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172
173
174
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]175<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]176
177<div class="doc-section">
178<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>
179</div>
180
181<h2><a name="overview"></a>Architecture Overview</h2>
182<div class="doc-section">
183
184<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>
185
186<ul>
187 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
188 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
189 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
190 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
191 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
192 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
193</ul>
194
195<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>
196
197<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
198
199<ul>
200 <li>one pixel a time (e.g. pixel at location 10,3)</li>
201 <li>a single scanline (e.g. all pixels from row 4)</li>
202 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
203 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
204 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
205 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
206 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
207 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
208 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
209 <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>
210 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]211 <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]212</ul>
213
214<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>
215
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]216<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]217
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]218<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]219
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]220<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]221
222</div>
223
224<h2><a name="cache"></a>The Pixel Cache</h2>
225<div class="doc-section">
226
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]227<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]228
229<h3>Create the Pixel Cache</h3>
230<div class="doc-section">
231
232<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>
233
234<h4>Create an image canvas initialized to the background color:</h4>
235<p class="code">
236 image=AllocateImage(image_info);
237 if (SetImageExtent(image,640,480) == MagickFalse)
238 { /* an exception was thrown */ }
239 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
240 SetImageBackgroundColor(image);
241</p>
242
243<h4>Create an image from a JPEG image on disk:</h4>
244<p class="code"> (void) strcpy(image_info-&gt;filename,"image.jpg"):
245 image=ReadImage(image_info,exception);
246 if (image == (Image *) NULL)
247 { /* an exception was thrown */ }
248</p>
249<h4>Create an image from a memory based image:</h4>
250<p class="code">
251 image=BlobToImage(blob_info,blob,extent,exception);
252 if (image == (Image *) NULL)
253 { /* an exception was thrown */ }
254</p>
255
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]256<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]257
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]258<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]259
cristy9cb69bc2010-10-14 00:45:05 +0000[diff] [blame]260<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.5-0 2010-09-21 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]261<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]262</div>
263
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]264<h3><a name="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]265<div class="doc-section">
266
267<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>
268<ul>
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]269 <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]270 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
271 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
272 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
273</ul>
274
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]275<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]276
277<div class="viewport">
278<pre class="code">
279 long
280 x,
281 y;
282
283 const PixelPacket
284 *p;
285
286 PixelPacket
287 *q;
288
289 destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
290 if (destination == (Image *) NULL)
291 { /* an exception was thrown */ }
292 for (y=0; y &lt; (long) source-&gt;rows; y++)
293 {
294 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
295 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
296 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
297 break;
298 for (x=0; x &lt; (long) source-&gt;columns; x++)
299 {
300 q-&gt;red=90*p-&gt;red/100;
301 q-&gt;green=90*p-&gt;green/100;
302 q-&gt;blue=90*p-&gt;blue/100;
303 q-&gt;opacity=90*p-&gt;opacity/100;
304 p++;
305 q++;
306 }
307 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
308 break;
309 }
310 if (y &lt; (long) source-&gt;rows)
311 { /* an exception was thrown */ }
312</pre>
313</div>
314
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]315<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]316
317<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>
318
319<pre class="code">
320 const IndexPacket
321 *indexes;
322
323 for (y=0; y &lt; (long) source-&gt;rows; y++)
324 {
325 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
326 if (p == (const PixelPacket *) NULL)
327 break;
328 indexes=GetVirtualIndexes(source);
329 for (x=0; x &lt; (long) source-&gt;columns; x++)
330 (void) printf("%d\n",indexes[x];
331 }
332 if (y &lt; (long) source-&gt;rows)
333 /* an exception was thrown */
334</pre>
335
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]336<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]337
338<pre class="code">
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]339 p=GetVirtualPixels(source,-3,-3,source-&gt;columns+3,6,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]340</pre>
341
342<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
343</div>
344
345<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
346<div class="doc-section">
347
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]348<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]349 <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>
350
351<pre class="text">
352 background: the area surrounding the image is the background color
353 black: the area surrounding the image is black
354 checker-tile: alternate squares with image and background color
355 dither: non-random 32x32 dithered pattern
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]356 edge: extend the edge pixel toward infinity (default)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]357 gray: the area surrounding the image is gray
358 horizontal-tile: horizontally tile the image, background color above/below
359 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
360 mirror: mirror tile the image
361 random: choose a random pixel from the image
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]362 tile: tile the image
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]363 transparent: the area surrounding the image is transparent blackness
364 vertical-tile: vertically tile the image, sides are background color
365 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
366 white: the area surrounding the image is white
367</pre>
368
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]369</div>
370
371<h3>Cache Storage and Resource Requirements</h3>
372<div class="doc-section">
373
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]374<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]375
376<dl class="doc">
377 <dt class="doc">files</dt>
378 <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 with a speed penalty due to repeated open/close calls.</dd>
379 <dt class="doc">area</dt>
380 <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>
381 <dt class="doc">memory</dt>
382 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
383 <dt class="doc">map</dt>
384 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
385 <dt class="doc">disk</dt>
386 <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>
387</dl>
388
389<p>To determine the current setting of these limits, use this command:</p>
390
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]391<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span><span class='crtout'><pre>File Area Memory Map Disk Thread Time
392-------------------------------------------------------------------------------
393 768 12.443GB 8.6917GiB 23.178GiB 18.446744EB 8 unlimited</pre></span></p>
cristyb15553d2010-07-03 22:53:14 +0000[diff] [blame]394<p>You can set these limits either as a <a href="../www/resources.html#configure">policy</a> (see <kbd>policy.xml</kbd>), 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]395
396<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>
397</div>
398
399<h3>Cache Views</h3>
400<div class="doc-section">
401
402<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>
403
404<pre class="code">
405 CacheView
406 *view_1,
407 *view_2;
408
409 view_1=OpenCacheView(source);
410 view_2=OpenCacheView(source);
411 for (y=0; y &lt; (long) source-&gt;rows; y++)
412 {
413 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
414 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,exception);
415 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
416 break;
417 for (x=0; x &lt; (long) source-&gt;columns; x++)
418 {
419 /* do something with u &amp; v here */
420 }
421 }
422 view_1=CloseCacheView(view_1);
423 view_2=CloseCacheView(view_2);
424 if (y &lt; (long) source-&gt;rows)
425 { /* an exception was thrown */ }
426</pre>
427</div>
428
429<h3>Magick Persistent Cache Format</h3>
430<div class="doc-section">
431
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]432<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^]433<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]434</div>
435
436<h3>Best Practices</h3>
437<div class="doc-section">
438
439<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>
440
441<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>
442
443<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>
444
445<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>
446
447<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>
448
449<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>
450
451<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>
452
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]453<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]454
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]455<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]456
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]457<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]458
459<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>
460
461<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>
462<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>
463</div>
464
465</div>
466
467<h2><a name="stream"></a>Streaming Pixels</h2>
468<div class="doc-section">
469
470<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>
471
472<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>
473
474<pre class="code">
475static size_t StreamHandler(const Image *image,const void *pixels,
476 const size_t columns)
477{
478 /* process pixels here */
479 return(columns);
480}
481
482...
483/* invoke the pixel stream here */
484image=ReadStream(image_info,&amp;StreamHandler,exception);
485</pre>
486
487<p>We also provide a lightweight tool, <a name="stream"></a><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 name="stream"></a><a href="../www/stream.html">stream</a> desirable when working with large images or when you require raw pixel components.</p>
488
489</div>
490
491<h2><a name="properties"></a>Image Properties and Profiles</h2>
492<div class="doc-section">
493
494<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>
495
496<pre class="code">
497 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
498</pre>
499
500<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>
501
502<pre class="code">
503 const char
504 *comment;
505
506 (void) SetImageProperty(image,"comment","This space for rent");
507 comment=GetImageProperty(image,"comment");
508 if (comment == (const char *) NULL)
509 (void) printf("Image comment: %s\n",comment);
510</pre>
511
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]512<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]513
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]514<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>
515
516<pre class="code">
517 StringInfo
518 *profile;
519
520 profile=AcquireStringInfo(length);
521 SetStringInfoDatum(profile,my_exif_profile);
522 (void) SetImageProfile(image,"EXIF",profile);
523 DestroyStringInfo(profile);
524 profile=GetImageProfile(image,"EXIF");
525 if (profile != (StringInfo *) NULL)
526 (void) PrintStringInfo(stdout,"EXIF",profile);
527</pre>
528
529</div>
530
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]531<h2><a name="tera-pixel"></a>Large Image Support</h2>
532<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]533<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]534
535<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]536<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]537
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]538<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]539<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>
540
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]541<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]542<p>Here we force all image pixels to disk:</p>
543
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]544<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]545<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]546
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]547<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]548
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]549<h2><a name="threads"></a>Threads of Execution</h2>
550<div class="doc-section">
551
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]552<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. 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]553
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]554<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]555
556<div class="viewport">
557<pre class="code">
558{
559 CacheView
560 *image_view;
561
562 long
563 y;
564
565 MagickBooleanType
566 status;
567
568 status=MagickTrue;
569 image_view=AcquireCacheView(image);
570 #pragma omp parallel for schedule(dynamic,4) shared(status)
571 for (y=0; y &lt; (long) image-&gt;rows; y++)
572 {
573 register IndexPacket
574 *indexes;
575
576 register long
577 x;
578
579 register PixelPacket
580 *q;
581
582 if (status == MagickFalse)
583 continue;
584 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
585 if (q == (PixelPacket *) NULL)
586 {
587 status=MagickFalse;
588 continue;
589 }
590 indexes=GetCacheViewAuthenticIndexQueue(image_view);
591 for (x=0; x &lt; (long) image-&gt;columns; x++)
592 {
593 q-&gt;red= ...
594 q-&gt;green= ...
595 q-&gt;blue= ...
596 q-&gt;opacity= ...
597 if (indexes != (IndexPacket *) NULL)
598 indexes[x]= ...
599 q++;
600 }
601 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
602 status=MagickFalse;
603 }
604 image_view=DestroyCacheView(image_view);
605 if (status == MagickFalse)
606 perror("something went wrong");
607}
608</pre>
609</div>
610
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]611
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]612<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>
613
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]614<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]615
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]616<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 thread 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]617</div>
618
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]619<h2><a name="distributed"></a>Heterogeneous Distributed Processing</h2>
620<div class="doc-section">
621<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>
622
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]623<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]624
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]625<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
626<p>If so, run this command to realize a significant speed-up for image convolution:</p>
627
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]628<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]629<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
630
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]631<p>Here is an example OpenCL kernel that convolves an image:</p>
632
633<div class="viewport">
634<pre class="code">
635static inline long ClampToCanvas(const long offset,const ulong range)
636{
637 if (offset &lt; 0L)
638 return(0L);
639 if (offset >= range)
640 return((long) (range-1L));
641 return(offset);
642}
643
644static inline CLQuantum ClampToQuantum(const double value)
645{
646 if (value &lt; 0.0)
647 return((CLQuantum) 0);
648 if (value >= (double) QuantumRange)
649 return((CLQuantum) QuantumRange);
650 return((CLQuantum) (value+0.5));
651}
652
653__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
654 const ulong width,const ulong height,__global CLPixelType *destination)
655{
656 const ulong columns = get_global_size(0);
657 const ulong rows = get_global_size(1);
658
659 const long x = get_global_id(0);
660 const long y = get_global_id(1);
661
662 const double scale = (1.0/QuantumRange);
663 const long mid_width = (width-1)/2;
664 const long mid_height = (height-1)/2;
665 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
666 double gamma = 0.0;
667 register ulong i = 0;
668
669 for (long v=(-mid_height); v &lt;= mid_height; v++)
670 {
671 for (long u=(-mid_width); u &lt;= mid_width; u++)
672 {
673 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,columns);
674 const double alpha=scale*(QuantumRange-source[index].w);
675 sum.x+=alpha*filter[i]*source[index].x;
676 sum.y+=alpha*filter[i]*source[index].y;
677 sum.z+=alpha*filter[i]*source[index].z;
678 sum.w+=filter[i]*source[index].w;
679 gamma+=alpha*filter[i];
680 i++;
681 }
682 }
683
684 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
685 const ulong index=y*columns+x;
686 destination[index].x=ClampToQuantum(gamma*sum.x);
687 destination[index].y=ClampToQuantum(gamma*sum.y);
688 destination[index].z=ClampToQuantum(gamma*sum.z);
689 destination[index].w=ClampToQuantum(sum.w);
690};
691</pre>
692</div>
693
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]694<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]695
696</div>
697
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]698<h2><a name="coders"></a>Custom Image Coders</h2>
699<div class="doc-section">
700
701<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>
702
703<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>
704
705<div class="viewport">
706<pre class="code">
707/*
708 Include declarations.
709*/
710#include "magick/studio.h"
711#include "magick/blob.h"
712#include "magick/blob-private.h"
713#include "magick/colorspace.h"
714#include "magick/exception.h"
715#include "magick/exception-private.h"
716#include "magick/image.h"
717#include "magick/image-private.h"
718#include "magick/list.h"
719#include "magick/magick.h"
720#include "magick/memory_.h"
721#include "magick/monitor.h"
722#include "magick/monitor-private.h"
723#include "magick/quantum-private.h"
724#include "magick/static.h"
725#include "magick/string_.h"
726#include "magick/module.h"
727
728/*
729 Forward declarations.
730*/
731static MagickBooleanType
732 WriteMGKImage(const ImageInfo *,Image *);
733
734/*
735%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
736% %
737% %
738% %
739% I s M G K %
740% %
741% %
742% %
743%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
744%
745% IsMGK() returns MagickTrue if the image format type, identified by the
746% magick string, is MGK.
747%
748% The format of the IsMGK method is:
749%
750% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
751%
752% A description of each parameter follows:
753%
754% o magick: This string is generally the first few bytes of an image file
755% or blob.
756%
757% o length: Specifies the length of the magick string.
758%
759*/
760static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
761{
762 if (length &lt; 7)
763 return(MagickFalse);
764 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
765 return(MagickTrue);
766 return(MagickFalse);
767}
768
769/*
770%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
771% %
772% %
773% %
774% R e a d M G K I m a g e %
775% %
776% %
777% %
778%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
779%
780% ReadMGKImage() reads a MGK image file and returns it. It allocates
781% the memory necessary for the new Image structure and returns a pointer to
782% the new image.
783%
784% The format of the ReadMGKImage method is:
785%
786% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
787%
788% A description of each parameter follows:
789%
790% o image_info: the image info.
791%
792% o exception: return any errors or warnings in this structure.
793%
794*/
795static Image *ReadMGKImage(const ImageInfo *image_info,
796 ExceptionInfo *exception)
797{
798 char
799 buffer[MaxTextExtent];
800
801 Image
802 *image;
803
804 long
805 y;
806
807 MagickBooleanType
808 status;
809
810 register long
811 x;
812
813 register PixelPacket
814 *q;
815
816 register unsigned char
817 *p;
818
819 ssize_t
820 count;
821
822 unsigned char
823 *pixels;
824
825 unsigned long
826 columns,
827 rows;
828
829 /*
830 Open image file.
831 */
832 assert(image_info != (const ImageInfo *) NULL);
833 assert(image_info-&gt;signature == MagickSignature);
834 if (image_info-&gt;debug != MagickFalse)
835 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
836 assert(exception != (ExceptionInfo *) NULL);
837 assert(exception-&gt;signature == MagickSignature);
838 image=AcquireImage(image_info);
839 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
840 if (status == MagickFalse)
841 {
842 image=DestroyImageList(image);
843 return((Image *) NULL);
844 }
845 /*
846 Read MGK image.
847 */
848 (void) ReadBlobString(image,buffer); /* read magic number */
849 if (IsMGK(buffer,7) == MagickFalse)
850 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
851 (void) ReadBlobString(image,buffer);
852 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
853 if (count &lt;= 0)
854 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
855 do
856 {
857 /*
858 Initialize image structure.
859 */
860 image-&gt;columns=columns;
861 image-&gt;rows=rows;
862 image-&gt;depth=8;
863 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
864 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
865 break;
866 /*
867 Convert MGK raster image to pixel packets.
868 */
869 if (SetImageExtent(image,0,0) == MagickFalse)
870 {
871 InheritException(exception,&amp;image-&gt;exception);
872 return(DestroyImageList(image));
873 }
874 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
875 if (pixels == (unsigned char *) NULL)
876 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
877 for (y=0; y &lt; (long) image-&gt;rows; y++)
878 {
879 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
880 if (count != (ssize_t) (3*image-&gt;columns))
881 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
882 p=pixels;
883 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
884 if (q == (PixelPacket *) NULL)
885 break;
886 for (x=0; x &lt; (long) image-&gt;columns; x++)
887 {
888 q-&gt;red=ScaleCharToQuantum(*p++);
889 q-&gt;green=ScaleCharToQuantum(*p++);
890 q-&gt;blue=ScaleCharToQuantum(*p++);
891 q++;
892 }
893 if (SyncAuthenticPixels(image,exception) == MagickFalse)
894 break;
895 if ((image-&gt;previous == (Image *) NULL) &&
896 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
897 break;
898 }
899 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
900 if (EOFBlob(image) != MagickFalse)
901 {
902 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
903 break;
904 }
905 /*
906 Proceed to next image.
907 */
908 if (image_info-&gt;number_scenes != 0)
909 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
910 break;
911 *buffer='\0';
912 (void) ReadBlobString(image,buffer);
913 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
914 if (count != 0)
915 {
916 /*
917 Allocate next image structure.
918 */
919 AcquireNextImage(image_info,image);
920 if (GetNextImageInList(image) == (Image *) NULL)
921 {
922 image=DestroyImageList(image);
923 return((Image *) NULL);
924 }
925 image=SyncNextImageInList(image);
926 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
927 if (status == MagickFalse)
928 break;
929 }
930 } while (count != 0);
931 (void) CloseBlob(image);
932 return(GetFirstImageInList(image));
933}
934
935/*
936%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
937% %
938% %
939% %
940% R e g i s t e r M G K I m a g e %
941% %
942% %
943% %
944%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
945%
946% RegisterMGKImage() adds attributes for the MGK image format to
947% the list of supported formats. The attributes include the image format
948% tag, a method to read and/or write the format, whether the format
949% supports the saving of more than one frame to the same file or blob,
950% whether the format supports native in-memory I/O, and a brief
951% description of the format.
952%
953% The format of the RegisterMGKImage method is:
954%
955% unsigned long RegisterMGKImage(void)
956%
957*/
958ModuleExport unsigned long RegisterMGKImage(void)
959{
960 MagickInfo
961 *entry;
962
963 entry=SetMagickInfo("MGK");
964 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
965 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
966 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
967 entry-&gt;description=ConstantString("MGK");
968 entry-&gt;module=ConstantString("MGK");
969 (void) RegisterMagickInfo(entry);
970 return(MagickImageCoderSignature);
971}
972
973/*
974%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
975% %
976% %
977% %
978% U n r e g i s t e r M G K I m a g e %
979% %
980% %
981% %
982%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
983%
984% UnregisterMGKImage() removes format registrations made by the
985% MGK module from the list of supported formats.
986%
987% The format of the UnregisterMGKImage method is:
988%
989% UnregisterMGKImage(void)
990%
991*/
992ModuleExport void UnregisterMGKImage(void)
993{
994 (void) UnregisterMagickInfo("MGK");
995}
996
997/*
998%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
999% %
1000% %
1001% %
1002% W r i t e M G K I m a g e %
1003% %
1004% %
1005% %
1006%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1007%
1008% WriteMGKImage() writes an image to a file in red, green, and blue
1009% MGK rasterfile format.
1010%
1011% The format of the WriteMGKImage method is:
1012%
1013% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1014%
1015% A description of each parameter follows.
1016%
1017% o image_info: the image info.
1018%
1019% o image: The image.
1020%
1021*/
1022static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1023{
1024 char
1025 buffer[MaxTextExtent];
1026
1027 long
1028 y;
1029
1030 MagickBooleanType
1031 status;
1032
1033 MagickOffsetType
1034 scene;
1035
1036 register const PixelPacket
1037 *p;
1038
1039 register long
1040 x;
1041
1042 register unsigned char
1043 *q;
1044
1045 unsigned char
1046 *pixels;
1047
1048 /*
1049 Open output image file.
1050 */
1051 assert(image_info != (const ImageInfo *) NULL);
1052 assert(image_info-&gt;signature == MagickSignature);
1053 assert(image != (Image *) NULL);
1054 assert(image-&gt;signature == MagickSignature);
1055 if (image-&gt;debug != MagickFalse)
1056 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1057 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1058 if (status == MagickFalse)
1059 return(status);
1060 scene=0;
1061 do
1062 {
1063 /*
1064 Allocate memory for pixels.
1065 */
1066 if (image-&gt;colorspace != RGBColorspace)
1067 (void) SetImageColorspace(image,RGBColorspace);
1068 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1069 3UL*sizeof(*pixels));
1070 if (pixels == (unsigned char *) NULL)
1071 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1072 /*
1073 Initialize raster file header.
1074 */
1075 (void) WriteBlobString(image,"id=mgk\n");
1076 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1077 image-&gt;columns,image-&gt;rows);
1078 (void) WriteBlobString(image,buffer);
1079 for (y=0; y &lt; (long) image-&gt;rows; y++)
1080 {
1081 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1082 if (p == (const PixelPacket *) NULL)
1083 break;
1084 q=pixels;
1085 for (x=0; x &lt; (long) image-&gt;columns; x++)
1086 {
1087 *q++=ScaleQuantumToChar(p-&gt;red);
1088 *q++=ScaleQuantumToChar(p-&gt;green);
1089 *q++=ScaleQuantumToChar(p-&gt;blue);
1090 p++;
1091 }
1092 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
1093 if ((image-&gt;previous == (Image *) NULL) &&
1094 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1095 break;
1096 }
1097 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1098 if (GetNextImageInList(image) == (Image *) NULL)
1099 break;
1100 image=SyncNextImageInList(image);
1101 status=SetImageProgress(image,SaveImagesTag,scene,
1102 GetImageListLength(image));
1103 if (status == MagickFalse)
1104 break;
1105 scene++;
1106 } while (image_info-&gt;adjoin != MagickFalse);
1107 (void) CloseBlob(image);
1108 return(MagickTrue);
1109}
1110</pre>
1111</div>
1112
1113<p>To invoke the custom coder from the command line, use these commands:</p>
1114
1115<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>
1116<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>
1117
1118</div>
1119
1120<h2><a name="filters"></a>Custom Image Filters</h2>
1121<div class="doc-section">
1122
1123<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>
1124
1125<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>
1126
1127<div class="viewport">
1128<pre class="code">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1129#include &lt;stdio.h&gt;
1130#include &lt;stdlib.h&gt;
1131#include &lt;string.h&gt;
1132#include &lt;time.h&gt;
1133#include &lt;assert.h&gt;
1134#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1135#include "magick/MagickCore.h"
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1136
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1137/*
1138%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1139% %
1140% %
1141% %
1142% a n a l y z e I m a g e %
1143% %
1144% %
1145% %
1146%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1147%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1148% analyzeImage() computes the brightness and saturation mean, standard
1149% deviation, kurtosis and skewness and stores these values as attributes
1150% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1151%
1152% The format of the analyzeImage method is:
1153%
1154% unsigned long analyzeImage(Image *images,const int argc,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1155% char **argv,ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1156%
1157% A description of each parameter follows:
1158%
1159% o image: the address of a structure of type Image.
1160%
1161% o argc: Specifies a pointer to an integer describing the number of
1162% elements in the argument vector.
1163%
1164% o argv: Specifies a pointer to a text array containing the command line
1165% arguments.
1166%
1167% o exception: return any errors or warnings in this structure.
1168%
1169*/
1170ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1171 const char **argv,ExceptionInfo *exception)
1172{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1173 char
1174 text[MaxTextExtent];
1175
1176 double
1177 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1178 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1179 brightness_mean,
1180 brightness_standard_deviation,
1181 brightness_kurtosis,
1182 brightness_skewness,
1183 brightness_sum_x,
1184 brightness_sum_x2,
1185 brightness_sum_x3,
1186 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1187 hue,
1188 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1189 saturation_mean,
1190 saturation_standard_deviation,
1191 saturation_kurtosis,
1192 saturation_skewness,
1193 saturation_sum_x,
1194 saturation_sum_x2,
1195 saturation_sum_x3,
1196 saturation_sum_x4;
1197
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1198 Image
1199 *image;
1200
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1201 assert(images != (Image **) NULL);
1202 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1203 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1204 (void) argc;
1205 (void) argv;
1206 image=(*images);
1207 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1208 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1209 CacheView
1210 *image_view;
1211
1212 long
1213 y;
1214
1215 MagickBooleanType
1216 status;
1217
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1218 brightness_sum_x=0.0;
1219 brightness_sum_x2=0.0;
1220 brightness_sum_x3=0.0;
1221 brightness_sum_x4=0.0;
1222 brightness_mean=0.0;
1223 brightness_standard_deviation=0.0;
1224 brightness_kurtosis=0.0;
1225 brightness_skewness=0.0;
1226 saturation_sum_x=0.0;
1227 saturation_sum_x2=0.0;
1228 saturation_sum_x3=0.0;
1229 saturation_sum_x4=0.0;
1230 saturation_mean=0.0;
1231 saturation_standard_deviation=0.0;
1232 saturation_kurtosis=0.0;
1233 saturation_skewness=0.0;
1234 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1235 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1236 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1237#if defined(MAGICKCORE_OPENMP_SUPPORT)
1238 #pragma omp parallel for schedule(dynamic,4) shared(status)
1239#endif
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1240 for (y=0; y &lt; (long) image-&gt;rows; y++)
1241 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1242 register const PixelPacket
1243 *p;
1244
1245 register long
1246 x;
1247
1248 if (status == MagickFalse)
1249 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1250 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1251 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1252 {
1253 status=MagickFalse;
1254 continue;
1255 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1256 for (x=0; x &lt; (long) image-&gt;columns; x++)
1257 {
1258 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1259 brightness*=QuantumRange;
1260 brightness_sum_x+=brightness;
1261 brightness_sum_x2+=brightness*brightness;
1262 brightness_sum_x3+=brightness*brightness*brightness;
1263 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1264 saturation*=QuantumRange;
1265 saturation_sum_x+=saturation;
1266 saturation_sum_x2+=saturation*saturation;
1267 saturation_sum_x3+=saturation*saturation*saturation;
1268 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1269 area++;
1270 p++;
1271 }
1272 }
1273 image_view=DestroyCacheView(image_view);
1274 if (area &lt;= 0.0)
1275 break;
1276 brightness_mean=brightness_sum_x/area;
1277 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1278 (void) SetImageProperty(image,"filter:brightness:mean",text);
1279 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1280 area*brightness_sum_x/area));
1281 (void) FormatMagickString(text,MaxTextExtent,"%g",
1282 brightness_standard_deviation);
1283 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1284 if (brightness_standard_deviation != 0)
1285 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1286 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1287 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1288 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1289 brightness_standard_deviation*brightness_standard_deviation*
1290 brightness_standard_deviation)-3.0;
1291 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1292 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1293 if (brightness_standard_deviation != 0)
1294 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1295 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1296 brightness_mean)/(brightness_standard_deviation*
1297 brightness_standard_deviation*brightness_standard_deviation);
1298 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1299 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1300 saturation_mean=saturation_sum_x/area;
1301 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1302 (void) SetImageProperty(image,"filter:saturation:mean",text);
1303 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1304 area*saturation_sum_x/area));
1305 (void) FormatMagickString(text,MaxTextExtent,"%g",
1306 saturation_standard_deviation);
1307 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1308 if (saturation_standard_deviation != 0)
1309 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1310 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1311 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1312 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1313 saturation_standard_deviation*saturation_standard_deviation*
1314 saturation_standard_deviation)-3.0;
1315 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1316 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1317 if (saturation_standard_deviation != 0)
1318 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1319 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1320 saturation_mean)/(saturation_standard_deviation*
1321 saturation_standard_deviation*saturation_standard_deviation);
1322 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1323 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1324 }
1325 return(MagickImageFilterSignature);
1326}
1327</pre>
1328</div>
1329
1330<p>To invoke the custom filter from the command line, use this command:</p>
1331
1332<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/>
1333 Format: LOGO (ImageMagick Logo) <br/>
1334 Class: PseudoClass <br/>
1335 Geometry: 640x480 <br/>
1336 ... <br/>
1337 filter:brightness:kurtosis: 8.98864 <br/>
1338 filter:brightness:mean: 238.096 <br/>
1339 filter:brightness:skewness: -3.04519 <br/>
1340 filter:brightness:standard-deviation: 46.3286 <br/>
1341 filter:saturation:kurtosis: 5.9137 <br/>
1342 filter:saturation:mean: 23.4635 <br/>
1343 filter:saturation:skewness: 2.71874 <br/>
1344 filter:saturation:standard-deviation: 64.7734</span></p>
1345
1346<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>
1347
1348</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1349
1350</div>
1351
1352<div id="linkbar">
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