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156<div class="main">
157
158
159
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]160<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]161
162<div class="doc-section">
163<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>
164</div>
165
166<h2><a name="overview"></a>Architecture Overview</h2>
167<div class="doc-section">
168
169<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>
170
171<ul>
172 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
173 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
174 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
175 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
176 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
177 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
178</ul>
179
180<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>
181
182<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
183
184<ul>
185 <li>one pixel a time (e.g. pixel at location 10,3)</li>
186 <li>a single scanline (e.g. all pixels from row 4)</li>
187 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
188 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
189 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
190 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
191 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
192 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
193 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
194 <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>
195 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]196 <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]197</ul>
198
199<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>
200
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]201<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]202
203<p>In addition to pixels, images have a plethora of <a href="#properties">image properties and profiles</a>. Properties include the well known items 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>
204
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]205<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]206
207</div>
208
209<h2><a name="cache"></a>The Pixel Cache</h2>
210<div class="doc-section">
211
212<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>
213
214<h3>Create the Pixel Cache</h3>
215<div class="doc-section">
216
217<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>
218
219<h4>Create an image canvas initialized to the background color:</h4>
220<p class="code">
221 image=AllocateImage(image_info);
222 if (SetImageExtent(image,640,480) == MagickFalse)
223 { /* an exception was thrown */ }
224 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
225 SetImageBackgroundColor(image);
226</p>
227
228<h4>Create an image from a JPEG image on disk:</h4>
229<p class="code"> (void) strcpy(image_info-&gt;filename,"image.jpg"):
230 image=ReadImage(image_info,exception);
231 if (image == (Image *) NULL)
232 { /* an exception was thrown */ }
233</p>
234<h4>Create an image from a memory based image:</h4>
235<p class="code">
236 image=BlobToImage(blob_info,blob,extent,exception);
237 if (image == (Image *) NULL)
238 { /* an exception was thrown */ }
239</p>
240
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]241<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]242
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]243<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]244
cristy65f305a2010-02-13 13:52:40 +0000[diff] [blame]245<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.5.9-4 2010-02-15 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]246<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]247</div>
248
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]249<h3><a name="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]250<div class="doc-section">
251
252<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>
253<ul>
254 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify</li>
255 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
256 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
257 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
258</ul>
259
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]260<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]261
262<div class="viewport">
263<pre class="code">
264 long
265 x,
266 y;
267
268 const PixelPacket
269 *p;
270
271 PixelPacket
272 *q;
273
274 destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
275 if (destination == (Image *) NULL)
276 { /* an exception was thrown */ }
277 for (y=0; y &lt; (long) source-&gt;rows; y++)
278 {
279 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
280 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
281 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
282 break;
283 for (x=0; x &lt; (long) source-&gt;columns; x++)
284 {
285 q-&gt;red=90*p-&gt;red/100;
286 q-&gt;green=90*p-&gt;green/100;
287 q-&gt;blue=90*p-&gt;blue/100;
288 q-&gt;opacity=90*p-&gt;opacity/100;
289 p++;
290 q++;
291 }
292 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
293 break;
294 }
295 if (y &lt; (long) source-&gt;rows)
296 { /* an exception was thrown */ }
297</pre>
298</div>
299
300<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>
301
302<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>
303
304<pre class="code">
305 const IndexPacket
306 *indexes;
307
308 for (y=0; y &lt; (long) source-&gt;rows; y++)
309 {
310 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
311 if (p == (const PixelPacket *) NULL)
312 break;
313 indexes=GetVirtualIndexes(source);
314 for (x=0; x &lt; (long) source-&gt;columns; x++)
315 (void) printf("%d\n",indexes[x];
316 }
317 if (y &lt; (long) source-&gt;rows)
318 /* an exception was thrown */
319</pre>
320
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]321<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]322
323<pre class="code">
324 p=GetVirtualPixels(source,-3,3,source-&gt;columns+7,7,exception);
325</pre>
326
327<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
328</div>
329
330<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
331<div class="doc-section">
332
333 <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>
334
335<pre class="text">
336 background: the area surrounding the image is the background color
337 black: the area surrounding the image is black
338 checker-tile: alternate squares with image and background color
339 dither: non-random 32x32 dithered pattern
340 edge: extend the edge pixel toward infinity
341 gray: the area surrounding the image is gray
342 horizontal-tile: horizontally tile the image, background color above/below
343 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
344 mirror: mirror tile the image
345 random: choose a random pixel from the image
346 tile: tile the image (default)
347 transparent: the area surrounding the image is transparent blackness
348 vertical-tile: vertically tile the image, sides are background color
349 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
350 white: the area surrounding the image is white
351</pre>
352
353<p>There is a plethora of image processing algorithms that require a neighborhood of pixels about a pixel of interest. There is typically 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>
354</div>
355
356<h3>Cache Storage and Resource Requirements</h3>
357<div class="doc-section">
358
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]359<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]360
361<dl class="doc">
362 <dt class="doc">files</dt>
363 <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>
364 <dt class="doc">area</dt>
365 <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>
366 <dt class="doc">memory</dt>
367 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
368 <dt class="doc">map</dt>
369 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
370 <dt class="doc">disk</dt>
371 <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>
372</dl>
373
374<p>To determine the current setting of these limits, use this command:</p>
375
cristyc1c61662009-09-30 14:04:37 +0000[diff] [blame]376<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
377------------------------------------------------------------------------
378 768 11.551GiB 8.6631GiB 23.102GiB 16EiB 8 unlimited</pre></span></p>
379<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 mebibytes, a memory limit of 128 mebibytes and a map limit of 256 mebibytes and a disk limit of 1 gibibytes. 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]380
381<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>
382</div>
383
384<h3>Cache Views</h3>
385<div class="doc-section">
386
387<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>
388
389<pre class="code">
390 CacheView
391 *view_1,
392 *view_2;
393
394 view_1=OpenCacheView(source);
395 view_2=OpenCacheView(source);
396 for (y=0; y &lt; (long) source-&gt;rows; y++)
397 {
398 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
399 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,exception);
400 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
401 break;
402 for (x=0; x &lt; (long) source-&gt;columns; x++)
403 {
404 /* do something with u &amp; v here */
405 }
406 }
407 view_1=CloseCacheView(view_1);
408 view_2=CloseCacheView(view_2);
409 if (y &lt; (long) source-&gt;rows)
410 { /* an exception was thrown */ }
411</pre>
412</div>
413
414<h3>Magick Persistent Cache Format</h3>
415<div class="doc-section">
416
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]417<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]418</div>
419
420<h3>Best Practices</h3>
421<div class="doc-section">
422
423<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>
424
425<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>
426
427<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>
428
429<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>
430
431<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>
432
433<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>
434
435<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>
436
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]437<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]438
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]439<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]440
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]441<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]442
443<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>
444
445<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>
446<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>
447</div>
448
449</div>
450
451<h2><a name="stream"></a>Streaming Pixels</h2>
452<div class="doc-section">
453
454<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>
455
456<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>
457
458<pre class="code">
459static size_t StreamHandler(const Image *image,const void *pixels,
460 const size_t columns)
461{
462 /* process pixels here */
463 return(columns);
464}
465
466...
467/* invoke the pixel stream here */
468image=ReadStream(image_info,&amp;StreamHandler,exception);
469</pre>
470
471<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>
472
473</div>
474
475<h2><a name="properties"></a>Image Properties and Profiles</h2>
476<div class="doc-section">
477
478<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>
479
480<pre class="code">
481 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
482</pre>
483
484<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>
485
486<pre class="code">
487 const char
488 *comment;
489
490 (void) SetImageProperty(image,"comment","This space for rent");
491 comment=GetImageProperty(image,"comment");
492 if (comment == (const char *) NULL)
493 (void) printf("Image comment: %s\n",comment);
494</pre>
495
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]496<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>
497
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]498<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>
499
500<pre class="code">
501 StringInfo
502 *profile;
503
504 profile=AcquireStringInfo(length);
505 SetStringInfoDatum(profile,my_exif_profile);
506 (void) SetImageProfile(image,"EXIF",profile);
507 DestroyStringInfo(profile);
508 profile=GetImageProfile(image,"EXIF");
509 if (profile != (StringInfo *) NULL)
510 (void) PrintStringInfo(stdout,"EXIF",profile);
511</pre>
512
513</div>
514
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]515<h2><a name="tera-pixel"></a>Large Image Support</h2>
516<div class="doc-section">
517<p>ImageMagick can read, process, or write mega-, giga-, or tera-pixel image sizes. For example, here we resize an image to a quarter million pixels square:</p>
518
519<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: -resize 250000x250000 logo.miff</span></p>
520<p>For large images, ImageMagick will more than 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>
521
522<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp logo: -resize 250000x250000 logo.miff</span></p>
523<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>
524
525<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit memory 16mb logo: -resize 250000x250000 logo.miff</span></p>
526<p>Here we force all image pixels to disk:</p>
527
528<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit area 0 logo: -resize 250000x250000 logo.miff</span></p>
529<p>Caching pixels to disk is about 1000 times slower than memory. Expect long run times when processing large images with ImageMagick. You can monitor progress with this command:</p>
530
531<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -monitor -define registry:temporary-path=/data/tmp -limit area 0 logo: -resize 250000x250000 logo.miff</span></p></div>
532
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]533<h2><a name="threads"></a>Threads of Execution</h2>
534<div class="doc-section">
535
536<p>Many of ImageMagick's internal algorithms are threaded to take advantage of speed-ups offered by the dual and quad-core processor technologies. 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>
537
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]538<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]539
540<div class="viewport">
541<pre class="code">
542{
543 CacheView
544 *image_view;
545
546 long
547 y;
548
549 MagickBooleanType
550 status;
551
552 status=MagickTrue;
553 image_view=AcquireCacheView(image);
554 #pragma omp parallel for schedule(dynamic,4) shared(status)
555 for (y=0; y &lt; (long) image-&gt;rows; y++)
556 {
557 register IndexPacket
558 *indexes;
559
560 register long
561 x;
562
563 register PixelPacket
564 *q;
565
566 if (status == MagickFalse)
567 continue;
568 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
569 if (q == (PixelPacket *) NULL)
570 {
571 status=MagickFalse;
572 continue;
573 }
574 indexes=GetCacheViewAuthenticIndexQueue(image_view);
575 for (x=0; x &lt; (long) image-&gt;columns; x++)
576 {
577 q-&gt;red= ...
578 q-&gt;green= ...
579 q-&gt;blue= ...
580 q-&gt;opacity= ...
581 if (indexes != (IndexPacket *) NULL)
582 indexes[x]= ...
583 q++;
584 }
585 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
586 status=MagickFalse;
587 }
588 image_view=DestroyCacheView(image_view);
589 if (status == MagickFalse)
590 perror("something went wrong");
591}
592</pre>
593</div>
594
595<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>
596
597</div>
598
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]599<h2><a name="distributed"></a>Heterogeneous Distributed Processing</h2>
600<div class="doc-section">
601<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>
602
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]603<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]604
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]605<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
606<p>If so, run this command to realize a significant speed-up for image convolution:</p>
607
608<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' convolve.png</span></p>
609<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
610
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]611<p>Here is an example OpenCL kernel that convolves an image:</p>
612
613<div class="viewport">
614<pre class="code">
615static inline long ClampToCanvas(const long offset,const ulong range)
616{
617 if (offset &lt; 0L)
618 return(0L);
619 if (offset >= range)
620 return((long) (range-1L));
621 return(offset);
622}
623
624static inline CLQuantum ClampToQuantum(const double value)
625{
626 if (value &lt; 0.0)
627 return((CLQuantum) 0);
628 if (value >= (double) QuantumRange)
629 return((CLQuantum) QuantumRange);
630 return((CLQuantum) (value+0.5));
631}
632
633__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
634 const ulong width,const ulong height,__global CLPixelType *destination)
635{
636 const ulong columns = get_global_size(0);
637 const ulong rows = get_global_size(1);
638
639 const long x = get_global_id(0);
640 const long y = get_global_id(1);
641
642 const double scale = (1.0/QuantumRange);
643 const long mid_width = (width-1)/2;
644 const long mid_height = (height-1)/2;
645 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
646 double gamma = 0.0;
647 register ulong i = 0;
648
649 for (long v=(-mid_height); v &lt;= mid_height; v++)
650 {
651 for (long u=(-mid_width); u &lt;= mid_width; u++)
652 {
653 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,columns);
654 const double alpha=scale*(QuantumRange-source[index].w);
655 sum.x+=alpha*filter[i]*source[index].x;
656 sum.y+=alpha*filter[i]*source[index].y;
657 sum.z+=alpha*filter[i]*source[index].z;
658 sum.w+=filter[i]*source[index].w;
659 gamma+=alpha*filter[i];
660 i++;
661 }
662 }
663
664 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
665 const ulong index=y*columns+x;
666 destination[index].x=ClampToQuantum(gamma*sum.x);
667 destination[index].y=ClampToQuantum(gamma*sum.y);
668 destination[index].z=ClampToQuantum(gamma*sum.z);
669 destination[index].w=ClampToQuantum(sum.w);
670};
671</pre>
672</div>
673
674<p>See <a href="http://trac.imagemagick.org/browser/ImageMagick/trunk/filters/convolve.c">filters/convolve.c</a> for a complete implementation of image convolution with an OpenCL kernel.</p>
675
676</div>
677
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]678<h2><a name="coders"></a>Custom Image Coders</h2>
679<div class="doc-section">
680
681<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>
682
683<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>
684
685<div class="viewport">
686<pre class="code">
687/*
688 Include declarations.
689*/
690#include "magick/studio.h"
691#include "magick/blob.h"
692#include "magick/blob-private.h"
693#include "magick/colorspace.h"
694#include "magick/exception.h"
695#include "magick/exception-private.h"
696#include "magick/image.h"
697#include "magick/image-private.h"
698#include "magick/list.h"
699#include "magick/magick.h"
700#include "magick/memory_.h"
701#include "magick/monitor.h"
702#include "magick/monitor-private.h"
703#include "magick/quantum-private.h"
704#include "magick/static.h"
705#include "magick/string_.h"
706#include "magick/module.h"
707
708/*
709 Forward declarations.
710*/
711static MagickBooleanType
712 WriteMGKImage(const ImageInfo *,Image *);
713
714/*
715%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
716% %
717% %
718% %
719% I s M G K %
720% %
721% %
722% %
723%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
724%
725% IsMGK() returns MagickTrue if the image format type, identified by the
726% magick string, is MGK.
727%
728% The format of the IsMGK method is:
729%
730% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
731%
732% A description of each parameter follows:
733%
734% o magick: This string is generally the first few bytes of an image file
735% or blob.
736%
737% o length: Specifies the length of the magick string.
738%
739*/
740static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
741{
742 if (length &lt; 7)
743 return(MagickFalse);
744 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
745 return(MagickTrue);
746 return(MagickFalse);
747}
748
749/*
750%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
751% %
752% %
753% %
754% R e a d M G K I m a g e %
755% %
756% %
757% %
758%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
759%
760% ReadMGKImage() reads a MGK image file and returns it. It allocates
761% the memory necessary for the new Image structure and returns a pointer to
762% the new image.
763%
764% The format of the ReadMGKImage method is:
765%
766% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
767%
768% A description of each parameter follows:
769%
770% o image_info: the image info.
771%
772% o exception: return any errors or warnings in this structure.
773%
774*/
775static Image *ReadMGKImage(const ImageInfo *image_info,
776 ExceptionInfo *exception)
777{
778 char
779 buffer[MaxTextExtent];
780
781 Image
782 *image;
783
784 long
785 y;
786
787 MagickBooleanType
788 status;
789
790 register long
791 x;
792
793 register PixelPacket
794 *q;
795
796 register unsigned char
797 *p;
798
799 ssize_t
800 count;
801
802 unsigned char
803 *pixels;
804
805 unsigned long
806 columns,
807 rows;
808
809 /*
810 Open image file.
811 */
812 assert(image_info != (const ImageInfo *) NULL);
813 assert(image_info-&gt;signature == MagickSignature);
814 if (image_info-&gt;debug != MagickFalse)
815 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
816 assert(exception != (ExceptionInfo *) NULL);
817 assert(exception-&gt;signature == MagickSignature);
818 image=AcquireImage(image_info);
819 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
820 if (status == MagickFalse)
821 {
822 image=DestroyImageList(image);
823 return((Image *) NULL);
824 }
825 /*
826 Read MGK image.
827 */
828 (void) ReadBlobString(image,buffer); /* read magic number */
829 if (IsMGK(buffer,7) == MagickFalse)
830 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
831 (void) ReadBlobString(image,buffer);
832 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
833 if (count &lt;= 0)
834 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
835 do
836 {
837 /*
838 Initialize image structure.
839 */
840 image-&gt;columns=columns;
841 image-&gt;rows=rows;
842 image-&gt;depth=8;
843 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
844 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
845 break;
846 /*
847 Convert MGK raster image to pixel packets.
848 */
849 if (SetImageExtent(image,0,0) == MagickFalse)
850 {
851 InheritException(exception,&amp;image-&gt;exception);
852 return(DestroyImageList(image));
853 }
854 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
855 if (pixels == (unsigned char *) NULL)
856 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
857 for (y=0; y &lt; (long) image-&gt;rows; y++)
858 {
859 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
860 if (count != (ssize_t) (3*image-&gt;columns))
861 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
862 p=pixels;
863 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
864 if (q == (PixelPacket *) NULL)
865 break;
866 for (x=0; x &lt; (long) image-&gt;columns; x++)
867 {
868 q-&gt;red=ScaleCharToQuantum(*p++);
869 q-&gt;green=ScaleCharToQuantum(*p++);
870 q-&gt;blue=ScaleCharToQuantum(*p++);
871 q++;
872 }
873 if (SyncAuthenticPixels(image,exception) == MagickFalse)
874 break;
875 if ((image-&gt;previous == (Image *) NULL) &&
876 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
877 break;
878 }
879 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
880 if (EOFBlob(image) != MagickFalse)
881 {
882 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
883 break;
884 }
885 /*
886 Proceed to next image.
887 */
888 if (image_info-&gt;number_scenes != 0)
889 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
890 break;
891 *buffer='\0';
892 (void) ReadBlobString(image,buffer);
893 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
894 if (count != 0)
895 {
896 /*
897 Allocate next image structure.
898 */
899 AcquireNextImage(image_info,image);
900 if (GetNextImageInList(image) == (Image *) NULL)
901 {
902 image=DestroyImageList(image);
903 return((Image *) NULL);
904 }
905 image=SyncNextImageInList(image);
906 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
907 if (status == MagickFalse)
908 break;
909 }
910 } while (count != 0);
911 (void) CloseBlob(image);
912 return(GetFirstImageInList(image));
913}
914
915/*
916%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
917% %
918% %
919% %
920% R e g i s t e r M G K I m a g e %
921% %
922% %
923% %
924%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
925%
926% RegisterMGKImage() adds attributes for the MGK image format to
927% the list of supported formats. The attributes include the image format
928% tag, a method to read and/or write the format, whether the format
929% supports the saving of more than one frame to the same file or blob,
930% whether the format supports native in-memory I/O, and a brief
931% description of the format.
932%
933% The format of the RegisterMGKImage method is:
934%
935% unsigned long RegisterMGKImage(void)
936%
937*/
938ModuleExport unsigned long RegisterMGKImage(void)
939{
940 MagickInfo
941 *entry;
942
943 entry=SetMagickInfo("MGK");
944 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
945 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
946 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
947 entry-&gt;description=ConstantString("MGK");
948 entry-&gt;module=ConstantString("MGK");
949 (void) RegisterMagickInfo(entry);
950 return(MagickImageCoderSignature);
951}
952
953/*
954%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
955% %
956% %
957% %
958% U n r e g i s t e r M G K I m a g e %
959% %
960% %
961% %
962%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
963%
964% UnregisterMGKImage() removes format registrations made by the
965% MGK module from the list of supported formats.
966%
967% The format of the UnregisterMGKImage method is:
968%
969% UnregisterMGKImage(void)
970%
971*/
972ModuleExport void UnregisterMGKImage(void)
973{
974 (void) UnregisterMagickInfo("MGK");
975}
976
977/*
978%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
979% %
980% %
981% %
982% W r i t e M G K I m a g e %
983% %
984% %
985% %
986%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
987%
988% WriteMGKImage() writes an image to a file in red, green, and blue
989% MGK rasterfile format.
990%
991% The format of the WriteMGKImage method is:
992%
993% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
994%
995% A description of each parameter follows.
996%
997% o image_info: the image info.
998%
999% o image: The image.
1000%
1001*/
1002static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1003{
1004 char
1005 buffer[MaxTextExtent];
1006
1007 long
1008 y;
1009
1010 MagickBooleanType
1011 status;
1012
1013 MagickOffsetType
1014 scene;
1015
1016 register const PixelPacket
1017 *p;
1018
1019 register long
1020 x;
1021
1022 register unsigned char
1023 *q;
1024
1025 unsigned char
1026 *pixels;
1027
1028 /*
1029 Open output image file.
1030 */
1031 assert(image_info != (const ImageInfo *) NULL);
1032 assert(image_info-&gt;signature == MagickSignature);
1033 assert(image != (Image *) NULL);
1034 assert(image-&gt;signature == MagickSignature);
1035 if (image-&gt;debug != MagickFalse)
1036 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1037 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1038 if (status == MagickFalse)
1039 return(status);
1040 scene=0;
1041 do
1042 {
1043 /*
1044 Allocate memory for pixels.
1045 */
1046 if (image-&gt;colorspace != RGBColorspace)
1047 (void) SetImageColorspace(image,RGBColorspace);
1048 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1049 3UL*sizeof(*pixels));
1050 if (pixels == (unsigned char *) NULL)
1051 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1052 /*
1053 Initialize raster file header.
1054 */
1055 (void) WriteBlobString(image,"id=mgk\n");
1056 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1057 image-&gt;columns,image-&gt;rows);
1058 (void) WriteBlobString(image,buffer);
1059 for (y=0; y &lt; (long) image-&gt;rows; y++)
1060 {
1061 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1062 if (p == (const PixelPacket *) NULL)
1063 break;
1064 q=pixels;
1065 for (x=0; x &lt; (long) image-&gt;columns; x++)
1066 {
1067 *q++=ScaleQuantumToChar(p-&gt;red);
1068 *q++=ScaleQuantumToChar(p-&gt;green);
1069 *q++=ScaleQuantumToChar(p-&gt;blue);
1070 p++;
1071 }
1072 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
1073 if ((image-&gt;previous == (Image *) NULL) &&
1074 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1075 break;
1076 }
1077 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1078 if (GetNextImageInList(image) == (Image *) NULL)
1079 break;
1080 image=SyncNextImageInList(image);
1081 status=SetImageProgress(image,SaveImagesTag,scene,
1082 GetImageListLength(image));
1083 if (status == MagickFalse)
1084 break;
1085 scene++;
1086 } while (image_info-&gt;adjoin != MagickFalse);
1087 (void) CloseBlob(image);
1088 return(MagickTrue);
1089}
1090</pre>
1091</div>
1092
1093<p>To invoke the custom coder from the command line, use these commands:</p>
1094
1095<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>
1096<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>
1097
1098</div>
1099
1100<h2><a name="filters"></a>Custom Image Filters</h2>
1101<div class="doc-section">
1102
1103<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>
1104
1105<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>
1106
1107<div class="viewport">
1108<pre class="code">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1109#include &lt;stdio.h&gt;
1110#include &lt;stdlib.h&gt;
1111#include &lt;string.h&gt;
1112#include &lt;time.h&gt;
1113#include &lt;assert.h&gt;
1114#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1115#include "magick/MagickCore.h"
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1116
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1117/*
1118%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1119% %
1120% %
1121% %
1122% a n a l y z e I m a g e %
1123% %
1124% %
1125% %
1126%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1127%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1128% analyzeImage() computes the brightness and saturation mean, standard
1129% deviation, kurtosis and skewness and stores these values as attributes
1130% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1131%
1132% The format of the analyzeImage method is:
1133%
1134% unsigned long analyzeImage(Image *images,const int argc,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1135% char **argv,ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1136%
1137% A description of each parameter follows:
1138%
1139% o image: the address of a structure of type Image.
1140%
1141% o argc: Specifies a pointer to an integer describing the number of
1142% elements in the argument vector.
1143%
1144% o argv: Specifies a pointer to a text array containing the command line
1145% arguments.
1146%
1147% o exception: return any errors or warnings in this structure.
1148%
1149*/
1150ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1151 const char **argv,ExceptionInfo *exception)
1152{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1153 char
1154 text[MaxTextExtent];
1155
1156 double
1157 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1158 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1159 brightness_mean,
1160 brightness_standard_deviation,
1161 brightness_kurtosis,
1162 brightness_skewness,
1163 brightness_sum_x,
1164 brightness_sum_x2,
1165 brightness_sum_x3,
1166 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1167 hue,
1168 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1169 saturation_mean,
1170 saturation_standard_deviation,
1171 saturation_kurtosis,
1172 saturation_skewness,
1173 saturation_sum_x,
1174 saturation_sum_x2,
1175 saturation_sum_x3,
1176 saturation_sum_x4;
1177
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1178 Image
1179 *image;
1180
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1181 assert(images != (Image **) NULL);
1182 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1183 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1184 (void) argc;
1185 (void) argv;
1186 image=(*images);
1187 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1188 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1189 CacheView
1190 *image_view;
1191
1192 long
1193 y;
1194
1195 MagickBooleanType
1196 status;
1197
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1198 brightness_sum_x=0.0;
1199 brightness_sum_x2=0.0;
1200 brightness_sum_x3=0.0;
1201 brightness_sum_x4=0.0;
1202 brightness_mean=0.0;
1203 brightness_standard_deviation=0.0;
1204 brightness_kurtosis=0.0;
1205 brightness_skewness=0.0;
1206 saturation_sum_x=0.0;
1207 saturation_sum_x2=0.0;
1208 saturation_sum_x3=0.0;
1209 saturation_sum_x4=0.0;
1210 saturation_mean=0.0;
1211 saturation_standard_deviation=0.0;
1212 saturation_kurtosis=0.0;
1213 saturation_skewness=0.0;
1214 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1215 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1216 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1217#if defined(MAGICKCORE_OPENMP_SUPPORT)
1218 #pragma omp parallel for schedule(dynamic,4) shared(status)
1219#endif
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1220 for (y=0; y &lt; (long) image-&gt;rows; y++)
1221 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1222 register const PixelPacket
1223 *p;
1224
1225 register long
1226 x;
1227
1228 if (status == MagickFalse)
1229 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1230 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1231 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1232 {
1233 status=MagickFalse;
1234 continue;
1235 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1236 for (x=0; x &lt; (long) image-&gt;columns; x++)
1237 {
1238 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1239 brightness*=QuantumRange;
1240 brightness_sum_x+=brightness;
1241 brightness_sum_x2+=brightness*brightness;
1242 brightness_sum_x3+=brightness*brightness*brightness;
1243 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1244 saturation*=QuantumRange;
1245 saturation_sum_x+=saturation;
1246 saturation_sum_x2+=saturation*saturation;
1247 saturation_sum_x3+=saturation*saturation*saturation;
1248 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1249 area++;
1250 p++;
1251 }
1252 }
1253 image_view=DestroyCacheView(image_view);
1254 if (area &lt;= 0.0)
1255 break;
1256 brightness_mean=brightness_sum_x/area;
1257 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1258 (void) SetImageProperty(image,"filter:brightness:mean",text);
1259 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1260 area*brightness_sum_x/area));
1261 (void) FormatMagickString(text,MaxTextExtent,"%g",
1262 brightness_standard_deviation);
1263 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1264 if (brightness_standard_deviation != 0)
1265 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1266 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1267 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1268 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1269 brightness_standard_deviation*brightness_standard_deviation*
1270 brightness_standard_deviation)-3.0;
1271 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1272 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1273 if (brightness_standard_deviation != 0)
1274 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1275 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1276 brightness_mean)/(brightness_standard_deviation*
1277 brightness_standard_deviation*brightness_standard_deviation);
1278 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1279 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1280 saturation_mean=saturation_sum_x/area;
1281 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1282 (void) SetImageProperty(image,"filter:saturation:mean",text);
1283 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1284 area*saturation_sum_x/area));
1285 (void) FormatMagickString(text,MaxTextExtent,"%g",
1286 saturation_standard_deviation);
1287 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1288 if (saturation_standard_deviation != 0)
1289 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1290 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1291 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1292 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1293 saturation_standard_deviation*saturation_standard_deviation*
1294 saturation_standard_deviation)-3.0;
1295 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1296 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1297 if (saturation_standard_deviation != 0)
1298 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1299 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1300 saturation_mean)/(saturation_standard_deviation*
1301 saturation_standard_deviation*saturation_standard_deviation);
1302 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1303 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1304 }
1305 return(MagickImageFilterSignature);
1306}
1307</pre>
1308</div>
1309
1310<p>To invoke the custom filter from the command line, use this command:</p>
1311
1312<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/>
1313 Format: LOGO (ImageMagick Logo) <br/>
1314 Class: PseudoClass <br/>
1315 Geometry: 640x480 <br/>
1316 ... <br/>
1317 filter:brightness:kurtosis: 8.98864 <br/>
1318 filter:brightness:mean: 238.096 <br/>
1319 filter:brightness:skewness: -3.04519 <br/>
1320 filter:brightness:standard-deviation: 46.3286 <br/>
1321 filter:saturation:kurtosis: 5.9137 <br/>
1322 filter:saturation:mean: 23.4635 <br/>
1323 filter:saturation:skewness: 2.71874 <br/>
1324 filter:saturation:standard-deviation: 64.7734</span></p>
1325
1326<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>
1327
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cristyf3bb4782009-09-08 13:10:04 +0000[diff] [blame]1329
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