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165<div class="main">
166
167
168
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]169<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]170
171<div class="doc-section">
172<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>
173</div>
174
175<h2><a name="overview"></a>Architecture Overview</h2>
176<div class="doc-section">
177
178<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>
179
180<ul>
181 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
182 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
183 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
184 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
185 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
186 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
187</ul>
188
189<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>
190
191<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
192
193<ul>
194 <li>one pixel a time (e.g. pixel at location 10,3)</li>
195 <li>a single scanline (e.g. all pixels from row 4)</li>
196 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
197 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
198 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
199 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
200 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
201 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
202 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
203 <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>
204 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]205 <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]206</ul>
207
208<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>
209
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]210<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]211
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]212<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]213
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]214<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]215
216</div>
217
218<h2><a name="cache"></a>The Pixel Cache</h2>
219<div class="doc-section">
220
221<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 when you signal your intention to update any of the pixels.</p>
222
223<h3>Create the Pixel Cache</h3>
224<div class="doc-section">
225
226<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>
227
228<h4>Create an image canvas initialized to the background color:</h4>
229<p class="code">
230 image=AllocateImage(image_info);
231 if (SetImageExtent(image,640,480) == MagickFalse)
232 { /* an exception was thrown */ }
233 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
234 SetImageBackgroundColor(image);
235</p>
236
237<h4>Create an image from a JPEG image on disk:</h4>
238<p class="code"> (void) strcpy(image_info-&gt;filename,"image.jpg"):
239 image=ReadImage(image_info,exception);
240 if (image == (Image *) NULL)
241 { /* an exception was thrown */ }
242</p>
243<h4>Create an image from a memory based image:</h4>
244<p class="code">
245 image=BlobToImage(blob_info,blob,extent,exception);
246 if (image == (Image *) NULL)
247 { /* an exception was thrown */ }
248</p>
249
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]250<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]251
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]252<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]253
cristy851dbce2010-08-06 21:40:00 +0000[diff] [blame^]254<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.3-3 2010-37-35 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]255<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]256</div>
257
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]258<h3><a name="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]259<div class="doc-section">
260
261<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>
262<ul>
263 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify</li>
264 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
265 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
266 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
267</ul>
268
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]269<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]270
271<div class="viewport">
272<pre class="code">
273 long
274 x,
275 y;
276
277 const PixelPacket
278 *p;
279
280 PixelPacket
281 *q;
282
283 destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
284 if (destination == (Image *) NULL)
285 { /* an exception was thrown */ }
286 for (y=0; y &lt; (long) source-&gt;rows; y++)
287 {
288 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
289 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
290 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
291 break;
292 for (x=0; x &lt; (long) source-&gt;columns; x++)
293 {
294 q-&gt;red=90*p-&gt;red/100;
295 q-&gt;green=90*p-&gt;green/100;
296 q-&gt;blue=90*p-&gt;blue/100;
297 q-&gt;opacity=90*p-&gt;opacity/100;
298 p++;
299 q++;
300 }
301 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
302 break;
303 }
304 if (y &lt; (long) source-&gt;rows)
305 { /* an exception was thrown */ }
306</pre>
307</div>
308
309<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. Finally, use <a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p>
310
311<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>
312
313<pre class="code">
314 const IndexPacket
315 *indexes;
316
317 for (y=0; y &lt; (long) source-&gt;rows; y++)
318 {
319 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
320 if (p == (const PixelPacket *) NULL)
321 break;
322 indexes=GetVirtualIndexes(source);
323 for (x=0; x &lt; (long) source-&gt;columns; x++)
324 (void) printf("%d\n",indexes[x];
325 }
326 if (y &lt; (long) source-&gt;rows)
327 /* an exception was thrown */
328</pre>
329
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]330<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]331
332<pre class="code">
333 p=GetVirtualPixels(source,-3,3,source-&gt;columns+7,7,exception);
334</pre>
335
336<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
337</div>
338
339<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
340<div class="doc-section">
341
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]342<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]343 <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>
344
345<pre class="text">
346 background: the area surrounding the image is the background color
347 black: the area surrounding the image is black
348 checker-tile: alternate squares with image and background color
349 dither: non-random 32x32 dithered pattern
350 edge: extend the edge pixel toward infinity
351 gray: the area surrounding the image is gray
352 horizontal-tile: horizontally tile the image, background color above/below
353 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
354 mirror: mirror tile the image
355 random: choose a random pixel from the image
356 tile: tile the image (default)
357 transparent: the area surrounding the image is transparent blackness
358 vertical-tile: vertically tile the image, sides are background color
359 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
360 white: the area surrounding the image is white
361</pre>
362
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]363</div>
364
365<h3>Cache Storage and Resource Requirements</h3>
366<div class="doc-section">
367
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]368<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]369
370<dl class="doc">
371 <dt class="doc">files</dt>
372 <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>
373 <dt class="doc">area</dt>
374 <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>
375 <dt class="doc">memory</dt>
376 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
377 <dt class="doc">map</dt>
378 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
379 <dt class="doc">disk</dt>
380 <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>
381</dl>
382
383<p>To determine the current setting of these limits, use this command:</p>
384
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]385<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
386-------------------------------------------------------------------------------
387 768 12.443GB 8.6917GiB 23.178GiB 18.446744EB 8 unlimited</pre></span></p>
cristyb15553d2010-07-03 22:53:14 +0000[diff] [blame]388<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]389
390<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>
391</div>
392
393<h3>Cache Views</h3>
394<div class="doc-section">
395
396<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>
397
398<pre class="code">
399 CacheView
400 *view_1,
401 *view_2;
402
403 view_1=OpenCacheView(source);
404 view_2=OpenCacheView(source);
405 for (y=0; y &lt; (long) source-&gt;rows; y++)
406 {
407 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
408 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,exception);
409 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
410 break;
411 for (x=0; x &lt; (long) source-&gt;columns; x++)
412 {
413 /* do something with u &amp; v here */
414 }
415 }
416 view_1=CloseCacheView(view_1);
417 view_2=CloseCacheView(view_2);
418 if (y &lt; (long) source-&gt;rows)
419 { /* an exception was thrown */ }
420</pre>
421</div>
422
423<h3>Magick Persistent Cache Format</h3>
424<div class="doc-section">
425
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]426<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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]427</div>
428
429<h3>Best Practices</h3>
430<div class="doc-section">
431
432<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>
433
434<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>
435
436<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>
437
438<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>
439
440<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>
441
442<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>
443
444<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>
445
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]446<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]447
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]448<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]449
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]450<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]451
452<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>
453
454<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>
455<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>
456</div>
457
458</div>
459
460<h2><a name="stream"></a>Streaming Pixels</h2>
461<div class="doc-section">
462
463<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>
464
465<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>
466
467<pre class="code">
468static size_t StreamHandler(const Image *image,const void *pixels,
469 const size_t columns)
470{
471 /* process pixels here */
472 return(columns);
473}
474
475...
476/* invoke the pixel stream here */
477image=ReadStream(image_info,&amp;StreamHandler,exception);
478</pre>
479
480<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>
481
482</div>
483
484<h2><a name="properties"></a>Image Properties and Profiles</h2>
485<div class="doc-section">
486
487<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>
488
489<pre class="code">
490 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
491</pre>
492
493<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>
494
495<pre class="code">
496 const char
497 *comment;
498
499 (void) SetImageProperty(image,"comment","This space for rent");
500 comment=GetImageProperty(image,"comment");
501 if (comment == (const char *) NULL)
502 (void) printf("Image comment: %s\n",comment);
503</pre>
504
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]505<p>ImageMagick supports artifacts with the GetImageArtifact() and SetImageArtifact() methods. Artifacts are stealth properties that are not exported to image formats (e.g. PNG) and they do not display when identifying an image.</p>
506
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]507<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>
508
509<pre class="code">
510 StringInfo
511 *profile;
512
513 profile=AcquireStringInfo(length);
514 SetStringInfoDatum(profile,my_exif_profile);
515 (void) SetImageProfile(image,"EXIF",profile);
516 DestroyStringInfo(profile);
517 profile=GetImageProfile(image,"EXIF");
518 if (profile != (StringInfo *) NULL)
519 (void) PrintStringInfo(stdout,"EXIF",profile);
520</pre>
521
522</div>
523
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]524<h2><a name="tera-pixel"></a>Large Image Support</h2>
525<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]526<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]527
528<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]529<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]530
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]531<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]532<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>
533
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]534<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]535<p>Here we force all image pixels to disk:</p>
536
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]537<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]538<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]539
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]540<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]541
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]542<h2><a name="threads"></a>Threads of Execution</h2>
543<div class="doc-section">
544
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]545<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]546
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]547<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]548
549<div class="viewport">
550<pre class="code">
551{
552 CacheView
553 *image_view;
554
555 long
556 y;
557
558 MagickBooleanType
559 status;
560
561 status=MagickTrue;
562 image_view=AcquireCacheView(image);
563 #pragma omp parallel for schedule(dynamic,4) shared(status)
564 for (y=0; y &lt; (long) image-&gt;rows; y++)
565 {
566 register IndexPacket
567 *indexes;
568
569 register long
570 x;
571
572 register PixelPacket
573 *q;
574
575 if (status == MagickFalse)
576 continue;
577 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
578 if (q == (PixelPacket *) NULL)
579 {
580 status=MagickFalse;
581 continue;
582 }
583 indexes=GetCacheViewAuthenticIndexQueue(image_view);
584 for (x=0; x &lt; (long) image-&gt;columns; x++)
585 {
586 q-&gt;red= ...
587 q-&gt;green= ...
588 q-&gt;blue= ...
589 q-&gt;opacity= ...
590 if (indexes != (IndexPacket *) NULL)
591 indexes[x]= ...
592 q++;
593 }
594 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
595 status=MagickFalse;
596 }
597 image_view=DestroyCacheView(image_view);
598 if (status == MagickFalse)
599 perror("something went wrong");
600}
601</pre>
602</div>
603
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]604
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]605<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>
606
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]607<p><a href="../www/api/wand-view.html">MagickWand</a> support 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]608
609<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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]610</div>
611
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]612<h2><a name="distributed"></a>Heterogeneous Distributed Processing</h2>
613<div class="doc-section">
614<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>
615
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]616<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]617
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]618<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
619<p>If so, run this command to realize a significant speed-up for image convolution:</p>
620
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]621<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]622<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
623
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]624<p>Here is an example OpenCL kernel that convolves an image:</p>
625
626<div class="viewport">
627<pre class="code">
628static inline long ClampToCanvas(const long offset,const ulong range)
629{
630 if (offset &lt; 0L)
631 return(0L);
632 if (offset >= range)
633 return((long) (range-1L));
634 return(offset);
635}
636
637static inline CLQuantum ClampToQuantum(const double value)
638{
639 if (value &lt; 0.0)
640 return((CLQuantum) 0);
641 if (value >= (double) QuantumRange)
642 return((CLQuantum) QuantumRange);
643 return((CLQuantum) (value+0.5));
644}
645
646__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
647 const ulong width,const ulong height,__global CLPixelType *destination)
648{
649 const ulong columns = get_global_size(0);
650 const ulong rows = get_global_size(1);
651
652 const long x = get_global_id(0);
653 const long y = get_global_id(1);
654
655 const double scale = (1.0/QuantumRange);
656 const long mid_width = (width-1)/2;
657 const long mid_height = (height-1)/2;
658 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
659 double gamma = 0.0;
660 register ulong i = 0;
661
662 for (long v=(-mid_height); v &lt;= mid_height; v++)
663 {
664 for (long u=(-mid_width); u &lt;= mid_width; u++)
665 {
666 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,columns);
667 const double alpha=scale*(QuantumRange-source[index].w);
668 sum.x+=alpha*filter[i]*source[index].x;
669 sum.y+=alpha*filter[i]*source[index].y;
670 sum.z+=alpha*filter[i]*source[index].z;
671 sum.w+=filter[i]*source[index].w;
672 gamma+=alpha*filter[i];
673 i++;
674 }
675 }
676
677 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
678 const ulong index=y*columns+x;
679 destination[index].x=ClampToQuantum(gamma*sum.x);
680 destination[index].y=ClampToQuantum(gamma*sum.y);
681 destination[index].z=ClampToQuantum(gamma*sum.z);
682 destination[index].w=ClampToQuantum(sum.w);
683};
684</pre>
685</div>
686
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]687<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]688
689</div>
690
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]691<h2><a name="coders"></a>Custom Image Coders</h2>
692<div class="doc-section">
693
694<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>
695
696<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>
697
698<div class="viewport">
699<pre class="code">
700/*
701 Include declarations.
702*/
703#include "magick/studio.h"
704#include "magick/blob.h"
705#include "magick/blob-private.h"
706#include "magick/colorspace.h"
707#include "magick/exception.h"
708#include "magick/exception-private.h"
709#include "magick/image.h"
710#include "magick/image-private.h"
711#include "magick/list.h"
712#include "magick/magick.h"
713#include "magick/memory_.h"
714#include "magick/monitor.h"
715#include "magick/monitor-private.h"
716#include "magick/quantum-private.h"
717#include "magick/static.h"
718#include "magick/string_.h"
719#include "magick/module.h"
720
721/*
722 Forward declarations.
723*/
724static MagickBooleanType
725 WriteMGKImage(const ImageInfo *,Image *);
726
727/*
728%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
729% %
730% %
731% %
732% I s M G K %
733% %
734% %
735% %
736%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
737%
738% IsMGK() returns MagickTrue if the image format type, identified by the
739% magick string, is MGK.
740%
741% The format of the IsMGK method is:
742%
743% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
744%
745% A description of each parameter follows:
746%
747% o magick: This string is generally the first few bytes of an image file
748% or blob.
749%
750% o length: Specifies the length of the magick string.
751%
752*/
753static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
754{
755 if (length &lt; 7)
756 return(MagickFalse);
757 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
758 return(MagickTrue);
759 return(MagickFalse);
760}
761
762/*
763%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
764% %
765% %
766% %
767% R e a d M G K I m a g e %
768% %
769% %
770% %
771%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
772%
773% ReadMGKImage() reads a MGK image file and returns it. It allocates
774% the memory necessary for the new Image structure and returns a pointer to
775% the new image.
776%
777% The format of the ReadMGKImage method is:
778%
779% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
780%
781% A description of each parameter follows:
782%
783% o image_info: the image info.
784%
785% o exception: return any errors or warnings in this structure.
786%
787*/
788static Image *ReadMGKImage(const ImageInfo *image_info,
789 ExceptionInfo *exception)
790{
791 char
792 buffer[MaxTextExtent];
793
794 Image
795 *image;
796
797 long
798 y;
799
800 MagickBooleanType
801 status;
802
803 register long
804 x;
805
806 register PixelPacket
807 *q;
808
809 register unsigned char
810 *p;
811
812 ssize_t
813 count;
814
815 unsigned char
816 *pixels;
817
818 unsigned long
819 columns,
820 rows;
821
822 /*
823 Open image file.
824 */
825 assert(image_info != (const ImageInfo *) NULL);
826 assert(image_info-&gt;signature == MagickSignature);
827 if (image_info-&gt;debug != MagickFalse)
828 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
829 assert(exception != (ExceptionInfo *) NULL);
830 assert(exception-&gt;signature == MagickSignature);
831 image=AcquireImage(image_info);
832 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
833 if (status == MagickFalse)
834 {
835 image=DestroyImageList(image);
836 return((Image *) NULL);
837 }
838 /*
839 Read MGK image.
840 */
841 (void) ReadBlobString(image,buffer); /* read magic number */
842 if (IsMGK(buffer,7) == MagickFalse)
843 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
844 (void) ReadBlobString(image,buffer);
845 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
846 if (count &lt;= 0)
847 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
848 do
849 {
850 /*
851 Initialize image structure.
852 */
853 image-&gt;columns=columns;
854 image-&gt;rows=rows;
855 image-&gt;depth=8;
856 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
857 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
858 break;
859 /*
860 Convert MGK raster image to pixel packets.
861 */
862 if (SetImageExtent(image,0,0) == MagickFalse)
863 {
864 InheritException(exception,&amp;image-&gt;exception);
865 return(DestroyImageList(image));
866 }
867 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
868 if (pixels == (unsigned char *) NULL)
869 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
870 for (y=0; y &lt; (long) image-&gt;rows; y++)
871 {
872 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
873 if (count != (ssize_t) (3*image-&gt;columns))
874 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
875 p=pixels;
876 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
877 if (q == (PixelPacket *) NULL)
878 break;
879 for (x=0; x &lt; (long) image-&gt;columns; x++)
880 {
881 q-&gt;red=ScaleCharToQuantum(*p++);
882 q-&gt;green=ScaleCharToQuantum(*p++);
883 q-&gt;blue=ScaleCharToQuantum(*p++);
884 q++;
885 }
886 if (SyncAuthenticPixels(image,exception) == MagickFalse)
887 break;
888 if ((image-&gt;previous == (Image *) NULL) &&
889 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
890 break;
891 }
892 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
893 if (EOFBlob(image) != MagickFalse)
894 {
895 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
896 break;
897 }
898 /*
899 Proceed to next image.
900 */
901 if (image_info-&gt;number_scenes != 0)
902 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
903 break;
904 *buffer='\0';
905 (void) ReadBlobString(image,buffer);
906 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
907 if (count != 0)
908 {
909 /*
910 Allocate next image structure.
911 */
912 AcquireNextImage(image_info,image);
913 if (GetNextImageInList(image) == (Image *) NULL)
914 {
915 image=DestroyImageList(image);
916 return((Image *) NULL);
917 }
918 image=SyncNextImageInList(image);
919 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
920 if (status == MagickFalse)
921 break;
922 }
923 } while (count != 0);
924 (void) CloseBlob(image);
925 return(GetFirstImageInList(image));
926}
927
928/*
929%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
930% %
931% %
932% %
933% R e g i s t e r M G K I m a g e %
934% %
935% %
936% %
937%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
938%
939% RegisterMGKImage() adds attributes for the MGK image format to
940% the list of supported formats. The attributes include the image format
941% tag, a method to read and/or write the format, whether the format
942% supports the saving of more than one frame to the same file or blob,
943% whether the format supports native in-memory I/O, and a brief
944% description of the format.
945%
946% The format of the RegisterMGKImage method is:
947%
948% unsigned long RegisterMGKImage(void)
949%
950*/
951ModuleExport unsigned long RegisterMGKImage(void)
952{
953 MagickInfo
954 *entry;
955
956 entry=SetMagickInfo("MGK");
957 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
958 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
959 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
960 entry-&gt;description=ConstantString("MGK");
961 entry-&gt;module=ConstantString("MGK");
962 (void) RegisterMagickInfo(entry);
963 return(MagickImageCoderSignature);
964}
965
966/*
967%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
968% %
969% %
970% %
971% U n r e g i s t e r M G K I m a g e %
972% %
973% %
974% %
975%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
976%
977% UnregisterMGKImage() removes format registrations made by the
978% MGK module from the list of supported formats.
979%
980% The format of the UnregisterMGKImage method is:
981%
982% UnregisterMGKImage(void)
983%
984*/
985ModuleExport void UnregisterMGKImage(void)
986{
987 (void) UnregisterMagickInfo("MGK");
988}
989
990/*
991%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
992% %
993% %
994% %
995% W r i t e M G K I m a g e %
996% %
997% %
998% %
999%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1000%
1001% WriteMGKImage() writes an image to a file in red, green, and blue
1002% MGK rasterfile format.
1003%
1004% The format of the WriteMGKImage method is:
1005%
1006% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1007%
1008% A description of each parameter follows.
1009%
1010% o image_info: the image info.
1011%
1012% o image: The image.
1013%
1014*/
1015static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1016{
1017 char
1018 buffer[MaxTextExtent];
1019
1020 long
1021 y;
1022
1023 MagickBooleanType
1024 status;
1025
1026 MagickOffsetType
1027 scene;
1028
1029 register const PixelPacket
1030 *p;
1031
1032 register long
1033 x;
1034
1035 register unsigned char
1036 *q;
1037
1038 unsigned char
1039 *pixels;
1040
1041 /*
1042 Open output image file.
1043 */
1044 assert(image_info != (const ImageInfo *) NULL);
1045 assert(image_info-&gt;signature == MagickSignature);
1046 assert(image != (Image *) NULL);
1047 assert(image-&gt;signature == MagickSignature);
1048 if (image-&gt;debug != MagickFalse)
1049 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1050 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1051 if (status == MagickFalse)
1052 return(status);
1053 scene=0;
1054 do
1055 {
1056 /*
1057 Allocate memory for pixels.
1058 */
1059 if (image-&gt;colorspace != RGBColorspace)
1060 (void) SetImageColorspace(image,RGBColorspace);
1061 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1062 3UL*sizeof(*pixels));
1063 if (pixels == (unsigned char *) NULL)
1064 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1065 /*
1066 Initialize raster file header.
1067 */
1068 (void) WriteBlobString(image,"id=mgk\n");
1069 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1070 image-&gt;columns,image-&gt;rows);
1071 (void) WriteBlobString(image,buffer);
1072 for (y=0; y &lt; (long) image-&gt;rows; y++)
1073 {
1074 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1075 if (p == (const PixelPacket *) NULL)
1076 break;
1077 q=pixels;
1078 for (x=0; x &lt; (long) image-&gt;columns; x++)
1079 {
1080 *q++=ScaleQuantumToChar(p-&gt;red);
1081 *q++=ScaleQuantumToChar(p-&gt;green);
1082 *q++=ScaleQuantumToChar(p-&gt;blue);
1083 p++;
1084 }
1085 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
1086 if ((image-&gt;previous == (Image *) NULL) &&
1087 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1088 break;
1089 }
1090 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1091 if (GetNextImageInList(image) == (Image *) NULL)
1092 break;
1093 image=SyncNextImageInList(image);
1094 status=SetImageProgress(image,SaveImagesTag,scene,
1095 GetImageListLength(image));
1096 if (status == MagickFalse)
1097 break;
1098 scene++;
1099 } while (image_info-&gt;adjoin != MagickFalse);
1100 (void) CloseBlob(image);
1101 return(MagickTrue);
1102}
1103</pre>
1104</div>
1105
1106<p>To invoke the custom coder from the command line, use these commands:</p>
1107
1108<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>
1109<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>
1110
1111</div>
1112
1113<h2><a name="filters"></a>Custom Image Filters</h2>
1114<div class="doc-section">
1115
1116<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>
1117
1118<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>
1119
1120<div class="viewport">
1121<pre class="code">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1122#include &lt;stdio.h&gt;
1123#include &lt;stdlib.h&gt;
1124#include &lt;string.h&gt;
1125#include &lt;time.h&gt;
1126#include &lt;assert.h&gt;
1127#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1128#include "magick/MagickCore.h"
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1129
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1130/*
1131%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1132% %
1133% %
1134% %
1135% a n a l y z e I m a g e %
1136% %
1137% %
1138% %
1139%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1140%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1141% analyzeImage() computes the brightness and saturation mean, standard
1142% deviation, kurtosis and skewness and stores these values as attributes
1143% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1144%
1145% The format of the analyzeImage method is:
1146%
1147% unsigned long analyzeImage(Image *images,const int argc,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1148% char **argv,ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1149%
1150% A description of each parameter follows:
1151%
1152% o image: the address of a structure of type Image.
1153%
1154% o argc: Specifies a pointer to an integer describing the number of
1155% elements in the argument vector.
1156%
1157% o argv: Specifies a pointer to a text array containing the command line
1158% arguments.
1159%
1160% o exception: return any errors or warnings in this structure.
1161%
1162*/
1163ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1164 const char **argv,ExceptionInfo *exception)
1165{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1166 char
1167 text[MaxTextExtent];
1168
1169 double
1170 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1171 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1172 brightness_mean,
1173 brightness_standard_deviation,
1174 brightness_kurtosis,
1175 brightness_skewness,
1176 brightness_sum_x,
1177 brightness_sum_x2,
1178 brightness_sum_x3,
1179 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1180 hue,
1181 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1182 saturation_mean,
1183 saturation_standard_deviation,
1184 saturation_kurtosis,
1185 saturation_skewness,
1186 saturation_sum_x,
1187 saturation_sum_x2,
1188 saturation_sum_x3,
1189 saturation_sum_x4;
1190
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1191 Image
1192 *image;
1193
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1194 assert(images != (Image **) NULL);
1195 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1196 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1197 (void) argc;
1198 (void) argv;
1199 image=(*images);
1200 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1201 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1202 CacheView
1203 *image_view;
1204
1205 long
1206 y;
1207
1208 MagickBooleanType
1209 status;
1210
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1211 brightness_sum_x=0.0;
1212 brightness_sum_x2=0.0;
1213 brightness_sum_x3=0.0;
1214 brightness_sum_x4=0.0;
1215 brightness_mean=0.0;
1216 brightness_standard_deviation=0.0;
1217 brightness_kurtosis=0.0;
1218 brightness_skewness=0.0;
1219 saturation_sum_x=0.0;
1220 saturation_sum_x2=0.0;
1221 saturation_sum_x3=0.0;
1222 saturation_sum_x4=0.0;
1223 saturation_mean=0.0;
1224 saturation_standard_deviation=0.0;
1225 saturation_kurtosis=0.0;
1226 saturation_skewness=0.0;
1227 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1228 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1229 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1230#if defined(MAGICKCORE_OPENMP_SUPPORT)
1231 #pragma omp parallel for schedule(dynamic,4) shared(status)
1232#endif
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1233 for (y=0; y &lt; (long) image-&gt;rows; y++)
1234 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1235 register const PixelPacket
1236 *p;
1237
1238 register long
1239 x;
1240
1241 if (status == MagickFalse)
1242 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1243 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1244 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1245 {
1246 status=MagickFalse;
1247 continue;
1248 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1249 for (x=0; x &lt; (long) image-&gt;columns; x++)
1250 {
1251 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1252 brightness*=QuantumRange;
1253 brightness_sum_x+=brightness;
1254 brightness_sum_x2+=brightness*brightness;
1255 brightness_sum_x3+=brightness*brightness*brightness;
1256 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1257 saturation*=QuantumRange;
1258 saturation_sum_x+=saturation;
1259 saturation_sum_x2+=saturation*saturation;
1260 saturation_sum_x3+=saturation*saturation*saturation;
1261 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1262 area++;
1263 p++;
1264 }
1265 }
1266 image_view=DestroyCacheView(image_view);
1267 if (area &lt;= 0.0)
1268 break;
1269 brightness_mean=brightness_sum_x/area;
1270 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1271 (void) SetImageProperty(image,"filter:brightness:mean",text);
1272 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1273 area*brightness_sum_x/area));
1274 (void) FormatMagickString(text,MaxTextExtent,"%g",
1275 brightness_standard_deviation);
1276 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1277 if (brightness_standard_deviation != 0)
1278 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1279 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1280 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1281 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1282 brightness_standard_deviation*brightness_standard_deviation*
1283 brightness_standard_deviation)-3.0;
1284 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1285 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1286 if (brightness_standard_deviation != 0)
1287 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1288 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1289 brightness_mean)/(brightness_standard_deviation*
1290 brightness_standard_deviation*brightness_standard_deviation);
1291 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1292 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1293 saturation_mean=saturation_sum_x/area;
1294 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1295 (void) SetImageProperty(image,"filter:saturation:mean",text);
1296 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1297 area*saturation_sum_x/area));
1298 (void) FormatMagickString(text,MaxTextExtent,"%g",
1299 saturation_standard_deviation);
1300 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1301 if (saturation_standard_deviation != 0)
1302 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1303 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1304 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1305 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1306 saturation_standard_deviation*saturation_standard_deviation*
1307 saturation_standard_deviation)-3.0;
1308 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1309 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1310 if (saturation_standard_deviation != 0)
1311 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1312 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1313 saturation_mean)/(saturation_standard_deviation*
1314 saturation_standard_deviation*saturation_standard_deviation);
1315 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1316 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1317 }
1318 return(MagickImageFilterSignature);
1319}
1320</pre>
1321</div>
1322
1323<p>To invoke the custom filter from the command line, use this command:</p>
1324
1325<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/>
1326 Format: LOGO (ImageMagick Logo) <br/>
1327 Class: PseudoClass <br/>
1328 Geometry: 640x480 <br/>
1329 ... <br/>
1330 filter:brightness:kurtosis: 8.98864 <br/>
1331 filter:brightness:mean: 238.096 <br/>
1332 filter:brightness:skewness: -3.04519 <br/>
1333 filter:brightness:standard-deviation: 46.3286 <br/>
1334 filter:saturation:kurtosis: 5.9137 <br/>
1335 filter:saturation:mean: 23.4635 <br/>
1336 filter:saturation:skewness: 2.71874 <br/>
1337 filter:saturation:standard-deviation: 64.7734</span></p>
1338
1339<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>
1340
1341</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1342
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