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175
176<div class="main">
177
178
179
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]180<h1>The <em>Magick</em> Behind ImageMagick</h1>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]181<p class="navigation-index">[<a href="#overview">Architecture Overview</a> &bull; <a href="#cache">The Pixel Cache</a> &bull; <a href="#stream">Streaming Pixels</a> &bull; <a href="#properties">Image Properties and Profiles</a> &bull; <a href="#tera-pixel">Large Image Support</a> &bull; <a href="#threads">Threads of Execution</a> &bull; <a href="#distributed">Heterogeneous Distributed Processing</a> &bull; <a href="#coders">Custom Image Coders</a> &bull; <a href="#filters">Custom Image Filters</a>]</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]182
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]183
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]184<div class="doc-section">
185<p>The citizens of Oz were quite content with their benefactor, the all-powerful Wizard. They accepted his wisdom and benevolence without ever questioning the who, why, and where of his power. Like the citizens of Oz, if you feel comfortable that ImageMagick can help you convert, edit, or compose your images without knowing what goes on behind the curtain, feel free to skip this section. However, if you want to know more about the software and algorithms behind ImageMagick, read on. To fully benefit from this discussion, you should be comfortable with image nomenclature and be familiar with computer programming.</p>
186</div>
187
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]188<h2><a id="overview"></a>Architecture Overview</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]189<div class="doc-section">
190
191<p>An image typically consists of a rectangular region of pixels and metadata. To convert, edit, or compose an image in an efficient manner we need convenient access to any pixel anywhere within the region (and sometimes outside the region). And in the case of an image sequence, we need access to any pixel of any region of any image in the sequence. However, there are hundreds of image formats such JPEG, TIFF, PNG, GIF, etc., that makes it difficult to access pixels on demand. Within these formats we find differences in:</p>
192
193<ul>
194 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
195 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
196 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
197 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
198 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
199 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
200</ul>
201
202<p>In addition, some image pixels may require attenuation, some formats permit more than one frame, and some formats contain vector graphics that must first be rasterized (converted from vector to pixels).</p>
203
204<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
205
206<ul>
207 <li>one pixel a time (e.g. pixel at location 10,3)</li>
208 <li>a single scanline (e.g. all pixels from row 4)</li>
209 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
210 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
211 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
212 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
213 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
214 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
215 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
216 <li>a high-dynamic range pixel that can include negative values as well as values that exceed the quantum depth (e.g. -0.00716)</li>
217 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]218 <li>all the pixels in memory to take advantage of speed-ups offered by executing in concert across heterogeneous platforms consisting of CPUs, GPUs, and other processors</li>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]219</ul>
220
221<p>In addition, some images include a clip mask that define which pixels are eligible to be updated. Pixels outside the area defined by the clip mask remain untouched.</p>
222
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]223<p>Given the varied image formats and image processing requirements, we implemented the ImageMagick <a href="#cache">pixel cache</a> to provide convenient sequential or parallel access to any pixel on demand anywhere inside the image region (we call these <a href="#authentic-pixels">authentic pixels</a>) and from any image in a sequence. In addition, the pixel cache permits access to pixels outside the boundaries defined by the image (we call these <a href="#virtual-pixels">virtual pixels</a>).</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]224
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]225<p>In addition to pixels, images have a plethora of <a href="#properties">image properties and profiles</a>. Properties include the well known attributes such as width, height, depth, and colorspace. An image may have optional properties which might include the image author, a comment, a create date, and others. Some images also include profiles for color management, or EXIF, IPTC, 8BIM, or XMP informational profiles. ImageMagick provides command line options and programming methods to get, set, or view image properties or profiles or apply profiles.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]226
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]227<p>ImageMagick consists of more than 400,000 lines of C code and optionally depends on several million lines of code in dependent libraries (e.g. JPEG, PNG, TIFF libraries). Given that, one might expect a huge architecture document. However, a great majority of image processing is simply accessing pixels and its metadata and our simple and elegant implementation makes this easy for the ImageMagick developer. We discuss the implementation of the pixel cache and getting and setting image properties and profiles in the next few sections. Next, we discuss using ImageMagick within a <a href="#threads">thread</a> of execution. In the final sections, we discuss <a href="#coders">image coders</a> to read or write a particular image format followed by a few words on creating a <a href="#filters">filter</a> to access or update pixels based on your custom requirements.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]228
229</div>
230
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]231<h2><a id="cache"></a>The Pixel Cache</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]232<div class="doc-section">
233
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]234<p>The ImageMagick pixel cache is a repository for image pixels with up to 5 channels. The first 4 channels are stored contiguously and an optional second area follows with 1 channel. The channels are at the depth specified when ImageMagick was built. The channel depths are 8 bits-per-pixel component for the Q8 version of ImageMagick, 16 bits-per-pixel component for the Q16 version, and 32 bits-per-pixel component for the Q32 version. By default pixel components are unsigned quantities, however, if you use the <a href="../www/high-dynamic-range.html">high dynamic-range</a> version of ImageMagick, the components are 32-bit floating point. The primary 4 channels can hold any value but typically contain red, green, blue, and alpha intensities or cyan, magenta, yellow, and alpha intensities. The optional fifth channel contains the colormap indexes for colormapped images or the black channel for CMYK images. The pixel cache storage may be heap memory, anonymous memory mapped memory, disk-backed memory mapped, or on disk. The pixel cache is reference-counted. Only the cache properties are copied when the cache is cloned. The cache pixels are subsequently copied only when you signal your intention to update any of the pixels.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]235
236<h3>Create the Pixel Cache</h3>
237<div class="doc-section">
238
239<p>The pixel cache is associated with an image when it is created and it is initialized when you try to get or put pixels. Here are three common methods to associate a pixel cache with an image:</p>
240
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]241<dl>
242<dt>Create an image canvas initialized to the background color:</dt>
243<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]244 image=AllocateImage(image_info);
245 if (SetImageExtent(image,640,480) == MagickFalse)
246 { /* an exception was thrown */ }
247 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
248 SetImageBackgroundColor(image);
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]249</p></dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]250
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]251<dt>Create an image from a JPEG image on disk:</dt>
252<dd><p class="code">
253 (void) strcpy(image_info-&gt;filename,"image.jpg"):
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]254 image=ReadImage(image_info,exception);
255 if (image == (Image *) NULL)
256 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]257</p></dd>
258<dt>Create an image from a memory based image:</dt>
259<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]260 image=BlobToImage(blob_info,blob,extent,exception);
261 if (image == (Image *) NULL)
262 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]263</p></dd>
264</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]265
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]266<p>In our discussion of the pixel cache, we use the <a href="../www/magick-core.html">MagickCore API</a> to illustrate our points, however, the principles are the same for other program interfaces to ImageMagick.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]267
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]268<p>When the pixel cache is initialized, pixels are scaled from whatever bit depth they originated from to that required by the pixel cache. For example, a 1-channel 1-bit monochrome PBM image is scaled to a 4 channel 8-bit RGBA image, if you are using the Q8 version of ImageMagick, and 16-bit RGBA for the Q16 version. You can determine which version you have with the <a href="../www/command-line-options.html#version">&#x2011;version</a> option: </p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]269
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]270<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.7-0 2010-01-01 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]271<p>As you can see, the convenience of the pixel cache sometimes comes with a trade-off in storage (e.g. storing a 1-bit monochrome image as 16-bit RGBA is wasteful) and speed (i.e. storing the entire image in memory is generally slower than accessing one scanline of pixels at a time). In most cases, the benefits of the pixel cache typically outweigh any disadvantages.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]272</div>
273
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]274<h3><a id="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]275<div class="doc-section">
276
277<p>Once the pixel cache is associated with an image, you typically want to get, update, or put pixels into it. We refer to pixels inside the image region as <em>authentic pixels</em> and outside the region as <em>virtual pixels</em>. Use these methods to access the pixels in the cache:</p>
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]278<dl>
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]279 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify or pixels that lie outside the image region (e.g. pixel @ -1,-3)</li>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]280 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
281 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
282 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]283</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]284
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]285<p>Here is a typical <a href="../www/magick-core.html">MagickCore</a> code snippet for manipulating pixels in the pixel cache. In our example, we copy pixels from the input image to the output image and decrease the intensity by 10%:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]286
287<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]288 const PixelPacket
289 *p;
290
291 PixelPacket
292 *q;
293
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]294 ssize_t
295 x,
296 y;
297
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]298 destination=CloneImage(source,source->columns,source->rows,MagickTrue,
299 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]300 if (destination == (Image *) NULL)
301 { /* an exception was thrown */ }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]302 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]303 {
304 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
305 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
306 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
307 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]308 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]309 {
310 q-&gt;red=90*p-&gt;red/100;
311 q-&gt;green=90*p-&gt;green/100;
312 q-&gt;blue=90*p-&gt;blue/100;
313 q-&gt;opacity=90*p-&gt;opacity/100;
314 p++;
315 q++;
316 }
317 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
318 break;
319 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]320 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]321 { /* an exception was thrown */ }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]322</div>
323
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]324<p>When we first create the destination image by cloning the source image, the pixel cache pixels are not copied. They are only copied when you signal your intentions to modify the pixel cache by calling <a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> or <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a>. Use <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> if you want to set new pixel values rather than update existing ones. You could use GetAuthenticPixels() to set pixel values but it is slightly more efficient to use QueueAuthenticPixels() instead. Finally, use <a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]325
326<p>Recall how we mentioned that the indexes of a colormapped image or the black channel of a CMYK image are stored separately. Use <a href="../www/api/cache.html#GetVirtualIndexes">GetVirtualIndexes()</a> (to read the indexes) or <a href="../www/api/cache.html#GetAuthenticIndexes">GetAuthenticIndexes()</a> (to update the indexes) to gain access to this channel. For example, to print the colormap indexes, use:</p>
327
328<pre class="code">
329 const IndexPacket
330 *indexes;
331
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]332 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]333 {
334 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
335 if (p == (const PixelPacket *) NULL)
336 break;
337 indexes=GetVirtualIndexes(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]338 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]339 (void) printf("%d\n",indexes[x];
340 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]341 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]342 /* an exception was thrown */
343</pre>
344
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]345<p>The pixel cache manager decides whether to give you direct or indirect access to the image pixels. In some cases the pixels are staged to an intermediate buffer-- and that is why you must call SyncAuthenticPixels() to ensure this buffer is <em>pushed</em> out to the pixel cache to guarantee the corresponding pixels in the cache are updated. For this reason we recommend that you only read or update a scanline or a few scanlines of pixels at a time. However, you can get any rectangular region of pixels you want. GetAuthenticPixels() requires that the region you request is within the bounds of the image area. For a 640 by 480 image, you can get a scanline of 640 pixels at row 479 but if you ask for a scanline at row 480, an exception is returned (rows are numbered starting at 0). GetVirtualPixels() does not have this constraint. For example,</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]346
347<pre class="code">
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]348 p=GetVirtualPixels(source,-3,-3,source-&gt;columns+3,6,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]349</pre>
350
351<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
352</div>
353
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]354<h3><a id="virtual-pixels"></a>Virtual Pixels</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]355<div class="doc-section">
356
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]357<p>There are a plethora of image processing algorithms that require a neighborhood of pixels about a pixel of interest. The algorithm typically includes a caveat concerning how to handle pixels around the image boundaries, known as edge pixels. With virtual pixels, you do not need to concern yourself about special edge processing other than choosing which virtual pixel method is most appropriate for your algorithm.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]358 <p>Access to the virtual pixels are controlled by the <a href="../www/api/cache.html#SetImageVirtualPixelMethod">SetImageVirtualPixelMethod()</a> method from the MagickCore API or the <a href="../www/command-line-options.html#virtual-pixel">&#x2011;virtual&#x2011;pixel</a> option from the command line. The methods include:</p>
359
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]360<pre class="text" style="font-size: 90%;">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]361 background: the area surrounding the image is the background color
362 black: the area surrounding the image is black
363 checker-tile: alternate squares with image and background color
364 dither: non-random 32x32 dithered pattern
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]365 edge: extend the edge pixel toward infinity (default)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]366 gray: the area surrounding the image is gray
367 horizontal-tile: horizontally tile the image, background color above/below
368 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
369 mirror: mirror tile the image
370 random: choose a random pixel from the image
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]371 tile: tile the image
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]372 transparent: the area surrounding the image is transparent blackness
373 vertical-tile: vertically tile the image, sides are background color
374 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
375 white: the area surrounding the image is white
376</pre>
377
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]378</div>
379
380<h3>Cache Storage and Resource Requirements</h3>
381<div class="doc-section">
382
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]383<p>Recall that this simple and elegant design of the ImageMagick pixel cache comes at a cost in terms of storage and processing speed. The pixel cache storage requirements scales with the area of the image and the bit depth of the pixel components. For example, if we have a 640 by 480 image and we are using the Q16 version of ImageMagick, the pixel cache consumes image <em>width * height * bit-depth / 8 * channels</em> bytes or approximately 2.3 mebibytes (i.e. 640 * 480 * 2 * 4). Not too bad, but what if your image is 25000 by 25000 pixels? The pixel cache requires approximately 4.7 gibibytes of storage. Ouch. ImageMagick accounts for possible huge storage requirements by caching large images to disk rather than memory. Typically the pixel cache is stored in memory using heap memory. If heap memory is exhausted, pixels are stored in in an anonymous map; if the anonymous memory map is exhausted, we create the pixel cache on disk and attempt to memory-map it; and if memory-map memory is exhausted, we simply use standard disk I/O. Disk storage is cheap but it is also very slow, upwards of 1000 times slower than memory. We can get some speed improvements, up to 5 times, if we use memory mapping to the disk-based cache. These decisions about storage are made <em>automagically</em> by the pixel cache manager negotiating with the operating system. However, you can influence how the pixel cache manager allocates the pixel cache with <em>cache resource limits</em>. The limits include:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]384
385<dl class="doc">
386 <dt class="doc">files</dt>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]387 <dd>maximum number of open pixel cache files. When this limit is exceeded, any subsequent pixels cached to disk are closed and reopened on demand. This behavior permits a large number of images to be accessed simultaneously on disk, but without a speed penalty due to repeated open/close calls.</dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]388 <dt class="doc">area</dt>
389 <dd>maximum area in bytes of any one image that can reside in the pixel cache memory. If this limit is exceeded, the image is automagically cached to disk.</dd>
390 <dt class="doc">memory</dt>
391 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
392 <dt class="doc">map</dt>
393 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
394 <dt class="doc">disk</dt>
395 <dd>maximum amount of disk space in bytes permitted for use by the pixel cache. If this limit is exceeded, the pixel cache is not created and a fatal exception is thrown.</dd>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]396 <dt class="doc">thread</dt>
397 <dd>maximum number of threads that are permitted to run in parallel.</dd>
398 <dt class="doc">time</dt>
399 <dd>maximum number of seconds that the process is permitted to execute. When this limit is exceeded, an exception is thrown and processing stops.</dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]400</dl>
401
402<p>To determine the current setting of these limits, use this command:</p>
403
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]404<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span></p><pre class="text">
405File Area Memory Map Disk Thread Time
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]406-------------------------------------------------------------------------------
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]407 768 1.0386GB 3.8692GiB 7.7384GiB unlimited 4 unlimited
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]408</pre>
409
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]410<p>You can set these limits either as a <a href="../www/resources.html#configure">policy</a> (see <a href="../www/source/policy.xml">policy.xml</a>), with an <a href="../www/resources.html#environment">environment variable</a>, with the <a href="../www/command-line-options.html#limit">-limit</a> command line option, or with the <a href="../www/api/resource.html#SetMagickResourceLimit">SetMagickResourceLimit()</a> MagickCore API method. As an example, our online web interface to ImageMagick, <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">ImageMagick Studio</a>, has an area limit of 64 megabytes, a memory limit of 128 mebibytes and a map limit of 256 mebibytes and a disk limit of 1 gigabytes. Since we process multiple simultaneous sessions, we don't want any one session consuming all the available memory. Instead large images are cached to disk. If the image is too large and exceeds the pixel cache disk limit, the program exits. In addition, we place a 60 second time limit to prevent any run-away processing tasks.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]411
412<p>Note, the cache limits are global, meaning if you create several images, the combined resource requirements are compared to the limit to determine the pixel cache storage disposition.</p>
413</div>
414
415<h3>Cache Views</h3>
416<div class="doc-section">
417
418<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() from the MagickCore API can only deal with one pixel cache area per image at a time. Suppose you want to access the first and last scanline from the same image at the same time? The solution is to use a <em>cache view</em>. A cache view permits you to access as many areas simultaneously in the pixel cache as you require. The cache view <a href="../www/api/cache-view.html">methods</a> behave like the previous methods except you must first open a view and close it when you are finished with it. Here is a snippet of MagickCore code that permits us to access two areas of an image simultaneously:</p>
419
420<pre class="code">
421 CacheView
422 *view_1,
423 *view_2;
424
425 view_1=OpenCacheView(source);
426 view_2=OpenCacheView(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]427 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]428 {
429 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]430 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,
431 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]432 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
433 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]434 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]435 {
436 /* do something with u &amp; v here */
437 }
438 }
439 view_1=CloseCacheView(view_1);
440 view_2=CloseCacheView(view_2);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]441 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]442 { /* an exception was thrown */ }
443</pre>
444</div>
445
446<h3>Magick Persistent Cache Format</h3>
447<div class="doc-section">
448
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]449<p>Recall that each image format is decoded by ImageMagick and the pixels are deposited in the pixel cache. If you write an image, the pixels are read from the pixel cache and encoded as required by the format you are writing (e.g. GIF, PNG, etc.). The Magick Persistent Cache (MPC) format is designed to eliminate the overhead of decoding and encoding pixels to and from an image format. MPC writes two files. One, with the extension <kbd>.mpc</kbd>, retains all the properties associated with the image or image sequence (e.g. width, height, colorspace, etc.) and the second, with the extension <kbd>.cache</kbd>, is the pixel cache in the native raw format. When reading an MPC image file, ImageMagick reads the image properties and memory maps the pixel cache on disk eliminating the need for decoding the image pixels. The tradeoff is in disk space. MPC is generally larger in file size than most other image formats.</p>
cristy5063d812010-10-19 16:28:10 +0000[diff] [blame]450<p>The most efficient use of MPC image files is a write-once, read-many-times pattern. For example, your workflow requires extracting random blocks of pixels from the source image. Rather than re-reading and possibly decompressing the source image each time, we use MPC and map the image directly to memory.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]451</div>
452
453<h3>Best Practices</h3>
454<div class="doc-section">
455
456<p>Although you can request any pixel from the pixel cache, any block of pixels, any scanline, multiple scanlines, any row, or multiple rows with the GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels, GetCacheViewVirtualPixels(), GetCacheViewAuthenticPixels(), and QueueCacheViewAuthenticPixels() methods, ImageMagick is optimized to return a few pixels or a few pixels rows at time. There are additional optimizations if you request a single scanline or a few scanlines at a time. These methods also permit random access to the pixel cache, however, ImageMagick is optimized for sequential access.</p>
457
458<p>If you update pixels returned from GetAuthenticPixels() or GetCacheViewAuthenticPixels(), don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to ensure your changes are synchronized with the pixel cache.</p>
459
460<p>Use QueueAuthenticPixels() or QueueCacheViewAuthenticPixels() if you are setting an initial pixel value. The GetAuthenticPixels() or GetCacheViewAuthenticPixels() method reads pixels from the cache and if you are setting an initial pixel value, this read is unnecessary. Don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to push your updates to the pixel cache.</p>
461
462<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() are slightly more efficient than their cache view counter-parts. However, cache views are required if you need access to more than one region of the image simultaneously or if more than one <a href="#threads">thread of execution</a> is accessing the image.</p>
463
464<p>You can request pixels outside the bounds of the image with GetVirtualPixels() or GetCacheViewVirtualPixels(), however, it is more efficient to request pixels within the confines of the image region.</p>
465
466<p>Although you can force the pixel cache to disk using appropriate resource limits, disk access can be upwards of 1000 times slower than memory access. For fast, efficient, access to the pixel cache, try to keep the pixel cache in heap memory or anonymous mapped memory.</p>
467
468<p>The ImageMagick Q16 version of ImageMagick permits you to read and write 16 bit images without scaling but the pixel cache consumes twice as much resources as the Q8 version. If your system has constrained memory or disk resources, consider the Q8 version of ImageMagick. In addition, the Q8 version typically executes faster than the Q16 version.</p>
469
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]470<p>A great majority of image formats and algorithms restrict themselves to a fixed range of pixel values from 0 to some maximum value, for example, the Q16 version of ImageMagick permit intensities from 0 to 65535. High dynamic-range imaging (HDRI), however, permits a far greater dynamic range of exposures (i.e. a large difference between light and dark areas) than standard digital imaging techniques. HDRI accurately represents the wide range of intensity levels found in real scenes ranging from the brightest direct sunlight to the deepest darkest shadows. Enable <a href="../www/high-dynamic-range.html">HDRI</a> at ImageMagick build time to deal with high dynamic-range images, but be mindful that each pixel component is a 32-bit floating point value. In addition, pixel values are not clamped by default so some algorithms may perform differently than the non-HDRI version.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]471
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]472<p>If you are dealing with large images, make sure the pixel cache is written to a disk area with plenty of free space. Under Unix, this is typically <kbd>/tmp</kbd> and for Windows, <kbd>c:/temp</kbd>. You can tell ImageMagick to write the pixel cache to an alternate location with the MAGICK_TEMPORARY_PATH environment variable. For example,</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]473
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]474<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>export MAGICK_TEMPORARY_PATH=/data/magick</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]475
476<p>If you plan on processing the same image many times, consider the MPC format. Reading a MPC image has near-zero overhead because its in the native pixel cache format eliminating the need for decoding the image pixels. Here is an example:</p>
477
478<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.tif image.mpc</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+0+0 +repage 1.png</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+100+0 +repage 2.png</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+200+0 +repage 3.png</span></p>
479<p>MPC is ideal for web sites. It reduces the overhead of reading and writing an image. We use it exclusively at our <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">online image studio</a>.</p>
480</div>
481
482</div>
483
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]484<h2><a id="stream"></a>Streaming Pixels</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]485<div class="doc-section">
486
487<p>ImageMagick provides for streaming pixels as they are read from or written to an image. This has several advantages over the pixel cache. The time and resources consumed by the pixel cache scale with the area of an image, whereas the pixel stream resources scale with the width of an image. The disadvantage is the pixels must be consumed as they are streamed so there is no persistence.</p>
488
489<p>Use <a href="../www/api/stream.html#ReadStream">ReadStream()</a> or <a href="../www/api/stream.html#WriteStream">WriteStream()</a> with an appropriate callback method in your MagickCore program to consume the pixels as they are streaming. Here's an abbreviated example of using ReadStream:</p>
490
491<pre class="code">
492static size_t StreamHandler(const Image *image,const void *pixels,
493 const size_t columns)
494{
495 /* process pixels here */
496 return(columns);
497}
498
499...
500/* invoke the pixel stream here */
501image=ReadStream(image_info,&amp;StreamHandler,exception);
502</pre>
503
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]504<p>We also provide a lightweight tool, <a href="../www/stream.html">stream</a>, to stream one or more pixel components of the image or portion of the image to your choice of storage formats. It writes the pixel components as they are read from the input image a row at a time making <a href="../www/stream.html">stream</a> desirable when working with large images or when you require raw pixel components.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]505
506</div>
507
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]508<h2><a id="properties"></a>Image Properties and Profiles</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]509<div class="doc-section">
510
511<p>Images have metadata associated with them in the form of properties (e.g. width, height, description, etc.) and profiles (e.g. EXIF, IPTC, color management). ImageMagick provides convenient methods to get, set, or update image properties and get, set, update, or apply profiles. Some of the more popular image properties are associated with the Image structure in the MagickCore API. For example:</p>
512
513<pre class="code">
514 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
515</pre>
516
517<p>For a great majority of image properties, such as an image comment or description, we use the <a href="../www/api/property.html#GetImageProperty">GetImageProperty()</a> and <a href="../www/api/property.html#SetImageProperty">SetImageProperty()</a> methods. Here we set a property and fetch it right back:</p>
518
519<pre class="code">
520 const char
521 *comment;
522
523 (void) SetImageProperty(image,"comment","This space for rent");
524 comment=GetImageProperty(image,"comment");
525 if (comment == (const char *) NULL)
526 (void) printf("Image comment: %s\n",comment);
527</pre>
528
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]529<p>ImageMagick supports artifacts with the GetImageArtifact() and SetImageArtifact() methods. Artifacts are stealth properties that are not exported to image formats (e.g. PNG).</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]530
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]531<p>Image profiles are handled with <a href="../www/api/profile.html#GetImageProfile">GetImageProfile()</a>, <a href="../www/api/profile.html#SetImageProfile">SetImageProfile()</a>, and <a href="../www/api/profile.html#ProfileImage">ProfileImage()</a> methods. Here we set a profile and fetch it right back:</p>
532
533<pre class="code">
534 StringInfo
535 *profile;
536
537 profile=AcquireStringInfo(length);
538 SetStringInfoDatum(profile,my_exif_profile);
539 (void) SetImageProfile(image,"EXIF",profile);
540 DestroyStringInfo(profile);
541 profile=GetImageProfile(image,"EXIF");
542 if (profile != (StringInfo *) NULL)
543 (void) PrintStringInfo(stdout,"EXIF",profile);
544</pre>
545
546</div>
547
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]548<h2><a id="tera-pixel"></a>Large Image Support</h2>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]549<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]550<p>ImageMagick can read, process, or write mega-, giga-, or tera-pixel image sizes. An image width or height can range from 1 to 2 giga-pixels on a 32 bit OS and up to 9 exa-pixels on a 64-bit OS. Note, that some image formats have restrictions on image size. For example, Photoshop images are limited to 300,000 pixels for width or height. Here we resize an image to a quarter million pixels square:</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]551
552<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: -resize 250000x250000 logo.miff</span></p>
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]553<p>For large images, ImageMagick will likely create a pixel cache on disk. Make sure you have plenty of temporary disk space. If your default temporary disk partition is too small, tell ImageMagick to use another partition with plenty of free space. For example:</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]554
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]555<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp logo: \ <br/> -resize 250000x250000 logo.miff</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]556<p>To ensure large images do not consume all the memory on your system, force the image pixels to memory-mapped disk with resource limits:</p>
557
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]558<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit memory 16mb \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]559<p>Here we force all image pixels to disk:</p>
560
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]561<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
cristybac7a162010-06-15 19:57:29 +0000[diff] [blame]562<p>Caching pixels to disk is about 1000 times slower than memory. Expect long run times when processing large images on disk with ImageMagick. You can monitor progress with this command:</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]563
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]564<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -monitor -define registry:temporary-path=/data/tmp -limit area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p></div>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]565
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]566<h2><a id="threads"></a>Threads of Execution</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]567<div class="doc-section">
568
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]569<p>Many of ImageMagick's internal algorithms are threaded to take advantage of speed-ups offered by the multicore processor chips. However, you are welcome to use ImageMagick algorithms in your threads of execution with the exception of the MagickCore's GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), or SyncAuthenticPixels() pixel cache methods. These methods are intended for one thread of execution only with the exception of an OpenMP parallel section. To access the pixel cache with more than one thread of execution, use a cache view. We do this for the <a href="../www/api/composite.html#CompositeImage">CompositeImage()</a> method, for example. Suppose we want to composite a single image over a different image in each thread of execution. If we use GetVirtualPixels(), the results are unpredictable because multiple threads would likely be asking for different areas of the pixel cache simultaneously. Instead we use GetCacheViewVirtualPixels() which creates a unique view for each thread of execution ensuring our program behaves properly regardless of how many threads are invoked. The other program interfaces, such as the <a href="../www/magick-wand.html">MagickWand API</a>, are completely thread safe so there are no special precautions for threads of execution.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]570
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]571<p>Here is an example of how ImageMagick can take advantage of threads of execution with the <a href="http://en.wikipedia.org/wiki/OpenMP">OpenMP</a> programming paradigm:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]572
573<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]574{
575 CacheView
576 *image_view;
577
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]578 MagickBooleanType
579 status;
580
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]581 ssize_t
582 y;
583
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]584 status=MagickTrue;
585 image_view=AcquireCacheView(image);
586 #pragma omp parallel for schedule(dynamic,4) shared(status)
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]587 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]588 {
589 register IndexPacket
590 *indexes;
591
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]592 register PixelPacket
593 *q;
594
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]595 register ssize_t
596 x;
597
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]598 if (status == MagickFalse)
599 continue;
600 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
601 if (q == (PixelPacket *) NULL)
602 {
603 status=MagickFalse;
604 continue;
605 }
606 indexes=GetCacheViewAuthenticIndexQueue(image_view);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]607 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]608 {
609 q-&gt;red= ...
610 q-&gt;green= ...
611 q-&gt;blue= ...
612 q-&gt;opacity= ...
613 if (indexes != (IndexPacket *) NULL)
614 indexes[x]= ...
615 q++;
616 }
617 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
618 status=MagickFalse;
619 }
620 image_view=DestroyCacheView(image_view);
621 if (status == MagickFalse)
622 perror("something went wrong");
623}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]624</div>
625
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]626
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]627<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>
628
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]629<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]630
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]631<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]632
633<pre class="text">
634 &lt;policy domain="resource" name="thread" value="2"/>
635</pre>
636
637<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>
638
639<pre class="text">
640 export MAGICK_THREAD_LIMIT=12
641</pre>
642
643<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>
644
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]645</div>
646
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]647<h2><a id="distributed"></a>Heterogeneous Distributed Processing</h2>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]648<div class="doc-section">
649<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>
650
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]651<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]652
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]653<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
654<p>If so, run this command to realize a significant speed-up for image convolution:</p>
655
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]656<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]657<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
658
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]659<p>Here is an example OpenCL kernel that convolves an image:</p>
660
661<div class="viewport">
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]662static inline long ClampToCanvas(const long offset,const ulong range)
663{
664 if (offset &lt; 0L)
665 return(0L);
666 if (offset >= range)
667 return((long) (range-1L));
668 return(offset);
669}
670
671static inline CLQuantum ClampToQuantum(const double value)
672{
673 if (value &lt; 0.0)
674 return((CLQuantum) 0);
675 if (value >= (double) QuantumRange)
676 return((CLQuantum) QuantumRange);
677 return((CLQuantum) (value+0.5));
678}
679
680__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
681 const ulong width,const ulong height,__global CLPixelType *destination)
682{
683 const ulong columns = get_global_size(0);
684 const ulong rows = get_global_size(1);
685
686 const long x = get_global_id(0);
687 const long y = get_global_id(1);
688
689 const double scale = (1.0/QuantumRange);
690 const long mid_width = (width-1)/2;
691 const long mid_height = (height-1)/2;
692 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
693 double gamma = 0.0;
694 register ulong i = 0;
695
696 for (long v=(-mid_height); v &lt;= mid_height; v++)
697 {
698 for (long u=(-mid_width); u &lt;= mid_width; u++)
699 {
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]700 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,
701 columns);
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]702 const double alpha=scale*(QuantumRange-source[index].w);
703 sum.x+=alpha*filter[i]*source[index].x;
704 sum.y+=alpha*filter[i]*source[index].y;
705 sum.z+=alpha*filter[i]*source[index].z;
706 sum.w+=filter[i]*source[index].w;
707 gamma+=alpha*filter[i];
708 i++;
709 }
710 }
711
712 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
713 const ulong index=y*columns+x;
714 destination[index].x=ClampToQuantum(gamma*sum.x);
715 destination[index].y=ClampToQuantum(gamma*sum.y);
716 destination[index].z=ClampToQuantum(gamma*sum.z);
717 destination[index].w=ClampToQuantum(sum.w);
718};
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]719</div>
720
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]721<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]722
723</div>
724
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]725<h2><a id="coders"></a>Custom Image Coders</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]726<div class="doc-section">
727
728<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>
729
730<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>
731
732<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]733/*
734 Include declarations.
735*/
736#include "magick/studio.h"
737#include "magick/blob.h"
738#include "magick/blob-private.h"
739#include "magick/colorspace.h"
740#include "magick/exception.h"
741#include "magick/exception-private.h"
742#include "magick/image.h"
743#include "magick/image-private.h"
744#include "magick/list.h"
745#include "magick/magick.h"
746#include "magick/memory_.h"
747#include "magick/monitor.h"
748#include "magick/monitor-private.h"
749#include "magick/quantum-private.h"
750#include "magick/static.h"
751#include "magick/string_.h"
752#include "magick/module.h"
753
754/*
755 Forward declarations.
756*/
757static MagickBooleanType
758 WriteMGKImage(const ImageInfo *,Image *);
759
760/*
761%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
762% %
763% %
764% %
765% I s M G K %
766% %
767% %
768% %
769%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
770%
771% IsMGK() returns MagickTrue if the image format type, identified by the
772% magick string, is MGK.
773%
774% The format of the IsMGK method is:
775%
776% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
777%
778% A description of each parameter follows:
779%
780% o magick: This string is generally the first few bytes of an image file
781% or blob.
782%
783% o length: Specifies the length of the magick string.
784%
785*/
786static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
787{
788 if (length &lt; 7)
789 return(MagickFalse);
790 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
791 return(MagickTrue);
792 return(MagickFalse);
793}
794
795/*
796%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
797% %
798% %
799% %
800% R e a d M G K I m a g e %
801% %
802% %
803% %
804%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
805%
806% ReadMGKImage() reads a MGK image file and returns it. It allocates
807% the memory necessary for the new Image structure and returns a pointer to
808% the new image.
809%
810% The format of the ReadMGKImage method is:
811%
812% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
813%
814% A description of each parameter follows:
815%
816% o image_info: the image info.
817%
818% o exception: return any errors or warnings in this structure.
819%
820*/
821static Image *ReadMGKImage(const ImageInfo *image_info,
822 ExceptionInfo *exception)
823{
824 char
825 buffer[MaxTextExtent];
826
827 Image
828 *image;
829
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]830 MagickBooleanType
831 status;
832
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]833 register PixelPacket
834 *q;
835
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]836 register size_t
837 x;
838
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]839 register unsigned char
840 *p;
841
842 ssize_t
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]843 count,
844 y;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]845
846 unsigned char
847 *pixels;
848
849 unsigned long
850 columns,
851 rows;
852
853 /*
854 Open image file.
855 */
856 assert(image_info != (const ImageInfo *) NULL);
857 assert(image_info-&gt;signature == MagickSignature);
858 if (image_info-&gt;debug != MagickFalse)
859 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
860 assert(exception != (ExceptionInfo *) NULL);
861 assert(exception-&gt;signature == MagickSignature);
862 image=AcquireImage(image_info);
863 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
864 if (status == MagickFalse)
865 {
866 image=DestroyImageList(image);
867 return((Image *) NULL);
868 }
869 /*
870 Read MGK image.
871 */
872 (void) ReadBlobString(image,buffer); /* read magic number */
873 if (IsMGK(buffer,7) == MagickFalse)
874 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
875 (void) ReadBlobString(image,buffer);
876 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
877 if (count &lt;= 0)
878 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
879 do
880 {
881 /*
882 Initialize image structure.
883 */
884 image-&gt;columns=columns;
885 image-&gt;rows=rows;
886 image-&gt;depth=8;
887 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
888 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
889 break;
890 /*
891 Convert MGK raster image to pixel packets.
892 */
893 if (SetImageExtent(image,0,0) == MagickFalse)
894 {
895 InheritException(exception,&amp;image-&gt;exception);
896 return(DestroyImageList(image));
897 }
898 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
899 if (pixels == (unsigned char *) NULL)
900 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]901 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]902 {
903 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
904 if (count != (ssize_t) (3*image-&gt;columns))
905 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
906 p=pixels;
907 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
908 if (q == (PixelPacket *) NULL)
909 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]910 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]911 {
912 q-&gt;red=ScaleCharToQuantum(*p++);
913 q-&gt;green=ScaleCharToQuantum(*p++);
914 q-&gt;blue=ScaleCharToQuantum(*p++);
915 q++;
916 }
917 if (SyncAuthenticPixels(image,exception) == MagickFalse)
918 break;
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]919 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]920 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
921 break;
922 }
923 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
924 if (EOFBlob(image) != MagickFalse)
925 {
926 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
927 break;
928 }
929 /*
930 Proceed to next image.
931 */
932 if (image_info-&gt;number_scenes != 0)
933 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
934 break;
935 *buffer='\0';
936 (void) ReadBlobString(image,buffer);
937 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
938 if (count != 0)
939 {
940 /*
941 Allocate next image structure.
942 */
943 AcquireNextImage(image_info,image);
944 if (GetNextImageInList(image) == (Image *) NULL)
945 {
946 image=DestroyImageList(image);
947 return((Image *) NULL);
948 }
949 image=SyncNextImageInList(image);
950 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
951 if (status == MagickFalse)
952 break;
953 }
954 } while (count != 0);
955 (void) CloseBlob(image);
956 return(GetFirstImageInList(image));
957}
958
959/*
960%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
961% %
962% %
963% %
964% R e g i s t e r M G K I m a g e %
965% %
966% %
967% %
968%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
969%
970% RegisterMGKImage() adds attributes for the MGK image format to
971% the list of supported formats. The attributes include the image format
972% tag, a method to read and/or write the format, whether the format
973% supports the saving of more than one frame to the same file or blob,
974% whether the format supports native in-memory I/O, and a brief
975% description of the format.
976%
977% The format of the RegisterMGKImage method is:
978%
979% unsigned long RegisterMGKImage(void)
980%
981*/
982ModuleExport unsigned long RegisterMGKImage(void)
983{
984 MagickInfo
985 *entry;
986
987 entry=SetMagickInfo("MGK");
988 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
989 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
990 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
991 entry-&gt;description=ConstantString("MGK");
992 entry-&gt;module=ConstantString("MGK");
993 (void) RegisterMagickInfo(entry);
994 return(MagickImageCoderSignature);
995}
996
997/*
998%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
999% %
1000% %
1001% %
1002% U n r e g i s t e r M G K I m a g e %
1003% %
1004% %
1005% %
1006%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1007%
1008% UnregisterMGKImage() removes format registrations made by the
1009% MGK module from the list of supported formats.
1010%
1011% The format of the UnregisterMGKImage method is:
1012%
1013% UnregisterMGKImage(void)
1014%
1015*/
1016ModuleExport void UnregisterMGKImage(void)
1017{
1018 (void) UnregisterMagickInfo("MGK");
1019}
1020
1021/*
1022%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1023% %
1024% %
1025% %
1026% W r i t e M G K I m a g e %
1027% %
1028% %
1029% %
1030%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1031%
1032% WriteMGKImage() writes an image to a file in red, green, and blue
1033% MGK rasterfile format.
1034%
1035% The format of the WriteMGKImage method is:
1036%
1037% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1038%
1039% A description of each parameter follows.
1040%
1041% o image_info: the image info.
1042%
1043% o image: The image.
1044%
1045*/
1046static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1047{
1048 char
1049 buffer[MaxTextExtent];
1050
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1051 MagickBooleanType
1052 status;
1053
1054 MagickOffsetType
1055 scene;
1056
1057 register const PixelPacket
1058 *p;
1059
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1060 register ssize_t
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1061 x;
1062
1063 register unsigned char
1064 *q;
1065
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1066 ssize_t
1067 y;
1068
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1069 unsigned char
1070 *pixels;
1071
1072 /*
1073 Open output image file.
1074 */
1075 assert(image_info != (const ImageInfo *) NULL);
1076 assert(image_info-&gt;signature == MagickSignature);
1077 assert(image != (Image *) NULL);
1078 assert(image-&gt;signature == MagickSignature);
1079 if (image-&gt;debug != MagickFalse)
1080 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1081 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1082 if (status == MagickFalse)
1083 return(status);
1084 scene=0;
1085 do
1086 {
1087 /*
1088 Allocate memory for pixels.
1089 */
1090 if (image-&gt;colorspace != RGBColorspace)
1091 (void) SetImageColorspace(image,RGBColorspace);
1092 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1093 3UL*sizeof(*pixels));
1094 if (pixels == (unsigned char *) NULL)
1095 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1096 /*
1097 Initialize raster file header.
1098 */
1099 (void) WriteBlobString(image,"id=mgk\n");
1100 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1101 image-&gt;columns,image-&gt;rows);
1102 (void) WriteBlobString(image,buffer);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1103 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1104 {
1105 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1106 if (p == (const PixelPacket *) NULL)
1107 break;
1108 q=pixels;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1109 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1110 {
1111 *q++=ScaleQuantumToChar(p-&gt;red);
1112 *q++=ScaleQuantumToChar(p-&gt;green);
1113 *q++=ScaleQuantumToChar(p-&gt;blue);
1114 p++;
1115 }
1116 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1117 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1118 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1119 break;
1120 }
1121 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1122 if (GetNextImageInList(image) == (Image *) NULL)
1123 break;
1124 image=SyncNextImageInList(image);
1125 status=SetImageProgress(image,SaveImagesTag,scene,
1126 GetImageListLength(image));
1127 if (status == MagickFalse)
1128 break;
1129 scene++;
1130 } while (image_info-&gt;adjoin != MagickFalse);
1131 (void) CloseBlob(image);
1132 return(MagickTrue);
1133}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1134</div>
1135
1136<p>To invoke the custom coder from the command line, use these commands:</p>
1137
1138<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>
1139<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>
1140
1141</div>
1142
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1143<h2><a id="filters"></a>Custom Image Filters</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1144<div class="doc-section">
1145
1146<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>
1147
1148<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>
1149
1150<div class="viewport">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1151#include &lt;stdio.h&gt;
1152#include &lt;stdlib.h&gt;
1153#include &lt;string.h&gt;
1154#include &lt;time.h&gt;
1155#include &lt;assert.h&gt;
1156#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1157#include "magick/MagickCore.h"
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1158
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1159/*
1160%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1161% %
1162% %
1163% %
1164% a n a l y z e I m a g e %
1165% %
1166% %
1167% %
1168%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1169%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1170% analyzeImage() computes the brightness and saturation mean, standard
1171% deviation, kurtosis and skewness and stores these values as attributes
1172% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1173%
1174% The format of the analyzeImage method is:
1175%
1176% unsigned long analyzeImage(Image *images,const int argc,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1177% char **argv,ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1178%
1179% A description of each parameter follows:
1180%
1181% o image: the address of a structure of type Image.
1182%
1183% o argc: Specifies a pointer to an integer describing the number of
1184% elements in the argument vector.
1185%
1186% o argv: Specifies a pointer to a text array containing the command line
1187% arguments.
1188%
1189% o exception: return any errors or warnings in this structure.
1190%
1191*/
1192ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1193 const char **argv,ExceptionInfo *exception)
1194{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1195 char
1196 text[MaxTextExtent];
1197
1198 double
1199 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1200 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1201 brightness_mean,
1202 brightness_standard_deviation,
1203 brightness_kurtosis,
1204 brightness_skewness,
1205 brightness_sum_x,
1206 brightness_sum_x2,
1207 brightness_sum_x3,
1208 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1209 hue,
1210 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1211 saturation_mean,
1212 saturation_standard_deviation,
1213 saturation_kurtosis,
1214 saturation_skewness,
1215 saturation_sum_x,
1216 saturation_sum_x2,
1217 saturation_sum_x3,
1218 saturation_sum_x4;
1219
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1220 Image
1221 *image;
1222
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1223 assert(images != (Image **) NULL);
1224 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1225 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1226 (void) argc;
1227 (void) argv;
1228 image=(*images);
1229 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1230 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1231 CacheView
1232 *image_view;
1233
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1234 MagickBooleanType
1235 status;
1236
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1237 ssize_t
1238 y;
1239
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1240 brightness_sum_x=0.0;
1241 brightness_sum_x2=0.0;
1242 brightness_sum_x3=0.0;
1243 brightness_sum_x4=0.0;
1244 brightness_mean=0.0;
1245 brightness_standard_deviation=0.0;
1246 brightness_kurtosis=0.0;
1247 brightness_skewness=0.0;
1248 saturation_sum_x=0.0;
1249 saturation_sum_x2=0.0;
1250 saturation_sum_x3=0.0;
1251 saturation_sum_x4=0.0;
1252 saturation_mean=0.0;
1253 saturation_standard_deviation=0.0;
1254 saturation_kurtosis=0.0;
1255 saturation_skewness=0.0;
1256 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1257 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1258 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1259#if defined(MAGICKCORE_OPENMP_SUPPORT)
1260 #pragma omp parallel for schedule(dynamic,4) shared(status)
1261#endif
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1262 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1263 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1264 register const PixelPacket
1265 *p;
1266
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1267 register ssize_t
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1268 x;
1269
1270 if (status == MagickFalse)
1271 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1272 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1273 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1274 {
1275 status=MagickFalse;
1276 continue;
1277 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1278 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1279 {
1280 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1281 brightness*=QuantumRange;
1282 brightness_sum_x+=brightness;
1283 brightness_sum_x2+=brightness*brightness;
1284 brightness_sum_x3+=brightness*brightness*brightness;
1285 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1286 saturation*=QuantumRange;
1287 saturation_sum_x+=saturation;
1288 saturation_sum_x2+=saturation*saturation;
1289 saturation_sum_x3+=saturation*saturation*saturation;
1290 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1291 area++;
1292 p++;
1293 }
1294 }
1295 image_view=DestroyCacheView(image_view);
1296 if (area &lt;= 0.0)
1297 break;
1298 brightness_mean=brightness_sum_x/area;
1299 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1300 (void) SetImageProperty(image,"filter:brightness:mean",text);
1301 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1302 area*brightness_sum_x/area));
1303 (void) FormatMagickString(text,MaxTextExtent,"%g",
1304 brightness_standard_deviation);
1305 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1306 if (brightness_standard_deviation != 0)
1307 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1308 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1309 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1310 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1311 brightness_standard_deviation*brightness_standard_deviation*
1312 brightness_standard_deviation)-3.0;
1313 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1314 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1315 if (brightness_standard_deviation != 0)
1316 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1317 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1318 brightness_mean)/(brightness_standard_deviation*
1319 brightness_standard_deviation*brightness_standard_deviation);
1320 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1321 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1322 saturation_mean=saturation_sum_x/area;
1323 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1324 (void) SetImageProperty(image,"filter:saturation:mean",text);
1325 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1326 area*saturation_sum_x/area));
1327 (void) FormatMagickString(text,MaxTextExtent,"%g",
1328 saturation_standard_deviation);
1329 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1330 if (saturation_standard_deviation != 0)
1331 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1332 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1333 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1334 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1335 saturation_standard_deviation*saturation_standard_deviation*
1336 saturation_standard_deviation)-3.0;
1337 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1338 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1339 if (saturation_standard_deviation != 0)
1340 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1341 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1342 saturation_mean)/(saturation_standard_deviation*
1343 saturation_standard_deviation*saturation_standard_deviation);
1344 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1345 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1346 }
1347 return(MagickImageFilterSignature);
1348}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1349</div>
1350
1351<p>To invoke the custom filter from the command line, use this command:</p>
1352
1353<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/>
1354 Format: LOGO (ImageMagick Logo) <br/>
1355 Class: PseudoClass <br/>
1356 Geometry: 640x480 <br/>
1357 ... <br/>
1358 filter:brightness:kurtosis: 8.98864 <br/>
1359 filter:brightness:mean: 238.096 <br/>
1360 filter:brightness:skewness: -3.04519 <br/>
1361 filter:brightness:standard-deviation: 46.3286 <br/>
1362 filter:saturation:kurtosis: 5.9137 <br/>
1363 filter:saturation:mean: 23.4635 <br/>
1364 filter:saturation:skewness: 2.71874 <br/>
1365 filter:saturation:standard-deviation: 64.7734</span></p>
1366
1367<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>
1368
1369</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1370
1371</div>
1372
1373<div id="linkbar">
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]1374 <span id="linkbar-west">&nbsp;</span>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1375 <span id="linkbar-center">
1376 <a href="http://www.imagemagick.org/discourse-server/">Discourse Server</a> &bull;
cristya8902942010-07-30 00:49:52 +0000[diff] [blame]1377 <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">Studio</a>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1378 </span>
1379 <span id="linkbar-east">&nbsp;</span>
1380 </div>
1381 <div class="footer">
cristy7e41fe82010-12-04 23:12:08 +0000[diff] [blame]1382 <span id="footer-west">&copy; 1999-2011 ImageMagick Studio LLC</span>
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