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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="#threads">Threads of Execution</a> &bull; <a href="#coders">Custom Image Coders</a> &bull; <a href="#filters">Custom Image Filters</a>]</p>
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>
196</ul>
197
198<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>
199
200<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 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>
201
202<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>
203
204<p>ImageMagick consists of more than 375,000 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>
205
206</div>
207
208<h2><a name="cache"></a>The Pixel Cache</h2>
209<div class="doc-section">
210
211<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>
212
213<h3>Create the Pixel Cache</h3>
214<div class="doc-section">
215
216<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>
217
218<h4>Create an image canvas initialized to the background color:</h4>
219<p class="code">
220  image=AllocateImage(image_info);
221  if (SetImageExtent(image,640,480) == MagickFalse)
222    { /* an exception was thrown */ }
223  (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
224  SetImageBackgroundColor(image);
225</p>
226
227<h4>Create an image from a JPEG image on disk:</h4>
228<p class="code">  (void) strcpy(image_info-&gt;filename,"image.jpg"):
229  image=ReadImage(image_info,exception);
230  if (image == (Image *) NULL)
231    { /* an exception was thrown */ }
232</p>
233<h4>Create an image from a memory based image:</h4>
234<p class="code">
235  image=BlobToImage(blob_info,blob,extent,exception);
236  if (image == (Image *) NULL)
237    { /* an exception was thrown */ }
238</p>
239
240<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>
241
242<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 using the <a href="../www/command-line-options.html#version">&#x2011;version</a> option, as with this command: </p>
243
244<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.5.7-9 2009-11-01 Q16 http://www.imagemagick.org</span></p>
245<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).</p>
246</div>
247
248<h3>Access the Pixel Cache</h3>
249<div class="doc-section">
250
251<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>
252<ul>
253  <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify</li>
254  <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
255  <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
256  <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
257</ul>
258
259<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>
260
261<div class="viewport">
262<pre class="code">
263  long
264    x,
265    y;
266
267  const PixelPacket
268    *p;
269
270  PixelPacket
271    *q;
272
273  destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
274  if (destination  == (Image *) NULL)
275    { /* an exception was thrown */ }
276  for (y=0; y &lt; (long) source-&gt;rows; y++)
277  {
278    p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
279    q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
280    if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
281      break;
282    for (x=0; x &lt; (long) source-&gt;columns; x++)
283    {
284      q-&gt;red=90*p-&gt;red/100;
285      q-&gt;green=90*p-&gt;green/100;
286      q-&gt;blue=90*p-&gt;blue/100;
287      q-&gt;opacity=90*p-&gt;opacity/100;
288      p++;
289      q++;
290    }
291    if (SyncAuthenticPixels(destination,exception) == MagickFalse)
292      break;
293  }
294  if (y &lt; (long) source-&gt;rows)
295    { /* an exception was thrown */ }
296</pre>
297</div>
298
299<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>
300
301<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>
302
303<pre class="code">
304  const IndexPacket
305    *indexes;
306
307  for (y=0; y &lt; (long) source-&gt;rows; y++)
308  {
309    p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
310    if (p == (const PixelPacket *) NULL)
311      break;
312    indexes=GetVirtualIndexes(source);
313    for (x=0; x &lt; (long) source-&gt;columns; x++)
314      (void) printf("%d\n",indexes[x];
315  }
316  if (y &lt; (long) source-&gt;rows)
317    /* an exception was thrown */
318</pre>
319
320<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 but if you ask for 641 pixels, an exception is returned.  GetVirtualPixels() does not have this constraint.  For example,</p>
321
322<pre class="code">
323  p=GetVirtualPixels(source,-3,3,source-&gt;columns+7,7,exception);
324</pre>
325
326<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
327</div>
328
329<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
330<div class="doc-section">
331
332 <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>
333
334<pre class="text">
335  background:           the area surrounding the image is the background color
336  black:                the area surrounding the image is black
337  checker-tile:         alternate squares with image and background color
338  dither:               non-random 32x32 dithered pattern
339  edge:                 extend the edge pixel toward infinity
340  gray:                 the area surrounding the image is gray
341  horizontal-tile:      horizontally tile the image, background color above/below
342  horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
343  mirror:               mirror tile the image
344  random:               choose a random pixel from the image
345  tile:                 tile the image (default)
346  transparent:          the area surrounding the image is transparent blackness
347  vertical-tile:        vertically tile the image, sides are background color
348  vertical-tile-edge:   vertically tile the image and replicate the side edge pixels
349  white:                the area surrounding the image is white
350</pre>
351
352<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>
353</div>
354
355<h3>Cache Storage and Resource Requirements</h3>
356<div class="doc-section">
357
358<p>We mentioned previously 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're 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>
359
360<dl class="doc">
361  <dt class="doc">files</dt>
362  <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>
363  <dt class="doc">area</dt>
364  <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>
365  <dt class="doc">memory</dt>
366  <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
367  <dt class="doc">map</dt>
368  <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
369  <dt class="doc">disk</dt>
370  <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>
371</dl>
372
373<p>To determine the current setting of these limits, use this command:</p>
374
375<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
376------------------------------------------------------------------------
377 768   11.551GiB   8.6631GiB   23.102GiB       16EiB       8   unlimited</pre></span></p>
378<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>
379
380<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>
381</div>
382
383<h3>Cache Views</h3>
384<div class="doc-section">
385
386<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>
387
388<pre class="code">
389  CacheView
390    *view_1,
391    *view_2;
392
393  view_1=OpenCacheView(source);
394  view_2=OpenCacheView(source);
395  for (y=0; y &lt; (long) source-&gt;rows; y++)
396  {
397    u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
398    v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,exception);
399    if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
400      break;
401    for (x=0; x &lt; (long) source-&gt;columns; x++)
402    {
403      /* do something with u &amp; v here */
404    }
405  }
406  view_1=CloseCacheView(view_1);
407  view_2=CloseCacheView(view_2);
408  if (y &lt; (long) source-&gt;rows)
409    { /* an exception was thrown */ }
410</pre>
411</div>
412
413<h3>Magick Persistent Cache Format</h3>
414<div class="doc-section">
415
416<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 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>
417</div>
418
419<h3>Best Practices</h3>
420<div class="doc-section">
421
422<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>
423
424<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>
425
426<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>
427
428<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>
429
430<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>
431
432<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>
433
434<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>
435
436<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 so some algorithms may perform differently than  the non-HDRI version.</p>
437
438<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>
439
440<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>export MAGICK_TEMPORARY_PATH=/data/magick</span></p>
441
442<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>
443
444<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>
445<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>
446</div>
447
448</div>
449
450<h2><a name="stream"></a>Streaming Pixels</h2>
451<div class="doc-section">
452
453<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>
454
455<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>
456
457<pre class="code">
458static size_t StreamHandler(const Image *image,const void *pixels,
459  const size_t columns)
460{
461  /* process pixels here */
462  return(columns);
463}
464
465...
466/* invoke the pixel stream here */
467image=ReadStream(image_info,&amp;StreamHandler,exception);
468</pre>
469
470<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>
471
472</div>
473
474<h2><a name="properties"></a>Image Properties and Profiles</h2>
475<div class="doc-section">
476
477<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>
478
479<pre class="code">
480  (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
481</pre>
482
483<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>
484
485<pre class="code">
486  const char
487    *comment;
488
489  (void) SetImageProperty(image,"comment","This space for rent");
490  comment=GetImageProperty(image,"comment");
491  if (comment == (const char *) NULL)
492    (void) printf("Image comment: %s\n",comment);
493</pre>
494
495<p>Image profiles are handled with <a href="../www/api/profile.html#GetImageProfile">GetImageProfile()</a>, <a href="../www/api/profile.html#SetImageProfile">SetImageProfile()</a>, and <a href="../www/api/profile.html#ProfileImage">ProfileImage()</a> methods.  Here we set a profile and fetch it right back:</p>
496
497<pre class="code">
498  StringInfo
499    *profile;
500
501  profile=AcquireStringInfo(length);
502  SetStringInfoDatum(profile,my_exif_profile);
503  (void) SetImageProfile(image,"EXIF",profile);
504  DestroyStringInfo(profile);
505  profile=GetImageProfile(image,"EXIF");
506  if (profile != (StringInfo *) NULL)
507    (void) PrintStringInfo(stdout,"EXIF",profile);
508</pre>
509
510</div>
511
512<h2><a name="threads"></a>Threads of Execution</h2>
513<div class="doc-section">
514
515<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>
516
517<p>Here is an example of how ImageMagick can take advantage of threads of execution with the OpenMP programming paradigm:</p>
518
519<div class="viewport">
520<pre class="code">
521{
522  CacheView
523    *image_view;
524
525  long
526    y;
527
528  MagickBooleanType
529    status;
530
531  status=MagickTrue;
532  image_view=AcquireCacheView(image);
533  #pragma omp parallel for schedule(dynamic,4) shared(status)
534  for (y=0; y &lt; (long) image-&gt;rows; y++)
535  {
536    register IndexPacket
537      *indexes;
538
539    register long
540      x;
541
542    register PixelPacket
543      *q;
544
545    if (status == MagickFalse)
546      continue;
547    q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
548    if (q == (PixelPacket *) NULL)
549      {
550        status=MagickFalse;
551        continue;
552      }
553    indexes=GetCacheViewAuthenticIndexQueue(image_view);
554    for (x=0; x &lt; (long) image-&gt;columns; x++)
555    {
556      q-&gt;red= ...
557      q-&gt;green= ...
558      q-&gt;blue= ...
559      q-&gt;opacity= ...
560      if (indexes != (IndexPacket *) NULL)
561        indexes[x]= ...
562      q++;
563    }
564    if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
565      status=MagickFalse;
566  }
567  image_view=DestroyCacheView(image_view);
568  if (status == MagickFalse)
569    perror("something went wrong");
570}
571</pre>
572</div>
573
574<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>
575
576</div>
577
578<h2><a name="coders"></a>Custom Image Coders</h2>
579<div class="doc-section">
580
581<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>
582
583<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>
584
585<div class="viewport">
586<pre class="code">
587/*
588  Include declarations.
589*/
590#include "magick/studio.h"
591#include "magick/blob.h"
592#include "magick/blob-private.h"
593#include "magick/colorspace.h"
594#include "magick/exception.h"
595#include "magick/exception-private.h"
596#include "magick/image.h"
597#include "magick/image-private.h"
598#include "magick/list.h"
599#include "magick/magick.h"
600#include "magick/memory_.h"
601#include "magick/monitor.h"
602#include "magick/monitor-private.h"
603#include "magick/quantum-private.h"
604#include "magick/static.h"
605#include "magick/string_.h"
606#include "magick/module.h"
607
608/*
609  Forward declarations.
610*/
611static MagickBooleanType
612  WriteMGKImage(const ImageInfo *,Image *);
613
614/*
615%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
616%                                                                             %
617%                                                                             %
618%                                                                             %
619%   I s M G K                                                                 %
620%                                                                             %
621%                                                                             %
622%                                                                             %
623%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
624%
625%  IsMGK() returns MagickTrue if the image format type, identified by the
626%  magick string, is MGK.
627%
628%  The format of the IsMGK method is:
629%
630%      MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
631%
632%  A description of each parameter follows:
633%
634%    o magick: This string is generally the first few bytes of an image file
635%      or blob.
636%
637%    o length: Specifies the length of the magick string.
638%
639*/
640static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
641{
642  if (length &lt; 7)
643    return(MagickFalse);
644  if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
645    return(MagickTrue);
646  return(MagickFalse);
647}
648
649/*
650%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
651%                                                                             %
652%                                                                             %
653%                                                                             %
654%   R e a d M G K I m a g e                                                   %
655%                                                                             %
656%                                                                             %
657%                                                                             %
658%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
659%
660%  ReadMGKImage() reads a MGK image file and returns it.  It allocates
661%  the memory necessary for the new Image structure and returns a pointer to
662%  the new image.
663%
664%  The format of the ReadMGKImage method is:
665%
666%      Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
667%
668%  A description of each parameter follows:
669%
670%    o image_info: the image info.
671%
672%    o exception: return any errors or warnings in this structure.
673%
674*/
675static Image *ReadMGKImage(const ImageInfo *image_info,
676  ExceptionInfo *exception)
677{
678  char
679    buffer[MaxTextExtent];
680
681  Image
682    *image;
683
684  long
685    y;
686
687  MagickBooleanType
688    status;
689
690  register long
691    x;
692
693  register PixelPacket
694    *q;
695
696  register unsigned char
697    *p;
698
699  ssize_t
700    count;
701
702  unsigned char
703    *pixels;
704
705  unsigned long
706    columns,
707    rows;
708
709  /*
710    Open image file.
711  */
712  assert(image_info != (const ImageInfo *) NULL);
713  assert(image_info-&gt;signature == MagickSignature);
714  if (image_info-&gt;debug != MagickFalse)
715    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
716  assert(exception != (ExceptionInfo *) NULL);
717  assert(exception-&gt;signature == MagickSignature);
718  image=AcquireImage(image_info);
719  status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
720  if (status == MagickFalse)
721    {
722      image=DestroyImageList(image);
723      return((Image *) NULL);
724    }
725  /*
726    Read MGK image.
727  */
728  (void) ReadBlobString(image,buffer);  /* read magic number */
729  if (IsMGK(buffer,7) == MagickFalse)
730    ThrowReaderException(CorruptImageError,"ImproperImageHeader");
731  (void) ReadBlobString(image,buffer);
732  count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
733  if (count &lt;= 0)
734    ThrowReaderException(CorruptImageError,"ImproperImageHeader");
735  do
736  {
737    /*
738      Initialize image structure.
739    */
740    image-&gt;columns=columns;
741    image-&gt;rows=rows;
742    image-&gt;depth=8;
743    if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
744      if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
745        break;
746    /*
747      Convert MGK raster image to pixel packets.
748    */
749    if (SetImageExtent(image,0,0) == MagickFalse)
750      {
751        InheritException(exception,&amp;image-&gt;exception);
752        return(DestroyImageList(image));
753      }
754    pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
755    if (pixels == (unsigned char *) NULL)
756      ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
757    for (y=0; y &lt; (long) image-&gt;rows; y++)
758    {
759      count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
760      if (count != (ssize_t) (3*image-&gt;columns))
761        ThrowReaderException(CorruptImageError,"UnableToReadImageData");
762      p=pixels;
763      q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
764      if (q == (PixelPacket *) NULL)
765        break;
766      for (x=0; x &lt; (long) image-&gt;columns; x++)
767      {
768        q-&gt;red=ScaleCharToQuantum(*p++);
769        q-&gt;green=ScaleCharToQuantum(*p++);
770        q-&gt;blue=ScaleCharToQuantum(*p++);
771        q++;
772      }
773      if (SyncAuthenticPixels(image,exception) == MagickFalse)
774        break;
775      if ((image-&gt;previous == (Image *) NULL) &&
776          (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
777        break;
778    }
779    pixels=(unsigned char *) RelinquishMagickMemory(pixels);
780    if (EOFBlob(image) != MagickFalse)
781      {
782        ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
783        break;
784      }
785    /*
786      Proceed to next image.
787    */
788    if (image_info-&gt;number_scenes != 0)
789      if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
790        break;
791    *buffer='\0';
792    (void) ReadBlobString(image,buffer);
793    count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
794    if (count != 0)
795      {
796        /*
797          Allocate next image structure.
798        */
799        AcquireNextImage(image_info,image);
800        if (GetNextImageInList(image) == (Image *) NULL)
801          {
802            image=DestroyImageList(image);
803            return((Image *) NULL);
804          }
805        image=SyncNextImageInList(image);
806        status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
807        if (status == MagickFalse)
808          break;
809      }
810  } while (count != 0);
811  (void) CloseBlob(image);
812  return(GetFirstImageInList(image));
813}
814
815/*
816%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
817%                                                                             %
818%                                                                             %
819%                                                                             %
820%   R e g i s t e r M G K I m a g e                                           %
821%                                                                             %
822%                                                                             %
823%                                                                             %
824%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
825%
826%  RegisterMGKImage() adds attributes for the MGK image format to
827%  the list of supported formats.  The attributes include the image format
828%  tag, a method to read and/or write the format, whether the format
829%  supports the saving of more than one frame to the same file or blob,
830%  whether the format supports native in-memory I/O, and a brief
831%  description of the format.
832%
833%  The format of the RegisterMGKImage method is:
834%
835%      unsigned long RegisterMGKImage(void)
836%
837*/
838ModuleExport unsigned long RegisterMGKImage(void)
839{
840  MagickInfo
841    *entry;
842
843  entry=SetMagickInfo("MGK");
844  entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
845  entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
846  entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
847  entry-&gt;description=ConstantString("MGK");
848  entry-&gt;module=ConstantString("MGK");
849  (void) RegisterMagickInfo(entry);
850  return(MagickImageCoderSignature);
851}
852
853/*
854%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
855%                                                                             %
856%                                                                             %
857%                                                                             %
858%   U n r e g i s t e r M G K I m a g e                                       %
859%                                                                             %
860%                                                                             %
861%                                                                             %
862%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
863%
864%  UnregisterMGKImage() removes format registrations made by the
865%  MGK module from the list of supported formats.
866%
867%  The format of the UnregisterMGKImage method is:
868%
869%      UnregisterMGKImage(void)
870%
871*/
872ModuleExport void UnregisterMGKImage(void)
873{
874  (void) UnregisterMagickInfo("MGK");
875}
876
877/*
878%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
879%                                                                             %
880%                                                                             %
881%                                                                             %
882%   W r i t e M G K I m a g e                                                 %
883%                                                                             %
884%                                                                             %
885%                                                                             %
886%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
887%
888%  WriteMGKImage() writes an image to a file in red, green, and blue
889%  MGK rasterfile format.
890%
891%  The format of the WriteMGKImage method is:
892%
893%      MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
894%
895%  A description of each parameter follows.
896%
897%    o image_info: the image info.
898%
899%    o image:  The image.
900%
901*/
902static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
903{
904  char
905    buffer[MaxTextExtent];
906
907  long
908    y;
909
910  MagickBooleanType
911    status;
912
913  MagickOffsetType
914    scene;
915
916  register const PixelPacket
917    *p;
918
919  register long
920    x;
921
922  register unsigned char
923    *q;
924
925  unsigned char
926    *pixels;
927
928  /*
929    Open output image file.
930  */
931  assert(image_info != (const ImageInfo *) NULL);
932  assert(image_info-&gt;signature == MagickSignature);
933  assert(image != (Image *) NULL);
934  assert(image-&gt;signature == MagickSignature);
935  if (image-&gt;debug != MagickFalse)
936    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
937  status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
938  if (status == MagickFalse)
939    return(status);
940  scene=0;
941  do
942  {
943    /*
944      Allocate memory for pixels.
945    */
946    if (image-&gt;colorspace != RGBColorspace)
947      (void) SetImageColorspace(image,RGBColorspace);
948    pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
949      3UL*sizeof(*pixels));
950    if (pixels == (unsigned char *) NULL)
951      ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
952    /*
953      Initialize raster file header.
954    */
955    (void) WriteBlobString(image,"id=mgk\n");
956    (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
957      image-&gt;columns,image-&gt;rows);
958    (void) WriteBlobString(image,buffer);
959    for (y=0; y &lt; (long) image-&gt;rows; y++)
960    {
961      p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
962      if (p == (const PixelPacket *) NULL)
963        break;
964      q=pixels;
965      for (x=0; x &lt; (long) image-&gt;columns; x++)
966      {
967        *q++=ScaleQuantumToChar(p-&gt;red);
968        *q++=ScaleQuantumToChar(p-&gt;green);
969        *q++=ScaleQuantumToChar(p-&gt;blue);
970        p++;
971      }
972      (void) WriteBlob(image,(size_t) (q-pixels),pixels);
973      if ((image-&gt;previous == (Image *) NULL) &&
974          (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
975        break;
976    }
977    pixels=(unsigned char *) RelinquishMagickMemory(pixels);
978    if (GetNextImageInList(image) == (Image *) NULL)
979      break;
980    image=SyncNextImageInList(image);
981    status=SetImageProgress(image,SaveImagesTag,scene,
982      GetImageListLength(image));
983    if (status == MagickFalse)
984      break;
985    scene++;
986  } while (image_info-&gt;adjoin != MagickFalse);
987  (void) CloseBlob(image);
988  return(MagickTrue);
989}
990</pre>
991</div>
992
993<p>To invoke the custom coder from the command line, use these commands:</p>
994
995<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>
996<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>
997
998</div>
999
1000<h2><a name="filters"></a>Custom Image Filters</h2>
1001<div class="doc-section">
1002
1003<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>
1004
1005<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>
1006
1007<div class="viewport">
1008<pre class="code">
1009#include &lt;stdio.h>
1010#include &lt;stdlib.h>
1011#include &lt;string.h>
1012#include &lt;time.h>
1013#include &lt;assert.h>
1014#include &lt;math.h>
1015#include "magick/MagickCore.h"
1016
1017/*
1018%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1019%                                                                             %
1020%                                                                             %
1021%                                                                             %
1022%   a n a l y z e I m a g e                                                   %
1023%                                                                             %
1024%                                                                             %
1025%                                                                             %
1026%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1027%
1028%  analyzeImage() computes the brightness and saturation mean, standard
1029%  deviation, kurtosis and skewness and stores these values as properties of
1030%  the image.
1031%
1032%  The format of the analyzeImage method is:
1033%
1034%      unsigned long analyzeImage(Image *images,const int argc,
1035%        const char **argv,ExceptionInfo *exception)
1036%
1037%  A description of each parameter follows:
1038%
1039%    o image: the address of a structure of type Image.
1040%
1041%    o argc: Specifies a pointer to an integer describing the number of
1042%      elements in the argument vector.
1043%
1044%    o argv: Specifies a pointer to a text array containing the command line
1045%      arguments.
1046%
1047%    o exception: return any errors or warnings in this structure.
1048%
1049*/
1050ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1051  const char **argv,ExceptionInfo *exception)
1052{
1053  CacheView
1054    *image_view;
1055
1056  char
1057    text[MaxTextExtent];
1058
1059  double
1060    area,
1061    brightness_mean,
1062    brightness_standard_deviation,
1063    brightness_kurtosis,
1064    brightness_skewness,
1065    brightness_sum_x,
1066    brightness_sum_x2,
1067    brightness_sum_x3,
1068    brightness_sum_x4,
1069    saturation_mean,
1070    saturation_standard_deviation,
1071    saturation_kurtosis,
1072    saturation_skewness,
1073    saturation_sum_x,
1074    saturation_sum_x2,
1075    saturation_sum_x3,
1076    saturation_sum_x4;
1077
1078  double
1079    brightness,
1080    hue,
1081    saturation;
1082
1083  Image
1084    *image;
1085
1086  long
1087    y;
1088
1089  register const PixelPacket
1090    *p;
1091
1092  register long
1093    x;
1094
1095  assert(images != (Image **) NULL);
1096  assert(*images != (Image *) NULL);
1097  assert((*images)->signature == MagickSignature);
1098  (void) argc;
1099  (void) argv;
1100  image=(*images);
1101  for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1102  {
1103    brightness_sum_x=0.0;
1104    brightness_sum_x2=0.0;
1105    brightness_sum_x3=0.0;
1106    brightness_sum_x4=0.0;
1107    brightness_mean=0.0;
1108    brightness_standard_deviation=0.0;
1109    brightness_kurtosis=0.0;
1110    brightness_skewness=0.0;
1111    saturation_sum_x=0.0;
1112    saturation_sum_x2=0.0;
1113    saturation_sum_x3=0.0;
1114    saturation_sum_x4=0.0;
1115    saturation_mean=0.0;
1116    saturation_standard_deviation=0.0;
1117    saturation_kurtosis=0.0;
1118    saturation_skewness=0.0;
1119    area=0.0;
1120    image_view=AcquireCacheView(image);
1121    for (y=0; y &lt; (long) image-&gt;rows; y++)
1122    {
1123      p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1124      if (p == (const PixelPacket *) NULL)
1125        break;
1126      for (x=0; x &lt; (long) image-&gt;columns; x++)
1127      {
1128        ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1129        brightness*=QuantumRange;
1130        brightness_sum_x+=brightness;
1131        brightness_sum_x2+=brightness*brightness;
1132        brightness_sum_x3+=brightness*brightness*brightness;
1133        brightness_sum_x4+=brightness*brightness*brightness*brightness;
1134        saturation*=QuantumRange;
1135        saturation_sum_x+=saturation;
1136        saturation_sum_x2+=saturation*saturation;
1137        saturation_sum_x3+=saturation*saturation*saturation;
1138        saturation_sum_x4+=saturation*saturation*saturation*saturation;
1139        area++;
1140        p++;
1141      }
1142    }
1143    image_view=DestroyCacheView(image_view);
1144    if (area &lt;= 0.0)
1145      break;
1146    brightness_mean=brightness_sum_x/area;
1147    (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1148    (void) SetImageProperty(image,"filter:brightness:mean",text);
1149    brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1150      area*brightness_sum_x/area));
1151    (void) FormatMagickString(text,MaxTextExtent,"%g",
1152      brightness_standard_deviation);
1153    (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1154    if (brightness_standard_deviation != 0)
1155      brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1156        brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1157        brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1158        brightness_mean*brightness_mean)/(brightness_standard_deviation*
1159        brightness_standard_deviation*brightness_standard_deviation*
1160        brightness_standard_deviation)-3.0;
1161    (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1162    (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1163    if (brightness_standard_deviation != 0)
1164      brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1165        brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1166        brightness_mean)/(brightness_standard_deviation*
1167        brightness_standard_deviation*brightness_standard_deviation);
1168    (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1169    (void) SetImageProperty(image,"filter:brightness:skewness",text);
1170    saturation_mean=saturation_sum_x/area;
1171    (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1172    (void) SetImageProperty(image,"filter:saturation:mean",text);
1173    saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1174      area*saturation_sum_x/area));
1175    (void) FormatMagickString(text,MaxTextExtent,"%g",
1176      saturation_standard_deviation);
1177    (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1178    if (saturation_standard_deviation != 0)
1179      saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1180        saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1181        saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1182        saturation_mean*saturation_mean)/(saturation_standard_deviation*
1183        saturation_standard_deviation*saturation_standard_deviation*
1184        saturation_standard_deviation)-3.0;
1185    (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1186    (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1187    if (saturation_standard_deviation != 0)
1188      saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1189        saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1190        saturation_mean)/(saturation_standard_deviation*
1191        saturation_standard_deviation*saturation_standard_deviation);
1192    (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1193    (void) SetImageProperty(image,"filter:saturation:skewness",text);
1194  }
1195  return(MagickImageFilterSignature);
1196}
1197</pre>
1198</div>
1199
1200<p>To invoke the custom filter from the command line, use this command:</p>
1201
1202<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/>
1203    Format: LOGO (ImageMagick Logo)  <br/>
1204    Class: PseudoClass  <br/>
1205    Geometry: 640x480  <br/>
1206    ...  <br/>
1207    filter:brightness:kurtosis: 8.98864 <br/>
1208    filter:brightness:mean: 238.096 <br/>
1209    filter:brightness:skewness: -3.04519 <br/>
1210    filter:brightness:standard-deviation: 46.3286 <br/>
1211    filter:saturation:kurtosis: 5.9137 <br/>
1212    filter:saturation:mean: 23.4635 <br/>
1213    filter:saturation:skewness: 2.71874 <br/>
1214    filter:saturation:standard-deviation: 64.7734</span></p>
1215
1216<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>
1217
1218</div>
1219
1220</div>
1221
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