>Custom Image Filters</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1229<div class="doc-section">
1230
1231<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>
1232
1233<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>
1234
1235<div class="viewport">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1236#include &lt;stdio.h&gt;
1237#include &lt;stdlib.h&gt;
1238#include &lt;string.h&gt;
1239#include &lt;time.h&gt;
1240#include &lt;assert.h&gt;
1241#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1242#include "magick/MagickCore.h"
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1243
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1244/*
1245%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1246% %
1247% %
1248% %
1249% a n a l y z e I m a g e %
1250% %
1251% %
1252% %
1253%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1254%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1255% analyzeImage() computes the brightness and saturation mean, standard
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]1256% deviation, kurtosis and skewness and stores these values as attributes
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1257% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1258%
1259% The format of the analyzeImage method is:
1260%
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1261% size_t analyzeImage(Image *images,const int argc,char **argv,
1262% ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1263%
1264% A description of each parameter follows:
1265%
1266% o image: the address of a structure of type Image.
1267%
1268% o argc: Specifies a pointer to an integer describing the number of
1269% elements in the argument vector.
1270%
1271% o argv: Specifies a pointer to a text array containing the command line
1272% arguments.
1273%
1274% o exception: return any errors or warnings in this structure.
1275%
1276*/
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1277ModuleExport size_t analyzeImage(Image **images,const int argc,const char **argv,
1278 ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1279{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1280 char
1281 text[MaxTextExtent];
1282
1283 double
1284 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1285 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1286 brightness_mean,
1287 brightness_standard_deviation,
1288 brightness_kurtosis,
1289 brightness_skewness,
1290 brightness_sum_x,
1291 brightness_sum_x2,
1292 brightness_sum_x3,
1293 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1294 hue,
1295 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1296 saturation_mean,
1297 saturation_standard_deviation,
1298 saturation_kurtosis,
1299 saturation_skewness,
1300 saturation_sum_x,
1301 saturation_sum_x2,
1302 saturation_sum_x3,
1303 saturation_sum_x4;
1304
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1305 Image
1306 *image;
1307
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1308 assert(images != (Image **) NULL);
1309 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1310 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1311 (void) argc;
1312 (void) argv;
1313 image=(*images);
1314 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1315 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1316 CacheView
1317 *image_view;
1318
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1319 MagickBooleanType
1320 status;
1321
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1322 ssize_t
1323 y;
1324
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1325 brightness_sum_x=0.0;
1326 brightness_sum_x2=0.0;
1327 brightness_sum_x3=0.0;
1328 brightness_sum_x4=0.0;
1329 brightness_mean=0.0;
1330 brightness_standard_deviation=0.0;
1331 brightness_kurtosis=0.0;
1332 brightness_skewness=0.0;
1333 saturation_sum_x=0.0;
1334 saturation_sum_x2=0.0;
1335 saturation_sum_x3=0.0;
1336 saturation_sum_x4=0.0;
1337 saturation_mean=0.0;
1338 saturation_standard_deviation=0.0;
1339 saturation_kurtosis=0.0;
1340 saturation_skewness=0.0;
1341 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1342 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1343 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1344#if defined(MAGICKCORE_OPENMP_SUPPORT)
1345 #pragma omp parallel for schedule(dynamic,4) shared(status)
1346#endif
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1347 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1348 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1349 register const PixelPacket
1350 *p;
1351
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1352 register ssize_t
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1353 x;
1354
1355 if (status == MagickFalse)
1356 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1357 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1358 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1359 {
1360 status=MagickFalse;
1361 continue;
1362 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1363 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1364 {
1365 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1366 brightness*=QuantumRange;
1367 brightness_sum_x+=brightness;
1368 brightness_sum_x2+=brightness*brightness;
1369 brightness_sum_x3+=brightness*brightness*brightness;
1370 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1371 saturation*=QuantumRange;
1372 saturation_sum_x+=saturation;
1373 saturation_sum_x2+=saturation*saturation;
1374 saturation_sum_x3+=saturation*saturation*saturation;
1375 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1376 area++;
1377 p++;
1378 }
1379 }
1380 image_view=DestroyCacheView(image_view);
1381 if (area &lt;= 0.0)
1382 break;
1383 brightness_mean=brightness_sum_x/area;
1384 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1385 (void) SetImageProperty(image,"filter:brightness:mean",text);
1386 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1387 area*brightness_sum_x/area));
1388 (void) FormatMagickString(text,MaxTextExtent,"%g",
1389 brightness_standard_deviation);
1390 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1391 if (brightness_standard_deviation != 0)
1392 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1393 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1394 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1395 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1396 brightness_standard_deviation*brightness_standard_deviation*
1397 brightness_standard_deviation)-3.0;
1398 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1399 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1400 if (brightness_standard_deviation != 0)
1401 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1402 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1403 brightness_mean)/(brightness_standard_deviation*
1404 brightness_standard_deviation*brightness_standard_deviation);
1405 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1406 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1407 saturation_mean=saturation_sum_x/area;
1408 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1409 (void) SetImageProperty(image,"filter:saturation:mean",text);
1410 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1411 area*saturation_sum_x/area));
1412 (void) FormatMagickString(text,MaxTextExtent,"%g",
1413 saturation_standard_deviation);
1414 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1415 if (saturation_standard_deviation != 0)
1416 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1417 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1418 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1419 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1420 saturation_standard_deviation*saturation_standard_deviation*
1421 saturation_standard_deviation)-3.0;
1422 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1423 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1424 if (saturation_standard_deviation != 0)
1425 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1426 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1427 saturation_mean)/(saturation_standard_deviation*
1428 saturation_standard_deviation*saturation_standard_deviation);
1429 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1430 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1431 }
1432 return(MagickImageFilterSignature);
1433}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1434</div>
1435
1436<p>To invoke the custom filter from the command line, use this command:</p>
1437
cristy323f35b2011-03-24 23:05:13 +0000[diff] [blame]1438<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]1439 Format: LOGO (ImageMagick Logo) <br/>
1440 Class: PseudoClass <br/>
1441 Geometry: 640x480 <br/>
1442 ... <br/>
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1443 filter:brightness:kurtosis: 8.17947 <br/>
1444 filter:brightness:mean: 60632.1 <br/>
1445 filter:brightness:skewness: -2.97118 <br/>
1446 filter:brightness:standard-deviation: 13742.1 <br/>
1447 filter:saturation:kurtosis: 4.33554 <br/>
1448 filter:saturation:mean: 5951.55 <br/>
1449 filter:saturation:skewness: 2.42848 <br/>
1450 filter:saturation:standard-deviation: 15575.9</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1451
1452<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>
1453
1454</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1455
1456</div>
1457
1458<div id="linkbar">
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]1459 <span id="linkbar-west">&nbsp;</span>
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cristya8902942010-07-30 00:49:52 +0000[diff] [blame]1462 <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">Studio</a>
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1464 <span id="linkbar-east">&nbsp;</span>
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1466 <div class="footer">
cristy7e41fe82010-12-04 23:12:08 +0000[diff] [blame]1467 <span id="footer-west">&copy; 1999-2011 ImageMagick Studio LLC</span>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1468 <span id="footer-east"> <a href="http://www.imagemagick.org/script/contact.php">Contact the Wizards</a></span>
1469 </div>
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cristya8902942010-07-30 00:49:52 +0000[diff] [blame]1471 <script type="text/javascript">
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