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150
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152
153<div class="main">
154
155
156
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]157<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]158
159<div class="doc-section">
160<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>
161</div>
162
163<h2><a name="overview"></a>Architecture Overview</h2>
164<div class="doc-section">
165
166<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>
167
168<ul>
169 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
170 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
171 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
172 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
173 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
174 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
175</ul>
176
177<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>
178
179<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
180
181<ul>
182 <li>one pixel a time (e.g. pixel at location 10,3)</li>
183 <li>a single scanline (e.g. all pixels from row 4)</li>
184 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
185 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
186 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
187 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
188 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
189 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
190 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
191 <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>
192 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]193 <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]194</ul>
195
196<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>
197
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]198<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]199
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]200<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]201
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]202<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]203
204</div>
205
206<h2><a name="cache"></a>The Pixel Cache</h2>
207<div class="doc-section">
208
209<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>
210
211<h3>Create the Pixel Cache</h3>
212<div class="doc-section">
213
214<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>
215
216<h4>Create an image canvas initialized to the background color:</h4>
217<p class="code">
218 image=AllocateImage(image_info);
219 if (SetImageExtent(image,640,480) == MagickFalse)
220 { /* an exception was thrown */ }
221 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
222 SetImageBackgroundColor(image);
223</p>
224
225<h4>Create an image from a JPEG image on disk:</h4>
226<p class="code"> (void) strcpy(image_info-&gt;filename,"image.jpg"):
227 image=ReadImage(image_info,exception);
228 if (image == (Image *) NULL)
229 { /* an exception was thrown */ }
230</p>
231<h4>Create an image from a memory based image:</h4>
232<p class="code">
233 image=BlobToImage(blob_info,blob,extent,exception);
234 if (image == (Image *) NULL)
235 { /* an exception was thrown */ }
236</p>
237
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]238<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]239
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]240<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]241
cristyfe7ce342010-06-22 15:41:50 +0000[diff] [blame^]242<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.2-7 2010-74-75 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]243<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]244</div>
245
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]246<h3><a name="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]247<div class="doc-section">
248
249<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>
250<ul>
251 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify</li>
252 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
253 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
254 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
255</ul>
256
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]257<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]258
259<div class="viewport">
260<pre class="code">
261 long
262 x,
263 y;
264
265 const PixelPacket
266 *p;
267
268 PixelPacket
269 *q;
270
271 destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
272 if (destination == (Image *) NULL)
273 { /* an exception was thrown */ }
274 for (y=0; y &lt; (long) source-&gt;rows; y++)
275 {
276 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
277 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
278 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
279 break;
280 for (x=0; x &lt; (long) source-&gt;columns; x++)
281 {
282 q-&gt;red=90*p-&gt;red/100;
283 q-&gt;green=90*p-&gt;green/100;
284 q-&gt;blue=90*p-&gt;blue/100;
285 q-&gt;opacity=90*p-&gt;opacity/100;
286 p++;
287 q++;
288 }
289 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
290 break;
291 }
292 if (y &lt; (long) source-&gt;rows)
293 { /* an exception was thrown */ }
294</pre>
295</div>
296
297<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>
298
299<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>
300
301<pre class="code">
302 const IndexPacket
303 *indexes;
304
305 for (y=0; y &lt; (long) source-&gt;rows; y++)
306 {
307 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
308 if (p == (const PixelPacket *) NULL)
309 break;
310 indexes=GetVirtualIndexes(source);
311 for (x=0; x &lt; (long) source-&gt;columns; x++)
312 (void) printf("%d\n",indexes[x];
313 }
314 if (y &lt; (long) source-&gt;rows)
315 /* an exception was thrown */
316</pre>
317
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]318<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]319
320<pre class="code">
321 p=GetVirtualPixels(source,-3,3,source-&gt;columns+7,7,exception);
322</pre>
323
324<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
325</div>
326
327<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
328<div class="doc-section">
329
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]330<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]331 <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>
332
333<pre class="text">
334 background: the area surrounding the image is the background color
335 black: the area surrounding the image is black
336 checker-tile: alternate squares with image and background color
337 dither: non-random 32x32 dithered pattern
338 edge: extend the edge pixel toward infinity
339 gray: the area surrounding the image is gray
340 horizontal-tile: horizontally tile the image, background color above/below
341 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
342 mirror: mirror tile the image
343 random: choose a random pixel from the image
344 tile: tile the image (default)
345 transparent: the area surrounding the image is transparent blackness
346 vertical-tile: vertically tile the image, sides are background color
347 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
348 white: the area surrounding the image is white
349</pre>
350
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]351</div>
352
353<h3>Cache Storage and Resource Requirements</h3>
354<div class="doc-section">
355
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]356<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]357
358<dl class="doc">
359 <dt class="doc">files</dt>
360 <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>
361 <dt class="doc">area</dt>
362 <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>
363 <dt class="doc">memory</dt>
364 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
365 <dt class="doc">map</dt>
366 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
367 <dt class="doc">disk</dt>
368 <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>
369</dl>
370
371<p>To determine the current setting of these limits, use this command:</p>
372
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]373<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
374-------------------------------------------------------------------------------
375 768 12.443GB 8.6917GiB 23.178GiB 18.446744EB 8 unlimited</pre></span></p>
376<p>You can set these limits either with <a href="../www/resources.html#environment">environment variables</a>, the <a href="../www/command-line-options.html#limit">-limit</a> command line option, or 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]377
378<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>
379</div>
380
381<h3>Cache Views</h3>
382<div class="doc-section">
383
384<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>
385
386<pre class="code">
387 CacheView
388 *view_1,
389 *view_2;
390
391 view_1=OpenCacheView(source);
392 view_2=OpenCacheView(source);
393 for (y=0; y &lt; (long) source-&gt;rows; y++)
394 {
395 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
396 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,exception);
397 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
398 break;
399 for (x=0; x &lt; (long) source-&gt;columns; x++)
400 {
401 /* do something with u &amp; v here */
402 }
403 }
404 view_1=CloseCacheView(view_1);
405 view_2=CloseCacheView(view_2);
406 if (y &lt; (long) source-&gt;rows)
407 { /* an exception was thrown */ }
408</pre>
409</div>
410
411<h3>Magick Persistent Cache Format</h3>
412<div class="doc-section">
413
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]414<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]415</div>
416
417<h3>Best Practices</h3>
418<div class="doc-section">
419
420<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>
421
422<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>
423
424<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>
425
426<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>
427
428<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>
429
430<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>
431
432<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>
433
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]434<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]435
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]436<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]437
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]438<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]439
440<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>
441
442<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>
443<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>
444</div>
445
446</div>
447
448<h2><a name="stream"></a>Streaming Pixels</h2>
449<div class="doc-section">
450
451<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>
452
453<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>
454
455<pre class="code">
456static size_t StreamHandler(const Image *image,const void *pixels,
457 const size_t columns)
458{
459 /* process pixels here */
460 return(columns);
461}
462
463...
464/* invoke the pixel stream here */
465image=ReadStream(image_info,&amp;StreamHandler,exception);
466</pre>
467
468<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>
469
470</div>
471
472<h2><a name="properties"></a>Image Properties and Profiles</h2>
473<div class="doc-section">
474
475<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>
476
477<pre class="code">
478 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
479</pre>
480
481<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>
482
483<pre class="code">
484 const char
485 *comment;
486
487 (void) SetImageProperty(image,"comment","This space for rent");
488 comment=GetImageProperty(image,"comment");
489 if (comment == (const char *) NULL)
490 (void) printf("Image comment: %s\n",comment);
491</pre>
492
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]493<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>
494
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]495<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>
496
497<pre class="code">
498 StringInfo
499 *profile;
500
501 profile=AcquireStringInfo(length);
502 SetStringInfoDatum(profile,my_exif_profile);
503 (void) SetImageProfile(image,"EXIF",profile);
504 DestroyStringInfo(profile);
505 profile=GetImageProfile(image,"EXIF");
506 if (profile != (StringInfo *) NULL)
507 (void) PrintStringInfo(stdout,"EXIF",profile);
508</pre>
509
510</div>
511
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]512<h2><a name="tera-pixel"></a>Large Image Support</h2>
513<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]514<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]515
516<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]517<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]518
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]519<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]520<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>
521
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]522<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]523<p>Here we force all image pixels to disk:</p>
524
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]525<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]526<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]527
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]528<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]529
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]530<h2><a name="threads"></a>Threads of Execution</h2>
531<div class="doc-section">
532
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]533<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]534
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]535<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]536
537<div class="viewport">
538<pre class="code">
539{
540 CacheView
541 *image_view;
542
543 long
544 y;
545
546 MagickBooleanType
547 status;
548
549 status=MagickTrue;
550 image_view=AcquireCacheView(image);
551 #pragma omp parallel for schedule(dynamic,4) shared(status)
552 for (y=0; y &lt; (long) image-&gt;rows; y++)
553 {
554 register IndexPacket
555 *indexes;
556
557 register long
558 x;
559
560 register PixelPacket
561 *q;
562
563 if (status == MagickFalse)
564 continue;
565 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
566 if (q == (PixelPacket *) NULL)
567 {
568 status=MagickFalse;
569 continue;
570 }
571 indexes=GetCacheViewAuthenticIndexQueue(image_view);
572 for (x=0; x &lt; (long) image-&gt;columns; x++)
573 {
574 q-&gt;red= ...
575 q-&gt;green= ...
576 q-&gt;blue= ...
577 q-&gt;opacity= ...
578 if (indexes != (IndexPacket *) NULL)
579 indexes[x]= ...
580 q++;
581 }
582 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
583 status=MagickFalse;
584 }
585 image_view=DestroyCacheView(image_view);
586 if (status == MagickFalse)
587 perror("something went wrong");
588}
589</pre>
590</div>
591
592<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>
593
cristyfe7ce342010-06-22 15:41:50 +0000[diff] [blame^]594
595<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]596</div>
597
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]598<h2><a name="distributed"></a>Heterogeneous Distributed Processing</h2>
599<div class="doc-section">
600<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>
601
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]602<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]603
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]604<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
605<p>If so, run this command to realize a significant speed-up for image convolution:</p>
606
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]607<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]608<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
609
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]610<p>Here is an example OpenCL kernel that convolves an image:</p>
611
612<div class="viewport">
613<pre class="code">
614static inline long ClampToCanvas(const long offset,const ulong range)
615{
616 if (offset &lt; 0L)
617 return(0L);
618 if (offset >= range)
619 return((long) (range-1L));
620 return(offset);
621}
622
623static inline CLQuantum ClampToQuantum(const double value)
624{
625 if (value &lt; 0.0)
626 return((CLQuantum) 0);
627 if (value >= (double) QuantumRange)
628 return((CLQuantum) QuantumRange);
629 return((CLQuantum) (value+0.5));
630}
631
632__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
633 const ulong width,const ulong height,__global CLPixelType *destination)
634{
635 const ulong columns = get_global_size(0);
636 const ulong rows = get_global_size(1);
637
638 const long x = get_global_id(0);
639 const long y = get_global_id(1);
640
641 const double scale = (1.0/QuantumRange);
642 const long mid_width = (width-1)/2;
643 const long mid_height = (height-1)/2;
644 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
645 double gamma = 0.0;
646 register ulong i = 0;
647
648 for (long v=(-mid_height); v &lt;= mid_height; v++)
649 {
650 for (long u=(-mid_width); u &lt;= mid_width; u++)
651 {
652 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,columns);
653 const double alpha=scale*(QuantumRange-source[index].w);
654 sum.x+=alpha*filter[i]*source[index].x;
655 sum.y+=alpha*filter[i]*source[index].y;
656 sum.z+=alpha*filter[i]*source[index].z;
657 sum.w+=filter[i]*source[index].w;
658 gamma+=alpha*filter[i];
659 i++;
660 }
661 }
662
663 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
664 const ulong index=y*columns+x;
665 destination[index].x=ClampToQuantum(gamma*sum.x);
666 destination[index].y=ClampToQuantum(gamma*sum.y);
667 destination[index].z=ClampToQuantum(gamma*sum.z);
668 destination[index].w=ClampToQuantum(sum.w);
669};
670</pre>
671</div>
672
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]673<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]674
675</div>
676
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]677<h2><a name="coders"></a>Custom Image Coders</h2>
678<div class="doc-section">
679
680<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>
681
682<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>
683
684<div class="viewport">
685<pre class="code">
686/*
687 Include declarations.
688*/
689#include "magick/studio.h"
690#include "magick/blob.h"
691#include "magick/blob-private.h"
692#include "magick/colorspace.h"
693#include "magick/exception.h"
694#include "magick/exception-private.h"
695#include "magick/image.h"
696#include "magick/image-private.h"
697#include "magick/list.h"
698#include "magick/magick.h"
699#include "magick/memory_.h"
700#include "magick/monitor.h"
701#include "magick/monitor-private.h"
702#include "magick/quantum-private.h"
703#include "magick/static.h"
704#include "magick/string_.h"
705#include "magick/module.h"
706
707/*
708 Forward declarations.
709*/
710static MagickBooleanType
711 WriteMGKImage(const ImageInfo *,Image *);
712
713/*
714%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
715% %
716% %
717% %
718% I s M G K %
719% %
720% %
721% %
722%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
723%
724% IsMGK() returns MagickTrue if the image format type, identified by the
725% magick string, is MGK.
726%
727% The format of the IsMGK method is:
728%
729% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
730%
731% A description of each parameter follows:
732%
733% o magick: This string is generally the first few bytes of an image file
734% or blob.
735%
736% o length: Specifies the length of the magick string.
737%
738*/
739static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
740{
741 if (length &lt; 7)
742 return(MagickFalse);
743 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
744 return(MagickTrue);
745 return(MagickFalse);
746}
747
748/*
749%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
750% %
751% %
752% %
753% R e a d M G K I m a g e %
754% %
755% %
756% %
757%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
758%
759% ReadMGKImage() reads a MGK image file and returns it. It allocates
760% the memory necessary for the new Image structure and returns a pointer to
761% the new image.
762%
763% The format of the ReadMGKImage method is:
764%
765% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
766%
767% A description of each parameter follows:
768%
769% o image_info: the image info.
770%
771% o exception: return any errors or warnings in this structure.
772%
773*/
774static Image *ReadMGKImage(const ImageInfo *image_info,
775 ExceptionInfo *exception)
776{
777 char
778 buffer[MaxTextExtent];
779
780 Image
781 *image;
782
783 long
784 y;
785
786 MagickBooleanType
787 status;
788
789 register long
790 x;
791
792 register PixelPacket
793 *q;
794
795 register unsigned char
796 *p;
797
798 ssize_t
799 count;
800
801 unsigned char
802 *pixels;
803
804 unsigned long
805 columns,
806 rows;
807
808 /*
809 Open image file.
810 */
811 assert(image_info != (const ImageInfo *) NULL);
812 assert(image_info-&gt;signature == MagickSignature);
813 if (image_info-&gt;debug != MagickFalse)
814 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
815 assert(exception != (ExceptionInfo *) NULL);
816 assert(exception-&gt;signature == MagickSignature);
817 image=AcquireImage(image_info);
818 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
819 if (status == MagickFalse)
820 {
821 image=DestroyImageList(image);
822 return((Image *) NULL);
823 }
824 /*
825 Read MGK image.
826 */
827 (void) ReadBlobString(image,buffer); /* read magic number */
828 if (IsMGK(buffer,7) == MagickFalse)
829 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
830 (void) ReadBlobString(image,buffer);
831 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
832 if (count &lt;= 0)
833 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
834 do
835 {
836 /*
837 Initialize image structure.
838 */
839 image-&gt;columns=columns;
840 image-&gt;rows=rows;
841 image-&gt;depth=8;
842 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
843 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
844 break;
845 /*
846 Convert MGK raster image to pixel packets.
847 */
848 if (SetImageExtent(image,0,0) == MagickFalse)
849 {
850 InheritException(exception,&amp;image-&gt;exception);
851 return(DestroyImageList(image));
852 }
853 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
854 if (pixels == (unsigned char *) NULL)
855 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
856 for (y=0; y &lt; (long) image-&gt;rows; y++)
857 {
858 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
859 if (count != (ssize_t) (3*image-&gt;columns))
860 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
861 p=pixels;
862 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
863 if (q == (PixelPacket *) NULL)
864 break;
865 for (x=0; x &lt; (long) image-&gt;columns; x++)
866 {
867 q-&gt;red=ScaleCharToQuantum(*p++);
868 q-&gt;green=ScaleCharToQuantum(*p++);
869 q-&gt;blue=ScaleCharToQuantum(*p++);
870 q++;
871 }
872 if (SyncAuthenticPixels(image,exception) == MagickFalse)
873 break;
874 if ((image-&gt;previous == (Image *) NULL) &&
875 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
876 break;
877 }
878 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
879 if (EOFBlob(image) != MagickFalse)
880 {
881 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
882 break;
883 }
884 /*
885 Proceed to next image.
886 */
887 if (image_info-&gt;number_scenes != 0)
888 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
889 break;
890 *buffer='\0';
891 (void) ReadBlobString(image,buffer);
892 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
893 if (count != 0)
894 {
895 /*
896 Allocate next image structure.
897 */
898 AcquireNextImage(image_info,image);
899 if (GetNextImageInList(image) == (Image *) NULL)
900 {
901 image=DestroyImageList(image);
902 return((Image *) NULL);
903 }
904 image=SyncNextImageInList(image);
905 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
906 if (status == MagickFalse)
907 break;
908 }
909 } while (count != 0);
910 (void) CloseBlob(image);
911 return(GetFirstImageInList(image));
912}
913
914/*
915%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
916% %
917% %
918% %
919% R e g i s t e r M G K I m a g e %
920% %
921% %
922% %
923%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
924%
925% RegisterMGKImage() adds attributes for the MGK image format to
926% the list of supported formats. The attributes include the image format
927% tag, a method to read and/or write the format, whether the format
928% supports the saving of more than one frame to the same file or blob,
929% whether the format supports native in-memory I/O, and a brief
930% description of the format.
931%
932% The format of the RegisterMGKImage method is:
933%
934% unsigned long RegisterMGKImage(void)
935%
936*/
937ModuleExport unsigned long RegisterMGKImage(void)
938{
939 MagickInfo
940 *entry;
941
942 entry=SetMagickInfo("MGK");
943 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
944 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
945 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
946 entry-&gt;description=ConstantString("MGK");
947 entry-&gt;module=ConstantString("MGK");
948 (void) RegisterMagickInfo(entry);
949 return(MagickImageCoderSignature);
950}
951
952/*
953%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
954% %
955% %
956% %
957% U n r e g i s t e r M G K I m a g e %
958% %
959% %
960% %
961%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
962%
963% UnregisterMGKImage() removes format registrations made by the
964% MGK module from the list of supported formats.
965%
966% The format of the UnregisterMGKImage method is:
967%
968% UnregisterMGKImage(void)
969%
970*/
971ModuleExport void UnregisterMGKImage(void)
972{
973 (void) UnregisterMagickInfo("MGK");
974}
975
976/*
977%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
978% %
979% %
980% %
981% W r i t e M G K I m a g e %
982% %
983% %
984% %
985%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
986%
987% WriteMGKImage() writes an image to a file in red, green, and blue
988% MGK rasterfile format.
989%
990% The format of the WriteMGKImage method is:
991%
992% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
993%
994% A description of each parameter follows.
995%
996% o image_info: the image info.
997%
998% o image: The image.
999%
1000*/
1001static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1002{
1003 char
1004 buffer[MaxTextExtent];
1005
1006 long
1007 y;
1008
1009 MagickBooleanType
1010 status;
1011
1012 MagickOffsetType
1013 scene;
1014
1015 register const PixelPacket
1016 *p;
1017
1018 register long
1019 x;
1020
1021 register unsigned char
1022 *q;
1023
1024 unsigned char
1025 *pixels;
1026
1027 /*
1028 Open output image file.
1029 */
1030 assert(image_info != (const ImageInfo *) NULL);
1031 assert(image_info-&gt;signature == MagickSignature);
1032 assert(image != (Image *) NULL);
1033 assert(image-&gt;signature == MagickSignature);
1034 if (image-&gt;debug != MagickFalse)
1035 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1036 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1037 if (status == MagickFalse)
1038 return(status);
1039 scene=0;
1040 do
1041 {
1042 /*
1043 Allocate memory for pixels.
1044 */
1045 if (image-&gt;colorspace != RGBColorspace)
1046 (void) SetImageColorspace(image,RGBColorspace);
1047 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1048 3UL*sizeof(*pixels));
1049 if (pixels == (unsigned char *) NULL)
1050 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1051 /*
1052 Initialize raster file header.
1053 */
1054 (void) WriteBlobString(image,"id=mgk\n");
1055 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1056 image-&gt;columns,image-&gt;rows);
1057 (void) WriteBlobString(image,buffer);
1058 for (y=0; y &lt; (long) image-&gt;rows; y++)
1059 {
1060 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1061 if (p == (const PixelPacket *) NULL)
1062 break;
1063 q=pixels;
1064 for (x=0; x &lt; (long) image-&gt;columns; x++)
1065 {
1066 *q++=ScaleQuantumToChar(p-&gt;red);
1067 *q++=ScaleQuantumToChar(p-&gt;green);
1068 *q++=ScaleQuantumToChar(p-&gt;blue);
1069 p++;
1070 }
1071 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
1072 if ((image-&gt;previous == (Image *) NULL) &&
1073 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1074 break;
1075 }
1076 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1077 if (GetNextImageInList(image) == (Image *) NULL)
1078 break;
1079 image=SyncNextImageInList(image);
1080 status=SetImageProgress(image,SaveImagesTag,scene,
1081 GetImageListLength(image));
1082 if (status == MagickFalse)
1083 break;
1084 scene++;
1085 } while (image_info-&gt;adjoin != MagickFalse);
1086 (void) CloseBlob(image);
1087 return(MagickTrue);
1088}
1089</pre>
1090</div>
1091
1092<p>To invoke the custom coder from the command line, use these commands:</p>
1093
1094<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>
1095<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>
1096
1097</div>
1098
1099<h2><a name="filters"></a>Custom Image Filters</h2>
1100<div class="doc-section">
1101
1102<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>
1103
1104<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>
1105
1106<div class="viewport">
1107<pre class="code">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1108#include &lt;stdio.h&gt;
1109#include &lt;stdlib.h&gt;
1110#include &lt;string.h&gt;
1111#include &lt;time.h&gt;
1112#include &lt;assert.h&gt;
1113#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1114#include "magick/MagickCore.h"
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1115
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1116/*
1117%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1118% %
1119% %
1120% %
1121% a n a l y z e I m a g e %
1122% %
1123% %
1124% %
1125%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1126%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1127% analyzeImage() computes the brightness and saturation mean, standard
1128% deviation, kurtosis and skewness and stores these values as attributes
1129% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1130%
1131% The format of the analyzeImage method is:
1132%
1133% unsigned long analyzeImage(Image *images,const int argc,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1134% char **argv,ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1135%
1136% A description of each parameter follows:
1137%
1138% o image: the address of a structure of type Image.
1139%
1140% o argc: Specifies a pointer to an integer describing the number of
1141% elements in the argument vector.
1142%
1143% o argv: Specifies a pointer to a text array containing the command line
1144% arguments.
1145%
1146% o exception: return any errors or warnings in this structure.
1147%
1148*/
1149ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1150 const char **argv,ExceptionInfo *exception)
1151{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1152 char
1153 text[MaxTextExtent];
1154
1155 double
1156 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1157 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1158 brightness_mean,
1159 brightness_standard_deviation,
1160 brightness_kurtosis,
1161 brightness_skewness,
1162 brightness_sum_x,
1163 brightness_sum_x2,
1164 brightness_sum_x3,
1165 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1166 hue,
1167 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1168 saturation_mean,
1169 saturation_standard_deviation,
1170 saturation_kurtosis,
1171 saturation_skewness,
1172 saturation_sum_x,
1173 saturation_sum_x2,
1174 saturation_sum_x3,
1175 saturation_sum_x4;
1176
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1177 Image
1178 *image;
1179
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1180 assert(images != (Image **) NULL);
1181 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1182 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1183 (void) argc;
1184 (void) argv;
1185 image=(*images);
1186 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1187 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1188 CacheView
1189 *image_view;
1190
1191 long
1192 y;
1193
1194 MagickBooleanType
1195 status;
1196
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1197 brightness_sum_x=0.0;
1198 brightness_sum_x2=0.0;
1199 brightness_sum_x3=0.0;
1200 brightness_sum_x4=0.0;
1201 brightness_mean=0.0;
1202 brightness_standard_deviation=0.0;
1203 brightness_kurtosis=0.0;
1204 brightness_skewness=0.0;
1205 saturation_sum_x=0.0;
1206 saturation_sum_x2=0.0;
1207 saturation_sum_x3=0.0;
1208 saturation_sum_x4=0.0;
1209 saturation_mean=0.0;
1210 saturation_standard_deviation=0.0;
1211 saturation_kurtosis=0.0;
1212 saturation_skewness=0.0;
1213 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1214 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1215 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1216#if defined(MAGICKCORE_OPENMP_SUPPORT)
1217 #pragma omp parallel for schedule(dynamic,4) shared(status)
1218#endif
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1219 for (y=0; y &lt; (long) image-&gt;rows; y++)
1220 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1221 register const PixelPacket
1222 *p;
1223
1224 register long
1225 x;
1226
1227 if (status == MagickFalse)
1228 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1229 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1230 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1231 {
1232 status=MagickFalse;
1233 continue;
1234 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1235 for (x=0; x &lt; (long) image-&gt;columns; x++)
1236 {
1237 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1238 brightness*=QuantumRange;
1239 brightness_sum_x+=brightness;
1240 brightness_sum_x2+=brightness*brightness;
1241 brightness_sum_x3+=brightness*brightness*brightness;
1242 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1243 saturation*=QuantumRange;
1244 saturation_sum_x+=saturation;
1245 saturation_sum_x2+=saturation*saturation;
1246 saturation_sum_x3+=saturation*saturation*saturation;
1247 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1248 area++;
1249 p++;
1250 }
1251 }
1252 image_view=DestroyCacheView(image_view);
1253 if (area &lt;= 0.0)
1254 break;
1255 brightness_mean=brightness_sum_x/area;
1256 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1257 (void) SetImageProperty(image,"filter:brightness:mean",text);
1258 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1259 area*brightness_sum_x/area));
1260 (void) FormatMagickString(text,MaxTextExtent,"%g",
1261 brightness_standard_deviation);
1262 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1263 if (brightness_standard_deviation != 0)
1264 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1265 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1266 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1267 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1268 brightness_standard_deviation*brightness_standard_deviation*
1269 brightness_standard_deviation)-3.0;
1270 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1271 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1272 if (brightness_standard_deviation != 0)
1273 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1274 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1275 brightness_mean)/(brightness_standard_deviation*
1276 brightness_standard_deviation*brightness_standard_deviation);
1277 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1278 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1279 saturation_mean=saturation_sum_x/area;
1280 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1281 (void) SetImageProperty(image,"filter:saturation:mean",text);
1282 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1283 area*saturation_sum_x/area));
1284 (void) FormatMagickString(text,MaxTextExtent,"%g",
1285 saturation_standard_deviation);
1286 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1287 if (saturation_standard_deviation != 0)
1288 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1289 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1290 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1291 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1292 saturation_standard_deviation*saturation_standard_deviation*
1293 saturation_standard_deviation)-3.0;
1294 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1295 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1296 if (saturation_standard_deviation != 0)
1297 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1298 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1299 saturation_mean)/(saturation_standard_deviation*
1300 saturation_standard_deviation*saturation_standard_deviation);
1301 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1302 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1303 }
1304 return(MagickImageFilterSignature);
1305}
1306</pre>
1307</div>
1308
1309<p>To invoke the custom filter from the command line, use this command:</p>
1310
1311<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/>
1312 Format: LOGO (ImageMagick Logo) <br/>
1313 Class: PseudoClass <br/>
1314 Geometry: 640x480 <br/>
1315 ... <br/>
1316 filter:brightness:kurtosis: 8.98864 <br/>
1317 filter:brightness:mean: 238.096 <br/>
1318 filter:brightness:skewness: -3.04519 <br/>
1319 filter:brightness:standard-deviation: 46.3286 <br/>
1320 filter:saturation:kurtosis: 5.9137 <br/>
1321 filter:saturation:mean: 23.4635 <br/>
1322 filter:saturation:skewness: 2.71874 <br/>
1323 filter:saturation:standard-deviation: 64.7734</span></p>
1324
1325<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>
1326
1327</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1328
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