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164
165
166
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]167<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]168
169<div class="doc-section">
170<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>
171</div>
172
173<h2><a name="overview"></a>Architecture Overview</h2>
174<div class="doc-section">
175
176<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>
177
178<ul>
179 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
180 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
181 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
182 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
183 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
184 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
185</ul>
186
187<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>
188
189<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
190
191<ul>
192 <li>one pixel a time (e.g. pixel at location 10,3)</li>
193 <li>a single scanline (e.g. all pixels from row 4)</li>
194 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
195 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
196 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
197 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
198 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
199 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
200 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
201 <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>
202 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]203 <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]204</ul>
205
206<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>
207
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]208<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]209
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]210<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]211
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]212<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]213
214</div>
215
216<h2><a name="cache"></a>The Pixel Cache</h2>
217<div class="doc-section">
218
219<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>
220
221<h3>Create the Pixel Cache</h3>
222<div class="doc-section">
223
224<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>
225
226<h4>Create an image canvas initialized to the background color:</h4>
227<p class="code">
228 image=AllocateImage(image_info);
229 if (SetImageExtent(image,640,480) == MagickFalse)
230 { /* an exception was thrown */ }
231 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
232 SetImageBackgroundColor(image);
233</p>
234
235<h4>Create an image from a JPEG image on disk:</h4>
236<p class="code"> (void) strcpy(image_info-&gt;filename,"image.jpg"):
237 image=ReadImage(image_info,exception);
238 if (image == (Image *) NULL)
239 { /* an exception was thrown */ }
240</p>
241<h4>Create an image from a memory based image:</h4>
242<p class="code">
243 image=BlobToImage(blob_info,blob,extent,exception);
244 if (image == (Image *) NULL)
245 { /* an exception was thrown */ }
246</p>
247
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]248<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]249
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]250<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]251
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame^]252<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.3-1 2010-17-15 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]253<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]254</div>
255
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]256<h3><a name="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]257<div class="doc-section">
258
259<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>
260<ul>
261 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify</li>
262 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
263 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
264 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
265</ul>
266
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]267<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]268
269<div class="viewport">
270<pre class="code">
271 long
272 x,
273 y;
274
275 const PixelPacket
276 *p;
277
278 PixelPacket
279 *q;
280
281 destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
282 if (destination == (Image *) NULL)
283 { /* an exception was thrown */ }
284 for (y=0; y &lt; (long) source-&gt;rows; y++)
285 {
286 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
287 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
288 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
289 break;
290 for (x=0; x &lt; (long) source-&gt;columns; x++)
291 {
292 q-&gt;red=90*p-&gt;red/100;
293 q-&gt;green=90*p-&gt;green/100;
294 q-&gt;blue=90*p-&gt;blue/100;
295 q-&gt;opacity=90*p-&gt;opacity/100;
296 p++;
297 q++;
298 }
299 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
300 break;
301 }
302 if (y &lt; (long) source-&gt;rows)
303 { /* an exception was thrown */ }
304</pre>
305</div>
306
307<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>
308
309<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>
310
311<pre class="code">
312 const IndexPacket
313 *indexes;
314
315 for (y=0; y &lt; (long) source-&gt;rows; y++)
316 {
317 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
318 if (p == (const PixelPacket *) NULL)
319 break;
320 indexes=GetVirtualIndexes(source);
321 for (x=0; x &lt; (long) source-&gt;columns; x++)
322 (void) printf("%d\n",indexes[x];
323 }
324 if (y &lt; (long) source-&gt;rows)
325 /* an exception was thrown */
326</pre>
327
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]328<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]329
330<pre class="code">
331 p=GetVirtualPixels(source,-3,3,source-&gt;columns+7,7,exception);
332</pre>
333
334<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
335</div>
336
337<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
338<div class="doc-section">
339
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]340<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]341 <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>
342
343<pre class="text">
344 background: the area surrounding the image is the background color
345 black: the area surrounding the image is black
346 checker-tile: alternate squares with image and background color
347 dither: non-random 32x32 dithered pattern
348 edge: extend the edge pixel toward infinity
349 gray: the area surrounding the image is gray
350 horizontal-tile: horizontally tile the image, background color above/below
351 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
352 mirror: mirror tile the image
353 random: choose a random pixel from the image
354 tile: tile the image (default)
355 transparent: the area surrounding the image is transparent blackness
356 vertical-tile: vertically tile the image, sides are background color
357 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
358 white: the area surrounding the image is white
359</pre>
360
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]361</div>
362
363<h3>Cache Storage and Resource Requirements</h3>
364<div class="doc-section">
365
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]366<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]367
368<dl class="doc">
369 <dt class="doc">files</dt>
370 <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>
371 <dt class="doc">area</dt>
372 <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>
373 <dt class="doc">memory</dt>
374 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
375 <dt class="doc">map</dt>
376 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
377 <dt class="doc">disk</dt>
378 <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>
379</dl>
380
381<p>To determine the current setting of these limits, use this command:</p>
382
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]383<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
384-------------------------------------------------------------------------------
385 768 12.443GB 8.6917GiB 23.178GiB 18.446744EB 8 unlimited</pre></span></p>
cristyb15553d2010-07-03 22:53:14 +0000[diff] [blame]386<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]387
388<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>
389</div>
390
391<h3>Cache Views</h3>
392<div class="doc-section">
393
394<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>
395
396<pre class="code">
397 CacheView
398 *view_1,
399 *view_2;
400
401 view_1=OpenCacheView(source);
402 view_2=OpenCacheView(source);
403 for (y=0; y &lt; (long) source-&gt;rows; y++)
404 {
405 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
406 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,exception);
407 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
408 break;
409 for (x=0; x &lt; (long) source-&gt;columns; x++)
410 {
411 /* do something with u &amp; v here */
412 }
413 }
414 view_1=CloseCacheView(view_1);
415 view_2=CloseCacheView(view_2);
416 if (y &lt; (long) source-&gt;rows)
417 { /* an exception was thrown */ }
418</pre>
419</div>
420
421<h3>Magick Persistent Cache Format</h3>
422<div class="doc-section">
423
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]424<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]425</div>
426
427<h3>Best Practices</h3>
428<div class="doc-section">
429
430<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>
431
432<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>
433
434<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>
435
436<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>
437
438<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>
439
440<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>
441
442<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>
443
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]444<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]445
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]446<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]447
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]448<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]449
450<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>
451
452<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>
453<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>
454</div>
455
456</div>
457
458<h2><a name="stream"></a>Streaming Pixels</h2>
459<div class="doc-section">
460
461<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>
462
463<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>
464
465<pre class="code">
466static size_t StreamHandler(const Image *image,const void *pixels,
467 const size_t columns)
468{
469 /* process pixels here */
470 return(columns);
471}
472
473...
474/* invoke the pixel stream here */
475image=ReadStream(image_info,&amp;StreamHandler,exception);
476</pre>
477
478<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>
479
480</div>
481
482<h2><a name="properties"></a>Image Properties and Profiles</h2>
483<div class="doc-section">
484
485<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>
486
487<pre class="code">
488 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
489</pre>
490
491<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>
492
493<pre class="code">
494 const char
495 *comment;
496
497 (void) SetImageProperty(image,"comment","This space for rent");
498 comment=GetImageProperty(image,"comment");
499 if (comment == (const char *) NULL)
500 (void) printf("Image comment: %s\n",comment);
501</pre>
502
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]503<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>
504
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]505<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>
506
507<pre class="code">
508 StringInfo
509 *profile;
510
511 profile=AcquireStringInfo(length);
512 SetStringInfoDatum(profile,my_exif_profile);
513 (void) SetImageProfile(image,"EXIF",profile);
514 DestroyStringInfo(profile);
515 profile=GetImageProfile(image,"EXIF");
516 if (profile != (StringInfo *) NULL)
517 (void) PrintStringInfo(stdout,"EXIF",profile);
518</pre>
519
520</div>
521
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]522<h2><a name="tera-pixel"></a>Large Image Support</h2>
523<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]524<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]525
526<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]527<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]528
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]529<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]530<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>
531
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]532<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]533<p>Here we force all image pixels to disk:</p>
534
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]535<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]536<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]537
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]538<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]539
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]540<h2><a name="threads"></a>Threads of Execution</h2>
541<div class="doc-section">
542
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]543<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]544
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]545<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]546
547<div class="viewport">
548<pre class="code">
549{
550 CacheView
551 *image_view;
552
553 long
554 y;
555
556 MagickBooleanType
557 status;
558
559 status=MagickTrue;
560 image_view=AcquireCacheView(image);
561 #pragma omp parallel for schedule(dynamic,4) shared(status)
562 for (y=0; y &lt; (long) image-&gt;rows; y++)
563 {
564 register IndexPacket
565 *indexes;
566
567 register long
568 x;
569
570 register PixelPacket
571 *q;
572
573 if (status == MagickFalse)
574 continue;
575 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
576 if (q == (PixelPacket *) NULL)
577 {
578 status=MagickFalse;
579 continue;
580 }
581 indexes=GetCacheViewAuthenticIndexQueue(image_view);
582 for (x=0; x &lt; (long) image-&gt;columns; x++)
583 {
584 q-&gt;red= ...
585 q-&gt;green= ...
586 q-&gt;blue= ...
587 q-&gt;opacity= ...
588 if (indexes != (IndexPacket *) NULL)
589 indexes[x]= ...
590 q++;
591 }
592 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
593 status=MagickFalse;
594 }
595 image_view=DestroyCacheView(image_view);
596 if (status == MagickFalse)
597 perror("something went wrong");
598}
599</pre>
600</div>
601
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]602
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]603<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>
604
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]605<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]606
607<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]608</div>
609
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]610<h2><a name="distributed"></a>Heterogeneous Distributed Processing</h2>
611<div class="doc-section">
612<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>
613
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]614<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]615
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]616<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
617<p>If so, run this command to realize a significant speed-up for image convolution:</p>
618
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]619<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]620<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
621
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]622<p>Here is an example OpenCL kernel that convolves an image:</p>
623
624<div class="viewport">
625<pre class="code">
626static inline long ClampToCanvas(const long offset,const ulong range)
627{
628 if (offset &lt; 0L)
629 return(0L);
630 if (offset >= range)
631 return((long) (range-1L));
632 return(offset);
633}
634
635static inline CLQuantum ClampToQuantum(const double value)
636{
637 if (value &lt; 0.0)
638 return((CLQuantum) 0);
639 if (value >= (double) QuantumRange)
640 return((CLQuantum) QuantumRange);
641 return((CLQuantum) (value+0.5));
642}
643
644__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
645 const ulong width,const ulong height,__global CLPixelType *destination)
646{
647 const ulong columns = get_global_size(0);
648 const ulong rows = get_global_size(1);
649
650 const long x = get_global_id(0);
651 const long y = get_global_id(1);
652
653 const double scale = (1.0/QuantumRange);
654 const long mid_width = (width-1)/2;
655 const long mid_height = (height-1)/2;
656 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
657 double gamma = 0.0;
658 register ulong i = 0;
659
660 for (long v=(-mid_height); v &lt;= mid_height; v++)
661 {
662 for (long u=(-mid_width); u &lt;= mid_width; u++)
663 {
664 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,columns);
665 const double alpha=scale*(QuantumRange-source[index].w);
666 sum.x+=alpha*filter[i]*source[index].x;
667 sum.y+=alpha*filter[i]*source[index].y;
668 sum.z+=alpha*filter[i]*source[index].z;
669 sum.w+=filter[i]*source[index].w;
670 gamma+=alpha*filter[i];
671 i++;
672 }
673 }
674
675 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
676 const ulong index=y*columns+x;
677 destination[index].x=ClampToQuantum(gamma*sum.x);
678 destination[index].y=ClampToQuantum(gamma*sum.y);
679 destination[index].z=ClampToQuantum(gamma*sum.z);
680 destination[index].w=ClampToQuantum(sum.w);
681};
682</pre>
683</div>
684
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]685<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]686
687</div>
688
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]689<h2><a name="coders"></a>Custom Image Coders</h2>
690<div class="doc-section">
691
692<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>
693
694<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>
695
696<div class="viewport">
697<pre class="code">
698/*
699 Include declarations.
700*/
701#include "magick/studio.h"
702#include "magick/blob.h"
703#include "magick/blob-private.h"
704#include "magick/colorspace.h"
705#include "magick/exception.h"
706#include "magick/exception-private.h"
707#include "magick/image.h"
708#include "magick/image-private.h"
709#include "magick/list.h"
710#include "magick/magick.h"
711#include "magick/memory_.h"
712#include "magick/monitor.h"
713#include "magick/monitor-private.h"
714#include "magick/quantum-private.h"
715#include "magick/static.h"
716#include "magick/string_.h"
717#include "magick/module.h"
718
719/*
720 Forward declarations.
721*/
722static MagickBooleanType
723 WriteMGKImage(const ImageInfo *,Image *);
724
725/*
726%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
727% %
728% %
729% %
730% I s M G K %
731% %
732% %
733% %
734%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
735%
736% IsMGK() returns MagickTrue if the image format type, identified by the
737% magick string, is MGK.
738%
739% The format of the IsMGK method is:
740%
741% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
742%
743% A description of each parameter follows:
744%
745% o magick: This string is generally the first few bytes of an image file
746% or blob.
747%
748% o length: Specifies the length of the magick string.
749%
750*/
751static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
752{
753 if (length &lt; 7)
754 return(MagickFalse);
755 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
756 return(MagickTrue);
757 return(MagickFalse);
758}
759
760/*
761%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
762% %
763% %
764% %
765% R e a d M G K I m a g e %
766% %
767% %
768% %
769%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
770%
771% ReadMGKImage() reads a MGK image file and returns it. It allocates
772% the memory necessary for the new Image structure and returns a pointer to
773% the new image.
774%
775% The format of the ReadMGKImage method is:
776%
777% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
778%
779% A description of each parameter follows:
780%
781% o image_info: the image info.
782%
783% o exception: return any errors or warnings in this structure.
784%
785*/
786static Image *ReadMGKImage(const ImageInfo *image_info,
787 ExceptionInfo *exception)
788{
789 char
790 buffer[MaxTextExtent];
791
792 Image
793 *image;
794
795 long
796 y;
797
798 MagickBooleanType
799 status;
800
801 register long
802 x;
803
804 register PixelPacket
805 *q;
806
807 register unsigned char
808 *p;
809
810 ssize_t
811 count;
812
813 unsigned char
814 *pixels;
815
816 unsigned long
817 columns,
818 rows;
819
820 /*
821 Open image file.
822 */
823 assert(image_info != (const ImageInfo *) NULL);
824 assert(image_info-&gt;signature == MagickSignature);
825 if (image_info-&gt;debug != MagickFalse)
826 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
827 assert(exception != (ExceptionInfo *) NULL);
828 assert(exception-&gt;signature == MagickSignature);
829 image=AcquireImage(image_info);
830 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
831 if (status == MagickFalse)
832 {
833 image=DestroyImageList(image);
834 return((Image *) NULL);
835 }
836 /*
837 Read MGK image.
838 */
839 (void) ReadBlobString(image,buffer); /* read magic number */
840 if (IsMGK(buffer,7) == MagickFalse)
841 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
842 (void) ReadBlobString(image,buffer);
843 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
844 if (count &lt;= 0)
845 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
846 do
847 {
848 /*
849 Initialize image structure.
850 */
851 image-&gt;columns=columns;
852 image-&gt;rows=rows;
853 image-&gt;depth=8;
854 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
855 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
856 break;
857 /*
858 Convert MGK raster image to pixel packets.
859 */
860 if (SetImageExtent(image,0,0) == MagickFalse)
861 {
862 InheritException(exception,&amp;image-&gt;exception);
863 return(DestroyImageList(image));
864 }
865 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
866 if (pixels == (unsigned char *) NULL)
867 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
868 for (y=0; y &lt; (long) image-&gt;rows; y++)
869 {
870 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
871 if (count != (ssize_t) (3*image-&gt;columns))
872 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
873 p=pixels;
874 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
875 if (q == (PixelPacket *) NULL)
876 break;
877 for (x=0; x &lt; (long) image-&gt;columns; x++)
878 {
879 q-&gt;red=ScaleCharToQuantum(*p++);
880 q-&gt;green=ScaleCharToQuantum(*p++);
881 q-&gt;blue=ScaleCharToQuantum(*p++);
882 q++;
883 }
884 if (SyncAuthenticPixels(image,exception) == MagickFalse)
885 break;
886 if ((image-&gt;previous == (Image *) NULL) &&
887 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
888 break;
889 }
890 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
891 if (EOFBlob(image) != MagickFalse)
892 {
893 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
894 break;
895 }
896 /*
897 Proceed to next image.
898 */
899 if (image_info-&gt;number_scenes != 0)
900 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
901 break;
902 *buffer='\0';
903 (void) ReadBlobString(image,buffer);
904 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
905 if (count != 0)
906 {
907 /*
908 Allocate next image structure.
909 */
910 AcquireNextImage(image_info,image);
911 if (GetNextImageInList(image) == (Image *) NULL)
912 {
913 image=DestroyImageList(image);
914 return((Image *) NULL);
915 }
916 image=SyncNextImageInList(image);
917 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
918 if (status == MagickFalse)
919 break;
920 }
921 } while (count != 0);
922 (void) CloseBlob(image);
923 return(GetFirstImageInList(image));
924}
925
926/*
927%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
928% %
929% %
930% %
931% R e g i s t e r M G K I m a g e %
932% %
933% %
934% %
935%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
936%
937% RegisterMGKImage() adds attributes for the MGK image format to
938% the list of supported formats. The attributes include the image format
939% tag, a method to read and/or write the format, whether the format
940% supports the saving of more than one frame to the same file or blob,
941% whether the format supports native in-memory I/O, and a brief
942% description of the format.
943%
944% The format of the RegisterMGKImage method is:
945%
946% unsigned long RegisterMGKImage(void)
947%
948*/
949ModuleExport unsigned long RegisterMGKImage(void)
950{
951 MagickInfo
952 *entry;
953
954 entry=SetMagickInfo("MGK");
955 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
956 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
957 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
958 entry-&gt;description=ConstantString("MGK");
959 entry-&gt;module=ConstantString("MGK");
960 (void) RegisterMagickInfo(entry);
961 return(MagickImageCoderSignature);
962}
963
964/*
965%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
966% %
967% %
968% %
969% U n r e g i s t e r M G K I m a g e %
970% %
971% %
972% %
973%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
974%
975% UnregisterMGKImage() removes format registrations made by the
976% MGK module from the list of supported formats.
977%
978% The format of the UnregisterMGKImage method is:
979%
980% UnregisterMGKImage(void)
981%
982*/
983ModuleExport void UnregisterMGKImage(void)
984{
985 (void) UnregisterMagickInfo("MGK");
986}
987
988/*
989%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
990% %
991% %
992% %
993% W r i t e M G K I m a g e %
994% %
995% %
996% %
997%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
998%
999% WriteMGKImage() writes an image to a file in red, green, and blue
1000% MGK rasterfile format.
1001%
1002% The format of the WriteMGKImage method is:
1003%
1004% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1005%
1006% A description of each parameter follows.
1007%
1008% o image_info: the image info.
1009%
1010% o image: The image.
1011%
1012*/
1013static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1014{
1015 char
1016 buffer[MaxTextExtent];
1017
1018 long
1019 y;
1020
1021 MagickBooleanType
1022 status;
1023
1024 MagickOffsetType
1025 scene;
1026
1027 register const PixelPacket
1028 *p;
1029
1030 register long
1031 x;
1032
1033 register unsigned char
1034 *q;
1035
1036 unsigned char
1037 *pixels;
1038
1039 /*
1040 Open output image file.
1041 */
1042 assert(image_info != (const ImageInfo *) NULL);
1043 assert(image_info-&gt;signature == MagickSignature);
1044 assert(image != (Image *) NULL);
1045 assert(image-&gt;signature == MagickSignature);
1046 if (image-&gt;debug != MagickFalse)
1047 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1048 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1049 if (status == MagickFalse)
1050 return(status);
1051 scene=0;
1052 do
1053 {
1054 /*
1055 Allocate memory for pixels.
1056 */
1057 if (image-&gt;colorspace != RGBColorspace)
1058 (void) SetImageColorspace(image,RGBColorspace);
1059 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1060 3UL*sizeof(*pixels));
1061 if (pixels == (unsigned char *) NULL)
1062 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1063 /*
1064 Initialize raster file header.
1065 */
1066 (void) WriteBlobString(image,"id=mgk\n");
1067 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1068 image-&gt;columns,image-&gt;rows);
1069 (void) WriteBlobString(image,buffer);
1070 for (y=0; y &lt; (long) image-&gt;rows; y++)
1071 {
1072 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1073 if (p == (const PixelPacket *) NULL)
1074 break;
1075 q=pixels;
1076 for (x=0; x &lt; (long) image-&gt;columns; x++)
1077 {
1078 *q++=ScaleQuantumToChar(p-&gt;red);
1079 *q++=ScaleQuantumToChar(p-&gt;green);
1080 *q++=ScaleQuantumToChar(p-&gt;blue);
1081 p++;
1082 }
1083 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
1084 if ((image-&gt;previous == (Image *) NULL) &&
1085 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1086 break;
1087 }
1088 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1089 if (GetNextImageInList(image) == (Image *) NULL)
1090 break;
1091 image=SyncNextImageInList(image);
1092 status=SetImageProgress(image,SaveImagesTag,scene,
1093 GetImageListLength(image));
1094 if (status == MagickFalse)
1095 break;
1096 scene++;
1097 } while (image_info-&gt;adjoin != MagickFalse);
1098 (void) CloseBlob(image);
1099 return(MagickTrue);
1100}
1101</pre>
1102</div>
1103
1104<p>To invoke the custom coder from the command line, use these commands:</p>
1105
1106<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>
1107<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>
1108
1109</div>
1110
1111<h2><a name="filters"></a>Custom Image Filters</h2>
1112<div class="doc-section">
1113
1114<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>
1115
1116<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>
1117
1118<div class="viewport">
1119<pre class="code">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1120#include &lt;stdio.h&gt;
1121#include &lt;stdlib.h&gt;
1122#include &lt;string.h&gt;
1123#include &lt;time.h&gt;
1124#include &lt;assert.h&gt;
1125#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1126#include "magick/MagickCore.h"
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1127
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1128/*
1129%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1130% %
1131% %
1132% %
1133% a n a l y z e I m a g e %
1134% %
1135% %
1136% %
1137%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1138%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1139% analyzeImage() computes the brightness and saturation mean, standard
1140% deviation, kurtosis and skewness and stores these values as attributes
1141% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1142%
1143% The format of the analyzeImage method is:
1144%
1145% unsigned long analyzeImage(Image *images,const int argc,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1146% char **argv,ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1147%
1148% A description of each parameter follows:
1149%
1150% o image: the address of a structure of type Image.
1151%
1152% o argc: Specifies a pointer to an integer describing the number of
1153% elements in the argument vector.
1154%
1155% o argv: Specifies a pointer to a text array containing the command line
1156% arguments.
1157%
1158% o exception: return any errors or warnings in this structure.
1159%
1160*/
1161ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1162 const char **argv,ExceptionInfo *exception)
1163{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1164 char
1165 text[MaxTextExtent];
1166
1167 double
1168 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1169 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1170 brightness_mean,
1171 brightness_standard_deviation,
1172 brightness_kurtosis,
1173 brightness_skewness,
1174 brightness_sum_x,
1175 brightness_sum_x2,
1176 brightness_sum_x3,
1177 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1178 hue,
1179 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1180 saturation_mean,
1181 saturation_standard_deviation,
1182 saturation_kurtosis,
1183 saturation_skewness,
1184 saturation_sum_x,
1185 saturation_sum_x2,
1186 saturation_sum_x3,
1187 saturation_sum_x4;
1188
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1189 Image
1190 *image;
1191
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1192 assert(images != (Image **) NULL);
1193 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1194 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1195 (void) argc;
1196 (void) argv;
1197 image=(*images);
1198 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1199 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1200 CacheView
1201 *image_view;
1202
1203 long
1204 y;
1205
1206 MagickBooleanType
1207 status;
1208
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1209 brightness_sum_x=0.0;
1210 brightness_sum_x2=0.0;
1211 brightness_sum_x3=0.0;
1212 brightness_sum_x4=0.0;
1213 brightness_mean=0.0;
1214 brightness_standard_deviation=0.0;
1215 brightness_kurtosis=0.0;
1216 brightness_skewness=0.0;
1217 saturation_sum_x=0.0;
1218 saturation_sum_x2=0.0;
1219 saturation_sum_x3=0.0;
1220 saturation_sum_x4=0.0;
1221 saturation_mean=0.0;
1222 saturation_standard_deviation=0.0;
1223 saturation_kurtosis=0.0;
1224 saturation_skewness=0.0;
1225 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1226 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1227 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1228#if defined(MAGICKCORE_OPENMP_SUPPORT)
1229 #pragma omp parallel for schedule(dynamic,4) shared(status)
1230#endif
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1231 for (y=0; y &lt; (long) image-&gt;rows; y++)
1232 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1233 register const PixelPacket
1234 *p;
1235
1236 register long
1237 x;
1238
1239 if (status == MagickFalse)
1240 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1241 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1242 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1243 {
1244 status=MagickFalse;
1245 continue;
1246 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1247 for (x=0; x &lt; (long) image-&gt;columns; x++)
1248 {
1249 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1250 brightness*=QuantumRange;
1251 brightness_sum_x+=brightness;
1252 brightness_sum_x2+=brightness*brightness;
1253 brightness_sum_x3+=brightness*brightness*brightness;
1254 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1255 saturation*=QuantumRange;
1256 saturation_sum_x+=saturation;
1257 saturation_sum_x2+=saturation*saturation;
1258 saturation_sum_x3+=saturation*saturation*saturation;
1259 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1260 area++;
1261 p++;
1262 }
1263 }
1264 image_view=DestroyCacheView(image_view);
1265 if (area &lt;= 0.0)
1266 break;
1267 brightness_mean=brightness_sum_x/area;
1268 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1269 (void) SetImageProperty(image,"filter:brightness:mean",text);
1270 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1271 area*brightness_sum_x/area));
1272 (void) FormatMagickString(text,MaxTextExtent,"%g",
1273 brightness_standard_deviation);
1274 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1275 if (brightness_standard_deviation != 0)
1276 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1277 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1278 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1279 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1280 brightness_standard_deviation*brightness_standard_deviation*
1281 brightness_standard_deviation)-3.0;
1282 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1283 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1284 if (brightness_standard_deviation != 0)
1285 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1286 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1287 brightness_mean)/(brightness_standard_deviation*
1288 brightness_standard_deviation*brightness_standard_deviation);
1289 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1290 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1291 saturation_mean=saturation_sum_x/area;
1292 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1293 (void) SetImageProperty(image,"filter:saturation:mean",text);
1294 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1295 area*saturation_sum_x/area));
1296 (void) FormatMagickString(text,MaxTextExtent,"%g",
1297 saturation_standard_deviation);
1298 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1299 if (saturation_standard_deviation != 0)
1300 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1301 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1302 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1303 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1304 saturation_standard_deviation*saturation_standard_deviation*
1305 saturation_standard_deviation)-3.0;
1306 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1307 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1308 if (saturation_standard_deviation != 0)
1309 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1310 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1311 saturation_mean)/(saturation_standard_deviation*
1312 saturation_standard_deviation*saturation_standard_deviation);
1313 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1314 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1315 }
1316 return(MagickImageFilterSignature);
1317}
1318</pre>
1319</div>
1320
1321<p>To invoke the custom filter from the command line, use this command:</p>
1322
1323<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/>
1324 Format: LOGO (ImageMagick Logo) <br/>
1325 Class: PseudoClass <br/>
1326 Geometry: 640x480 <br/>
1327 ... <br/>
1328 filter:brightness:kurtosis: 8.98864 <br/>
1329 filter:brightness:mean: 238.096 <br/>
1330 filter:brightness:skewness: -3.04519 <br/>
1331 filter:brightness:standard-deviation: 46.3286 <br/>
1332 filter:saturation:kurtosis: 5.9137 <br/>
1333 filter:saturation:mean: 23.4635 <br/>
1334 filter:saturation:skewness: 2.71874 <br/>
1335 filter:saturation:standard-deviation: 64.7734</span></p>
1336
1337<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>
1338
1339</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1340
1341</div>
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