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157 <p class="navigation-index">[<a href="#overview">Architecture Overview</a> • <a href="#cache">The Pixel Cache</a> • <a href="#stream">Streaming Pixels</a> • <a href="#properties">Image Properties and Profiles</a> • <a href="#tera-pixel">Large Image Support</a> • <a href="#threads">Threads of Execution</a> • <a href="#distributed">Heterogeneous Distributed Processing</a> • <a href="#coders">Custom Image Coders</a> • <a href="#filters">Custom Image Filters</a>]</p>
159 <div class="doc-section">
160 <p>The citizens of Oz were quite content with their benefactor, the all-powerful Wizard. They accepted his wisdom and benevolence without ever questioning the who, why, and where of his power. Like the citizens of Oz, if you feel comfortable that ImageMagick can help you convert, edit, or compose your images without knowing what goes on behind the curtain, feel free to skip this section. However, if you want to know more about the software and algorithms behind ImageMagick, read on. To fully benefit from this discussion, you should be comfortable with image nomenclature and be familiar with computer programming.</p>
163 <h2><a name="overview"></a>Architecture Overview</h2>
164 <div class="doc-section">
166 <p>An image typically consists of a rectangular region of pixels and metadata. To convert, edit, or compose an image in an efficient manner we need convenient access to any pixel anywhere within the region (and sometimes outside the region). And in the case of an image sequence, we need access to any pixel of any region of any image in the sequence. However, there are hundreds of image formats such JPEG, TIFF, PNG, GIF, etc., that makes it difficult to access pixels on demand. Within these formats we find differences in:</p>
169 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
170 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
171 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
172 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
173 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
174 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
177 <p>In addition, some image pixels may require attenuation, some formats permit more than one frame, and some formats contain vector graphics that must first be rasterized (converted from vector to pixels).</p>
179 <p>An efficient implementation of an image processing algorithm may require we get or set:</p>
182 <li>one pixel a time (e.g. pixel at location 10,3)</li>
183 <li>a single scanline (e.g. all pixels from row 4)</li>
184 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
185 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
186 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
187 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
188 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
189 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
190 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
191 <li>a high-dynamic range pixel that can include negative values as well as values that exceed the quantum depth (e.g. -0.00716)</li>
192 <li>one or more pixels simultaneously in different threads of execution</li>
193 <li>all the pixels in memory to take advantage of speed-ups offered by executing in concert across heterogeneous platforms consisting of CPUs, GPUs, and other processors</li>
196 <p>In addition, some images include a clip mask that define which pixels are eligible to be updated. Pixels outside the area defined by the clip mask remain untouched.</p>
198 <p>Given the varied image formats and image processing requirements, we implemented the ImageMagick <a href="#cache">pixel cache</a> to provide convenient sequential or parallel access to any pixel on demand anywhere inside the image region (we call these <a href="#authentic-pixels">authentic pixels</a>) and from any image in a sequence. In addition, the pixel cache permits access to pixels outside the boundaries defined by the image (we call these <a href="#virtual-pixels">virtual pixels</a>).</p>
200 <p>In addition to pixels, images have a plethora of <a href="#properties">image properties and profiles</a>. Properties include the well known attributes such as width, height, depth, and colorspace. An image may have optional properties which might include the image author, a comment, a create date, and others. Some images also include profiles for color management, or EXIF, IPTC, 8BIM, or XMP informational profiles. ImageMagick provides command line options and programming methods to get, set, or view image properties or profiles or apply profiles.</p>
202 <p>ImageMagick consists of more than 400,000 lines of C code and optionally depends on several million lines of code in dependent libraries (e.g. JPEG, PNG, TIFF libraries). Given that, one might expect a huge architecture document. However, a great majority of image processing is simply accessing pixels and its metadata and our simple and elegant implementation makes this easy for the ImageMagick developer. We discuss the implementation of the pixel cache and getting and setting image properties and profiles in the next few sections. Next, we discuss using ImageMagick within a <a href="#threads">thread</a> of execution. In the final sections, we discuss <a href="#coders">image coders</a> to read or write a particular image format followed by a few words on creating a <a href="#filters">filter</a> to access or update pixels based on your custom requirements.</p>
206 <h2><a name="cache"></a>The Pixel Cache</h2>
207 <div class="doc-section">
209 <p>The ImageMagick pixel cache is a repository for image pixels with up to 5 channels. The first 4 channels are stored contiguously and an optional second area follows with 1 channel. The channels are at the depth specified when ImageMagick was built. The channel depths are 8 bits-per-pixel component for the Q8 version of ImageMagick, 16 bits-per-pixel component for the Q16 version, and 32 bits-per-pixel component for the Q32 version. By default pixel components are unsigned quantities, however, if you use the <a href="../www/high-dynamic-range.html">high dynamic-range</a> version of ImageMagick, the components are 32-bit floating point. The primary 4 channels can hold any value but typically contain red, green, blue, and alpha intensities or cyan, magenta, yellow, and alpha intensities. The optional fifth channel contains the colormap indexes for colormapped images or the black channel for CMYK images. The pixel cache storage may be heap memory, anonymous memory mapped memory, disk-backed memory mapped, or on disk. The pixel cache is reference-counted. Only the cache properties are copied when the cache is cloned. The cache pixels are subsequently copied when you signal your intention to update any of the pixels.</p>
211 <h3>Create the Pixel Cache</h3>
212 <div class="doc-section">
214 <p>The pixel cache is associated with an image when it is created and it is initialized when you try to get or put pixels. Here are three common methods to associate a pixel cache with an image:</p>
216 <h4>Create an image canvas initialized to the background color:</h4>
218 image=AllocateImage(image_info);
219 if (SetImageExtent(image,640,480) == MagickFalse)
220 { /* an exception was thrown */ }
221 (void) QueryMagickColor("red",&image->background_color,&image->exception);
222 SetImageBackgroundColor(image);
225 <h4>Create an image from a JPEG image on disk:</h4>
226 <p class="code"> (void) strcpy(image_info->filename,"image.jpg"):
227 image=ReadImage(image_info,exception);
228 if (image == (Image *) NULL)
229 { /* an exception was thrown */ }
231 <h4>Create an image from a memory based image:</h4>
233 image=BlobToImage(blob_info,blob,extent,exception);
234 if (image == (Image *) NULL)
235 { /* an exception was thrown */ }
238 <p>In our discussion of the pixel cache, we use the <a href="../www/magick-core.html">MagickCore API</a> to illustrate our points, however, the principles are the same for other program interfaces to ImageMagick.</p>
240 <p>When the pixel cache is initialized, pixels are scaled from whatever bit depth they originated from to that required by the pixel cache. For example, a 1-channel 1-bit monochrome PBM image is scaled to a 4 channel 8-bit RGBA image, if you are using the Q8 version of ImageMagick, and 16-bit RGBA for the Q16 version. You can determine which version you have with the <a href="../www/command-line-options.html#version">‑version</a> option: </p>
242 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.2-10 2010-104-105 Q16 http://www.imagemagick.org</span></p>
243 <p>As you can see, the convenience of the pixel cache sometimes comes with a trade-off in storage (e.g. storing a 1-bit monochrome image as 16-bit RGBA is wasteful) and speed (i.e. storing the entire image in memory is generally slower than accessing one scanline of pixels at a time). In most cases, the benefits of the pixel cache typically outweigh any disadvantages.</p>
246 <h3><a name="authentic-pixels"></a>Access the Pixel Cache</h3>
247 <div class="doc-section">
249 <p>Once the pixel cache is associated with an image, you typically want to get, update, or put pixels into it. We refer to pixels inside the image region as <em>authentic pixels</em> and outside the region as <em>virtual pixels</em>. Use these methods to access the pixels in the cache:</p>
251 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify</li>
252 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
253 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
254 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
257 <p>Here is a typical <a href="../www/magick-core.html">MagickCore</a> code snippet for manipulating pixels in the pixel cache. In our example, we copy pixels from the input image to the output image and decrease the intensity by 10%:</p>
259 <div class="viewport">
271 destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
272 if (destination == (Image *) NULL)
273 { /* an exception was thrown */ }
274 for (y=0; y < (long) source->rows; y++)
276 p=GetVirtualPixels(source,0,y,source->columns,1,exception);
277 q=GetAuthenticPixels(destination,0,y,destination->columns,1,exception);
278 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
280 for (x=0; x < (long) source->columns; x++)
282 q->red=90*p->red/100;
283 q->green=90*p->green/100;
284 q->blue=90*p->blue/100;
285 q->opacity=90*p->opacity/100;
289 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
292 if (y < (long) source->rows)
293 { /* an exception was thrown */ }
297 <p>When we first create the destination image by cloning the source image, the pixel cache pixels are not copied. They are only copied when you signal your intentions to modify the pixel cache by calling <a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> or <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a>. Use <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> if you want to set new pixel values rather than update existing ones. Finally, use <a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p>
299 <p>Recall how we mentioned that the indexes of a colormapped image or the black channel of a CMYK image are stored separately. Use <a href="../www/api/cache.html#GetVirtualIndexes">GetVirtualIndexes()</a> (to read the indexes) or <a href="../www/api/cache.html#GetAuthenticIndexes">GetAuthenticIndexes()</a> (to update the indexes) to gain access to this channel. For example, to print the colormap indexes, use:</p>
305 for (y=0; y < (long) source->rows; y++)
307 p=GetVirtualPixels(source,0,y,source->columns,1);
308 if (p == (const PixelPacket *) NULL)
310 indexes=GetVirtualIndexes(source);
311 for (x=0; x < (long) source->columns; x++)
312 (void) printf("%d\n",indexes[x];
314 if (y < (long) source->rows)
315 /* an exception was thrown */
318 <p>The pixel cache manager decides whether to give you direct or indirect access to the image pixels. In some cases the pixels are staged to an intermediate buffer-- and that is why you must call SyncAuthenticPixels() to ensure this buffer is <em>pushed</em> out to the pixel cache to guarantee the corresponding pixels in the cache are updated. For this reason we recommend that you only read or update a scanline or a few scanlines of pixels at a time. However, you can get any rectangular region of pixels you want. GetAuthenticPixels() requires that the region you request is within the bounds of the image area. For a 640 by 480 image, you can get a scanline of 640 pixels at row 479 but if you ask for a scanline at row 480, an exception is returned (rows are numbered starting at 0). GetVirtualPixels() does not have this constraint. For example,</p>
321 p=GetVirtualPixels(source,-3,3,source->columns+7,7,exception);
324 <p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
327 <h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
328 <div class="doc-section">
330 <p>There are a plethora of image processing algorithms that require a neighborhood of pixels about a pixel of interest. The algorithm typically includes a caveat concerning how to handle pixels around the image boundaries, known as edge pixels. With virtual pixels, you do not need to concern yourself about special edge processing other than choosing which virtual pixel method is most appropriate for your algorithm.</p>
331 <p>Access to the virtual pixels are controlled by the <a href="../www/api/cache.html#SetImageVirtualPixelMethod">SetImageVirtualPixelMethod()</a> method from the MagickCore API or the <a href="../www/command-line-options.html#virtual-pixel">‑virtual‑pixel</a> option from the command line. The methods include:</p>
334 background: the area surrounding the image is the background color
335 black: the area surrounding the image is black
336 checker-tile: alternate squares with image and background color
337 dither: non-random 32x32 dithered pattern
338 edge: extend the edge pixel toward infinity
339 gray: the area surrounding the image is gray
340 horizontal-tile: horizontally tile the image, background color above/below
341 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
342 mirror: mirror tile the image
343 random: choose a random pixel from the image
344 tile: tile the image (default)
345 transparent: the area surrounding the image is transparent blackness
346 vertical-tile: vertically tile the image, sides are background color
347 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
348 white: the area surrounding the image is white
353 <h3>Cache Storage and Resource Requirements</h3>
354 <div class="doc-section">
356 <p>Recall that this simple and elegant design of the ImageMagick pixel cache comes at a cost in terms of storage and processing speed. The pixel cache storage requirements scales with the area of the image and the bit depth of the pixel components. For example, if we have a 640 by 480 image and we are using the Q16 version of ImageMagick, the pixel cache consumes image <em>width * height * bit-depth / 8 * channels</em> bytes or approximately 2.3 mebibytes (i.e. 640 * 480 * 2 * 4). Not too bad, but what if your image is 25000 by 25000 pixels? The pixel cache requires approximately 4.7 gibibytes of storage. Ouch. ImageMagick accounts for possible huge storage requirements by caching large images to disk rather than memory. Typically the pixel cache is stored in memory using heap memory. If heap memory is exhausted, pixels are stored in in an anonymous map; if the anonymous memory map is exhausted, we create the pixel cache on disk and attempt to memory-map it; and if memory-map memory is exhausted, we simply use standard disk I/O. Disk storage is cheap but it is also very slow, upwards of 1000 times slower than memory. We can get some speed improvements, up to 5 times, if we use memory mapping to the disk-based cache. These decisions about storage are made <em>automagically</em> by the pixel cache manager negotiating with the operating system. However, you can influence how the pixel cache manager allocates the pixel cache with <em>cache resource limits</em>. The limits include:</p>
359 <dt class="doc">files</dt>
360 <dd>maximum number of open pixel cache files. When this limit is exceeded, any subsequent pixels cached to disk are closed and reopened on demand. This behavior permits a large number of images to be accessed simultaneously on disk, but with a speed penalty due to repeated open/close calls.</dd>
361 <dt class="doc">area</dt>
362 <dd>maximum area in bytes of any one image that can reside in the pixel cache memory. If this limit is exceeded, the image is automagically cached to disk.</dd>
363 <dt class="doc">memory</dt>
364 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
365 <dt class="doc">map</dt>
366 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
367 <dt class="doc">disk</dt>
368 <dd>maximum amount of disk space in bytes permitted for use by the pixel cache. If this limit is exceeded, the pixel cache is not created and a fatal exception is thrown.</dd>
371 <p>To determine the current setting of these limits, use this command:</p>
373 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>identify -list resource</span><span class='crtout'><pre>File Area Memory Map Disk Thread Time
374 -------------------------------------------------------------------------------
375 768 12.443GB 8.6917GiB 23.178GiB 18.446744EB 8 unlimited</pre></span></p>
376 <p>You can set these limits either with <a href="../www/resources.html#environment">environment variables</a>, the <a href="../www/command-line-options.html#limit">-limit</a> command line option, or the <a href="../www/api/resource.html#SetMagickResourceLimit">SetMagickResourceLimit()</a> MagickCore API method. As an example, our online web interface to ImageMagick, <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">ImageMagick Studio</a>, has an area limit of 64 megabytes, a memory limit of 128 mebibytes and a map limit of 256 mebibytes and a disk limit of 1 gigabytes. Since we process multiple simultaneous sessions, we don't want any one session consuming all the available memory. Instead large images are cached to disk. If the image is too large and exceeds the pixel cache disk limit, the program exits. In addition, we place a 60 second time limit to prevent any run-away processing tasks.</p>
378 <p>Note, the cache limits are global, meaning if you create several images, the combined resource requirements are compared to the limit to determine the pixel cache storage disposition.</p>
382 <div class="doc-section">
384 <p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() from the MagickCore API can only deal with one pixel cache area per image at a time. Suppose you want to access the first and last scanline from the same image at the same time? The solution is to use a <em>cache view</em>. A cache view permits you to access as many areas simultaneously in the pixel cache as you require. The cache view <a href="../www/api/cache-view.html">methods</a> behave like the previous methods except you must first open a view and close it when you are finished with it. Here is a snippet of MagickCore code that permits us to access two areas of an image simultaneously:</p>
391 view_1=OpenCacheView(source);
392 view_2=OpenCacheView(source);
393 for (y=0; y < (long) source->rows; y++)
395 u=GetCacheViewVirtualPixels(view_1,0,y,source->columns,1,exception);
396 v=GetCacheViewVirtualPixels(view_2,0,source->rows-y-1,source->columns,1,exception);
397 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
399 for (x=0; x < (long) source->columns; x++)
401 /* do something with u & v here */
404 view_1=CloseCacheView(view_1);
405 view_2=CloseCacheView(view_2);
406 if (y < (long) source->rows)
407 { /* an exception was thrown */ }
411 <h3>Magick Persistent Cache Format</h3>
412 <div class="doc-section">
414 <p>Recall that each image format is decoded by ImageMagick and the pixels are deposited in the pixel cache. If you write an image, the pixels are read from the pixel cache and encoded as required by the format you are writing (e.g. GIF, PNG, etc.). The Magick Persistent Cache (MPC) format is designed to eliminate the overhead of decoding and encoding pixels to and from an image format. MPC writes two files. One, with the extension <kbd>.mpc</kbd>, retains all the properties associated with the image or image sequence (e.g. width, height, colorspace, etc.) and the second, with the extension <kbd>.cache</kbd>, is the pixel cache in the native raw format. When reading an MPC image file, ImageMagick reads the image properties and memory maps the pixel cache on disk eliminating the need for decoding the image pixels. The tradeoff is in disk space. MPC is generally larger in file size than most other image formats.</p>
417 <h3>Best Practices</h3>
418 <div class="doc-section">
420 <p>Although you can request any pixel from the pixel cache, any block of pixels, any scanline, multiple scanlines, any row, or multiple rows with the GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels, GetCacheViewVirtualPixels(), GetCacheViewAuthenticPixels(), and QueueCacheViewAuthenticPixels() methods, ImageMagick is optimized to return a few pixels or a few pixels rows at time. There are additional optimizations if you request a single scanline or a few scanlines at a time. These methods also permit random access to the pixel cache, however, ImageMagick is optimized for sequential access.</p>
422 <p>If you update pixels returned from GetAuthenticPixels() or GetCacheViewAuthenticPixels(), don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to ensure your changes are synchronized with the pixel cache.</p>
424 <p>Use QueueAuthenticPixels() or QueueCacheViewAuthenticPixels() if you are setting an initial pixel value. The GetAuthenticPixels() or GetCacheViewAuthenticPixels() method reads pixels from the cache and if you are setting an initial pixel value, this read is unnecessary. Don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to push your updates to the pixel cache.</p>
426 <p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() are slightly more efficient than their cache view counter-parts. However, cache views are required if you need access to more than one region of the image simultaneously or if more than one <a href="#threads">thread of execution</a> is accessing the image.</p>
428 <p>You can request pixels outside the bounds of the image with GetVirtualPixels() or GetCacheViewVirtualPixels(), however, it is more efficient to request pixels within the confines of the image region.</p>
430 <p>Although you can force the pixel cache to disk using appropriate resource limits, disk access can be upwards of 1000 times slower than memory access. For fast, efficient, access to the pixel cache, try to keep the pixel cache in heap memory or anonymous mapped memory.</p>
432 <p>The ImageMagick Q16 version of ImageMagick permits you to read and write 16 bit images without scaling but the pixel cache consumes twice as much resources as the Q8 version. If your system has constrained memory or disk resources, consider the Q8 version of ImageMagick. In addition, the Q8 version typically executes faster than the Q16 version.</p>
434 <p>A great majority of image formats and algorithms restrict themselves to a fixed range of pixel values from 0 to some maximum value, for example, the Q16 version of ImageMagick permit intensities from 0 to 65535. High dynamic-range imaging (HDRI), however, permits a far greater dynamic range of exposures (i.e. a large difference between light and dark areas) than standard digital imaging techniques. HDRI accurately represents the wide range of intensity levels found in real scenes ranging from the brightest direct sunlight to the deepest darkest shadows. Enable <a href="../www/high-dynamic-range.html">HDRI</a> at ImageMagick build time to deal with high dynamic-range images, but be mindful that each pixel component is a 32-bit floating point value. In addition, pixel values are not clamped by default so some algorithms may perform differently than the non-HDRI version.</p>
436 <p>If you are dealing with large images, make sure the pixel cache is written to a disk area with plenty of free space. Under Unix, this is typically <kbd>/tmp</kbd> and for Windows, <kbd>c:/temp</kbd>. You can tell ImageMagick to write the pixel cache to an alternate location with the MAGICK_TEMPORARY_PATH environment variable. For example,</p>
438 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>export MAGICK_TEMPORARY_PATH=/data/magick</span></p>
440 <p>If you plan on processing the same image many times, consider the MPC format. Reading a MPC image has near-zero overhead because its in the native pixel cache format eliminating the need for decoding the image pixels. Here is an example:</p>
442 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.tif image.mpc</span><span class='crtout'></span><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.mpc -crop 100x100+0+0 +repage 1.png</span><span class='crtout'></span><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.mpc -crop 100x100+100+0 +repage 2.png</span><span class='crtout'></span><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.mpc -crop 100x100+200+0 +repage 3.png</span></p>
443 <p>MPC is ideal for web sites. It reduces the overhead of reading and writing an image. We use it exclusively at our <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">online image studio</a>.</p>
448 <h2><a name="stream"></a>Streaming Pixels</h2>
449 <div class="doc-section">
451 <p>ImageMagick provides for streaming pixels as they are read from or written to an image. This has several advantages over the pixel cache. The time and resources consumed by the pixel cache scale with the area of an image, whereas the pixel stream resources scale with the width of an image. The disadvantage is the pixels must be consumed as they are streamed so there is no persistence.</p>
453 <p>Use <a href="../www/api/stream.html#ReadStream">ReadStream()</a> or <a href="../www/api/stream.html#WriteStream">WriteStream()</a> with an appropriate callback method in your MagickCore program to consume the pixels as they are streaming. Here's an abbreviated example of using ReadStream:</p>
456 static size_t StreamHandler(const Image *image,const void *pixels,
457 const size_t columns)
459 /* process pixels here */
464 /* invoke the pixel stream here */
465 image=ReadStream(image_info,&StreamHandler,exception);
468 <p>We also provide a lightweight tool, <a name="stream"></a><a href="../www/stream.html">stream</a>, to stream one or more pixel components of the image or portion of the image to your choice of storage formats. It writes the pixel components as they are read from the input image a row at a time making <a name="stream"></a><a href="../www/stream.html">stream</a> desirable when working with large images or when you require raw pixel components.</p>
472 <h2><a name="properties"></a>Image Properties and Profiles</h2>
473 <div class="doc-section">
475 <p>Images have metadata associated with them in the form of properties (e.g. width, height, description, etc.) and profiles (e.g. EXIF, IPTC, color management). ImageMagick provides convenient methods to get, set, or update image properties and get, set, update, or apply profiles. Some of the more popular image properties are associated with the Image structure in the MagickCore API. For example:</p>
478 (void) printf("image width: %lu, height: %lu\n",image->columns,image->rows);
481 <p>For a great majority of image properties, such as an image comment or description, we use the <a href="../www/api/property.html#GetImageProperty">GetImageProperty()</a> and <a href="../www/api/property.html#SetImageProperty">SetImageProperty()</a> methods. Here we set a property and fetch it right back:</p>
487 (void) SetImageProperty(image,"comment","This space for rent");
488 comment=GetImageProperty(image,"comment");
489 if (comment == (const char *) NULL)
490 (void) printf("Image comment: %s\n",comment);
493 <p>ImageMagick supports artifacts with the GetImageArtifact() and SetImageArtifact() methods. Artifacts are stealth properties that are not exported to image formats (e.g. PNG) and they do not display when identifying an image.</p>
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>
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);
512 <h2><a name="tera-pixel"></a>Large Image Support</h2>
513 <div class="doc-section">
514 <p>ImageMagick can read, process, or write mega-, giga-, or tera-pixel image sizes. An image width or height can range from 1 to 2 giga-pixels on a 32 bit OS and up to 9 exa-pixels on a 64-bit OS. Note, that some image formats have restrictions on image size. For example, Photoshop images are limited to 300,000 pixels for width or height. Here we resize an image to a quarter million pixels square:</p>
516 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert logo: -resize 250000x250000 logo.miff</span></p>
517 <p>For large images, ImageMagick will likely create a pixel cache on disk. Make sure you have plenty of temporary disk space. If your default temporary disk partition is too small, tell ImageMagick to use another partition with plenty of free space. For example:</p>
519 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp logo: \ <br/> -resize 250000x250000 logo.miff</span></p>
520 <p>To ensure large images do not consume all the memory on your system, force the image pixels to memory-mapped disk with resource limits:</p>
522 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit memory 16mb \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
523 <p>Here we force all image pixels to disk:</p>
525 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
526 <p>Caching pixels to disk is about 1000 times slower than memory. Expect long run times when processing large images on disk with ImageMagick. You can monitor progress with this command:</p>
528 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert -monitor -define registry:temporary-path=/data/tmp -limit area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p></div>
530 <h2><a name="threads"></a>Threads of Execution</h2>
531 <div class="doc-section">
533 <p>Many of ImageMagick's internal algorithms are threaded to take advantage of speed-ups offered by the multicore processor chips. However, you are welcome to use ImageMagick algorithms in your threads of execution with the exception of the MagickCore's GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), or SyncAuthenticPixels() pixel cache methods. These methods are intended for one thread of execution only. To access the pixel cache with more than one thread of execution, use a cache view. We do this for the <a href="../www/api/composite.html#CompositeImage">CompositeImage()</a> method, for example. Suppose we want to composite a single image over a different image in each thread of execution. If we use GetVirtualPixels(), the results are unpredictable because multiple threads would likely be asking for different areas of the pixel cache simultaneously. Instead we use GetCacheViewVirtualPixels() which creates a unique view for each thread of execution ensuring our program behaves properly regardless of how many threads are invoked. The other program interfaces, such as the <a href="../www/magick-wand.html">MagickWand API</a>, are completely thread safe so there are no special precautions for threads of execution.</p>
535 <p>Here is an example of how ImageMagick can take advantage of threads of execution with the <a href="http://en.wikipedia.org/wiki/OpenMP">OpenMP</a> programming paradigm:</p>
537 <div class="viewport">
550 image_view=AcquireCacheView(image);
551 #pragma omp parallel for schedule(dynamic,4) shared(status)
552 for (y=0; y < (long) image->rows; y++)
563 if (status == MagickFalse)
565 q=GetCacheViewAuthenticPixels(image_view,0,y,image->columns,1,exception);
566 if (q == (PixelPacket *) NULL)
571 indexes=GetCacheViewAuthenticIndexQueue(image_view);
572 for (x=0; x < (long) image->columns; x++)
578 if (indexes != (IndexPacket *) NULL)
582 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
585 image_view=DestroyCacheView(image_view);
586 if (status == MagickFalse)
587 perror("something went wrong");
593 <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>
595 <p><a href="../www/api/wand-view.html">MagickWand</a> support wand views. A view iterates over the entire, or portion, of the image in parallel and for each row of pixels, it invokes a callback method you provide. This limits most of your parallel programming activity to just that one module. There are similar methods in <a href="../www/api/image-view.html">MagickCore</a>. For an example, see the same sigmoidal contrast algorithm implemented in both <a href="../www/magick-wand.html#wand-view">MagickWand</a> and <a href="../www/magick-core.html#image-view">MagickCore</a>.</p>
597 <p>The OpenMP committee has not defined the behavior of mixing OpenMP with other threading models such as Posix threads. However, using modern releases of Linux, OpenMP and Posix threads appear to interoperate without complaint. If you want to use Posix threads from a program module that calls one of the ImageMagick application programming interfaces (e.g. MagickCore, MagickWand, Magick++, etc.) from Mac OS X or an older Linux release, you may need to disable OpenMP support within ImageMagick. Add the <kbd>--disable-openmp</kbd> option to the configure script command line and rebuild and reinstall ImageMagick.</p>
600 <h2><a name="distributed"></a>Heterogeneous Distributed Processing</h2>
601 <div class="doc-section">
602 <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>
604 <p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
606 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
607 <p>If so, run this command to realize a significant speed-up for image convolution:</p>
609 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.png convolve '-1, -1, -1, -1, 9, -1, -1, -1, -1' \ <br/> convolve.png</span></p>
610 <p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
612 <p>Here is an example OpenCL kernel that convolves an image:</p>
614 <div class="viewport">
616 static inline long ClampToCanvas(const long offset,const ulong range)
621 return((long) (range-1L));
625 static inline CLQuantum ClampToQuantum(const double value)
628 return((CLQuantum) 0);
629 if (value >= (double) QuantumRange)
630 return((CLQuantum) QuantumRange);
631 return((CLQuantum) (value+0.5));
634 __kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
635 const ulong width,const ulong height,__global CLPixelType *destination)
637 const ulong columns = get_global_size(0);
638 const ulong rows = get_global_size(1);
640 const long x = get_global_id(0);
641 const long y = get_global_id(1);
643 const double scale = (1.0/QuantumRange);
644 const long mid_width = (width-1)/2;
645 const long mid_height = (height-1)/2;
646 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
648 register ulong i = 0;
650 for (long v=(-mid_height); v <= mid_height; v++)
652 for (long u=(-mid_width); u <= mid_width; u++)
654 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,columns);
655 const double alpha=scale*(QuantumRange-source[index].w);
656 sum.x+=alpha*filter[i]*source[index].x;
657 sum.y+=alpha*filter[i]*source[index].y;
658 sum.z+=alpha*filter[i]*source[index].z;
659 sum.w+=filter[i]*source[index].w;
660 gamma+=alpha*filter[i];
665 gamma=1.0/(fabs(gamma) <= MagickEpsilon ? 1.0 : gamma);
666 const ulong index=y*columns+x;
667 destination[index].x=ClampToQuantum(gamma*sum.x);
668 destination[index].y=ClampToQuantum(gamma*sum.y);
669 destination[index].z=ClampToQuantum(gamma*sum.z);
670 destination[index].w=ClampToQuantum(sum.w);
675 <p>See <a href="http://trac.imagemagick.org/browser/ImageMagick/trunk/magick/accelerate.c">magick/accelerate.c</a> for a complete implementation of image convolution with an OpenCL kernel.</p>
679 <h2><a name="coders"></a>Custom Image Coders</h2>
680 <div class="doc-section">
682 <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>
684 <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>
686 <div class="viewport">
689 Include declarations.
691 #include "magick/studio.h"
692 #include "magick/blob.h"
693 #include "magick/blob-private.h"
694 #include "magick/colorspace.h"
695 #include "magick/exception.h"
696 #include "magick/exception-private.h"
697 #include "magick/image.h"
698 #include "magick/image-private.h"
699 #include "magick/list.h"
700 #include "magick/magick.h"
701 #include "magick/memory_.h"
702 #include "magick/monitor.h"
703 #include "magick/monitor-private.h"
704 #include "magick/quantum-private.h"
705 #include "magick/static.h"
706 #include "magick/string_.h"
707 #include "magick/module.h"
710 Forward declarations.
712 static MagickBooleanType
713 WriteMGKImage(const ImageInfo *,Image *);
716 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
724 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
726 % IsMGK() returns MagickTrue if the image format type, identified by the
727 % magick string, is MGK.
729 % The format of the IsMGK method is:
731 % MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
733 % A description of each parameter follows:
735 % o magick: This string is generally the first few bytes of an image file
738 % o length: Specifies the length of the magick string.
741 static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
745 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
751 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
755 % R e a d M G K I m a g e %
759 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
761 % ReadMGKImage() reads a MGK image file and returns it. It allocates
762 % the memory necessary for the new Image structure and returns a pointer to
765 % The format of the ReadMGKImage method is:
767 % Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
769 % A description of each parameter follows:
771 % o image_info: the image info.
773 % o exception: return any errors or warnings in this structure.
776 static Image *ReadMGKImage(const ImageInfo *image_info,
777 ExceptionInfo *exception)
780 buffer[MaxTextExtent];
797 register unsigned char
813 assert(image_info != (const ImageInfo *) NULL);
814 assert(image_info->signature == MagickSignature);
815 if (image_info->debug != MagickFalse)
816 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info->filename);
817 assert(exception != (ExceptionInfo *) NULL);
818 assert(exception->signature == MagickSignature);
819 image=AcquireImage(image_info);
820 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
821 if (status == MagickFalse)
823 image=DestroyImageList(image);
824 return((Image *) NULL);
829 (void) ReadBlobString(image,buffer); /* read magic number */
830 if (IsMGK(buffer,7) == MagickFalse)
831 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
832 (void) ReadBlobString(image,buffer);
833 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows);
835 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
839 Initialize image structure.
841 image->columns=columns;
844 if ((image_info->ping != MagickFalse) && (image_info->number_scenes != 0))
845 if (image->scene >= (image_info->scene+image_info->number_scenes-1))
848 Convert MGK raster image to pixel packets.
850 if (SetImageExtent(image,0,0) == MagickFalse)
852 InheritException(exception,&image->exception);
853 return(DestroyImageList(image));
855 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns,3UL*sizeof(*pixels));
856 if (pixels == (unsigned char *) NULL)
857 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
858 for (y=0; y < (long) image->rows; y++)
860 count=(ssize_t) ReadBlob(image,(size_t) (3*image->columns),pixels);
861 if (count != (ssize_t) (3*image->columns))
862 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
864 q=QueueAuthenticPixels(image,0,y,image->columns,1,exception);
865 if (q == (PixelPacket *) NULL)
867 for (x=0; x < (long) image->columns; x++)
869 q->red=ScaleCharToQuantum(*p++);
870 q->green=ScaleCharToQuantum(*p++);
871 q->blue=ScaleCharToQuantum(*p++);
874 if (SyncAuthenticPixels(image,exception) == MagickFalse)
876 if ((image->previous == (Image *) NULL) &&
877 (SetImageProgress(image,LoadImageTag,y,image>>rows) == MagickFalse))
880 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
881 if (EOFBlob(image) != MagickFalse)
883 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image->filename);
887 Proceed to next image.
889 if (image_info->number_scenes != 0)
890 if (image->scene >= (image_info->scene+image_info->number_scenes-1))
893 (void) ReadBlobString(image,buffer);
894 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows);
898 Allocate next image structure.
900 AcquireNextImage(image_info,image);
901 if (GetNextImageInList(image) == (Image *) NULL)
903 image=DestroyImageList(image);
904 return((Image *) NULL);
906 image=SyncNextImageInList(image);
907 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
908 if (status == MagickFalse)
911 } while (count != 0);
912 (void) CloseBlob(image);
913 return(GetFirstImageInList(image));
917 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
921 % R e g i s t e r M G K I m a g e %
925 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
927 % RegisterMGKImage() adds attributes for the MGK image format to
928 % the list of supported formats. The attributes include the image format
929 % tag, a method to read and/or write the format, whether the format
930 % supports the saving of more than one frame to the same file or blob,
931 % whether the format supports native in-memory I/O, and a brief
932 % description of the format.
934 % The format of the RegisterMGKImage method is:
936 % unsigned long RegisterMGKImage(void)
939 ModuleExport unsigned long RegisterMGKImage(void)
944 entry=SetMagickInfo("MGK");
945 entry->decoder=(DecodeImageHandler *) ReadMGKImage;
946 entry->encoder=(EncodeImageHandler *) WriteMGKImage;
947 entry->magick=(IsImageFormatHandler *) IsMGK;
948 entry->description=ConstantString("MGK");
949 entry->module=ConstantString("MGK");
950 (void) RegisterMagickInfo(entry);
951 return(MagickImageCoderSignature);
955 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
959 % U n r e g i s t e r M G K I m a g e %
963 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
965 % UnregisterMGKImage() removes format registrations made by the
966 % MGK module from the list of supported formats.
968 % The format of the UnregisterMGKImage method is:
970 % UnregisterMGKImage(void)
973 ModuleExport void UnregisterMGKImage(void)
975 (void) UnregisterMagickInfo("MGK");
979 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
983 % W r i t e M G K I m a g e %
987 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
989 % WriteMGKImage() writes an image to a file in red, green, and blue
990 % MGK rasterfile format.
992 % The format of the WriteMGKImage method is:
994 % MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
996 % A description of each parameter follows.
998 % o image_info: the image info.
1000 % o image: The image.
1003 static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1006 buffer[MaxTextExtent];
1017 register const PixelPacket
1023 register unsigned char
1030 Open output image file.
1032 assert(image_info != (const ImageInfo *) NULL);
1033 assert(image_info->signature == MagickSignature);
1034 assert(image != (Image *) NULL);
1035 assert(image->signature == MagickSignature);
1036 if (image->debug != MagickFalse)
1037 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
1038 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&image->exception);
1039 if (status == MagickFalse)
1045 Allocate memory for pixels.
1047 if (image->colorspace != RGBColorspace)
1048 (void) SetImageColorspace(image,RGBColorspace);
1049 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns,
1050 3UL*sizeof(*pixels));
1051 if (pixels == (unsigned char *) NULL)
1052 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1054 Initialize raster file header.
1056 (void) WriteBlobString(image,"id=mgk\n");
1057 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1058 image->columns,image->rows);
1059 (void) WriteBlobString(image,buffer);
1060 for (y=0; y < (long) image->rows; y++)
1062 p=GetVirtualPixels(image,0,y,image->columns,1,&image->exception);
1063 if (p == (const PixelPacket *) NULL)
1066 for (x=0; x < (long) image->columns; x++)
1068 *q++=ScaleQuantumToChar(p->red);
1069 *q++=ScaleQuantumToChar(p->green);
1070 *q++=ScaleQuantumToChar(p->blue);
1073 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
1074 if ((image->previous == (Image *) NULL) &&
1075 (SetImageProgress(image,SaveImageTag,y,image->rows) == MagickFalse))
1078 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1079 if (GetNextImageInList(image) == (Image *) NULL)
1081 image=SyncNextImageInList(image);
1082 status=SetImageProgress(image,SaveImagesTag,scene,
1083 GetImageListLength(image));
1084 if (status == MagickFalse)
1087 } while (image_info->adjoin != MagickFalse);
1088 (void) CloseBlob(image);
1094 <p>To invoke the custom coder from the command line, use these commands:</p>
1096 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert logo: logo.mgk</span><span class='crtout'></span><span class="crtprompt"> $magick> </span><span class='crtin'>display logo.mgk</span></p>
1097 <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>
1101 <h2><a name="filters"></a>Custom Image Filters</h2>
1102 <div class="doc-section">
1104 <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>
1106 <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>
1108 <div class="viewport">
1110 #include <stdio.h>
1111 #include <stdlib.h>
1112 #include <string.h>
1113 #include <time.h>
1114 #include <assert.h>
1115 #include <math.h>
1116 #include "magick/MagickCore.h"
1119 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1123 % a n a l y z e I m a g e %
1127 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1129 % analyzeImage() computes the brightness and saturation mean, standard
1130 % deviation, kurtosis and skewness and stores these values as attributes
1133 % The format of the analyzeImage method is:
1135 % unsigned long analyzeImage(Image *images,const int argc,
1136 % char **argv,ExceptionInfo *exception)
1138 % A description of each parameter follows:
1140 % o image: the address of a structure of type Image.
1142 % o argc: Specifies a pointer to an integer describing the number of
1143 % elements in the argument vector.
1145 % o argv: Specifies a pointer to a text array containing the command line
1148 % o exception: return any errors or warnings in this structure.
1151 ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1152 const char **argv,ExceptionInfo *exception)
1155 text[MaxTextExtent];
1161 brightness_standard_deviation,
1162 brightness_kurtosis,
1163 brightness_skewness,
1171 saturation_standard_deviation,
1172 saturation_kurtosis,
1173 saturation_skewness,
1182 assert(images != (Image **) NULL);
1183 assert(*images != (Image *) NULL);
1184 assert((*images)->signature == MagickSignature);
1188 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1199 brightness_sum_x=0.0;
1200 brightness_sum_x2=0.0;
1201 brightness_sum_x3=0.0;
1202 brightness_sum_x4=0.0;
1203 brightness_mean=0.0;
1204 brightness_standard_deviation=0.0;
1205 brightness_kurtosis=0.0;
1206 brightness_skewness=0.0;
1207 saturation_sum_x=0.0;
1208 saturation_sum_x2=0.0;
1209 saturation_sum_x3=0.0;
1210 saturation_sum_x4=0.0;
1211 saturation_mean=0.0;
1212 saturation_standard_deviation=0.0;
1213 saturation_kurtosis=0.0;
1214 saturation_skewness=0.0;
1217 image_view=AcquireCacheView(image);
1218 #if defined(MAGICKCORE_OPENMP_SUPPORT)
1219 #pragma omp parallel for schedule(dynamic,4) shared(status)
1221 for (y=0; y < (long) image->rows; y++)
1223 register const PixelPacket
1229 if (status == MagickFalse)
1231 p=GetCacheViewVirtualPixels(image_view,0,y,image->columns,1,exception);
1232 if (p == (const PixelPacket *) NULL)
1237 for (x=0; x < (long) image->columns; x++)
1239 ConvertRGBToHSB(p->red,p->green,p->blue,&hue,&saturation,&brightness);
1240 brightness*=QuantumRange;
1241 brightness_sum_x+=brightness;
1242 brightness_sum_x2+=brightness*brightness;
1243 brightness_sum_x3+=brightness*brightness*brightness;
1244 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1245 saturation*=QuantumRange;
1246 saturation_sum_x+=saturation;
1247 saturation_sum_x2+=saturation*saturation;
1248 saturation_sum_x3+=saturation*saturation*saturation;
1249 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1254 image_view=DestroyCacheView(image_view);
1257 brightness_mean=brightness_sum_x/area;
1258 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1259 (void) SetImageProperty(image,"filter:brightness:mean",text);
1260 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1261 area*brightness_sum_x/area));
1262 (void) FormatMagickString(text,MaxTextExtent,"%g",
1263 brightness_standard_deviation);
1264 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1265 if (brightness_standard_deviation != 0)
1266 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1267 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1268 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1269 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1270 brightness_standard_deviation*brightness_standard_deviation*
1271 brightness_standard_deviation)-3.0;
1272 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1273 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1274 if (brightness_standard_deviation != 0)
1275 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1276 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1277 brightness_mean)/(brightness_standard_deviation*
1278 brightness_standard_deviation*brightness_standard_deviation);
1279 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1280 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1281 saturation_mean=saturation_sum_x/area;
1282 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1283 (void) SetImageProperty(image,"filter:saturation:mean",text);
1284 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1285 area*saturation_sum_x/area));
1286 (void) FormatMagickString(text,MaxTextExtent,"%g",
1287 saturation_standard_deviation);
1288 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1289 if (saturation_standard_deviation != 0)
1290 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1291 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1292 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1293 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1294 saturation_standard_deviation*saturation_standard_deviation*
1295 saturation_standard_deviation)-3.0;
1296 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1297 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1298 if (saturation_standard_deviation != 0)
1299 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1300 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1301 saturation_mean)/(saturation_standard_deviation*
1302 saturation_standard_deviation*saturation_standard_deviation);
1303 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1304 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1306 return(MagickImageFilterSignature);
1311 <p>To invoke the custom filter from the command line, use this command:</p>
1313 <p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert logo: -process analyze -verbose info:</span><span class='crtout'>Image: logo: <br/>
1314 Format: LOGO (ImageMagick Logo) <br/>
1315 Class: PseudoClass <br/>
1316 Geometry: 640x480 <br/>
1318 filter:brightness:kurtosis: 8.98864 <br/>
1319 filter:brightness:mean: 238.096 <br/>
1320 filter:brightness:skewness: -3.04519 <br/>
1321 filter:brightness:standard-deviation: 46.3286 <br/>
1322 filter:saturation:kurtosis: 5.9137 <br/>
1323 filter:saturation:mean: 23.4635 <br/>
1324 filter:saturation:skewness: 2.71874 <br/>
1325 filter:saturation:standard-deviation: 64.7734</span></p>
1327 <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>
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