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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> 58 59 <h2 class="magick-header"><a id="overview"></a>Architecture Overview</h2> 60 61 <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> 62 63 <ul> 64 <li>colorspace (e.g sRGB, linear RGB, linear GRAY, CMYK, YUV, Lab, etc.)</li> 65 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li> 66 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li> 67 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li> 68 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li> 69 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li> 70 </ul> 71 72 <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> 73 74 <p>An efficient implementation of an image processing algorithm may require we get or set:</p> 75 76 <ul> 77 <li>one pixel a time (e.g. pixel at location 10,3)</li> 78 <li>a single scanline (e.g. all pixels from row 4)</li> 79 <li>a few scanlines at once (e.g. pixel rows 4-7)</li> 80 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li> 81 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li> 82 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li> 83 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li> 84 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li> 85 <li>a pixel component that is unsigned (65311) or in a floating-point representation (e.g. 0.17836)</li> 86 <li>a high-dynamic range pixel that can include negative values (e.g. -0.00716) as well as values that exceed the quantum depth (e.g. 65931)</li> 87 <li>one or more pixels simultaneously in different threads of execution</li> 88 <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> 89 </ul> 90 91 <p>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> 92 93 <p>Given the varied image formats and image processing requirements, we implemented the ImageMagick <a href="architecture.php#cache">pixel cache</a> to provide convenient sequential or parallel access to any pixel on demand anywhere inside the image region (i.e. <a href="architecture.php#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 (i.e. <a href="architecture.php#virtual-pixels">virtual pixels</a>).</p> 94 95 <p>In addition to pixels, images have a plethora of <a href="architecture.php#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> 96 97 <p>ImageMagick consists of nearly a half million 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, elegant, and efficient 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="architecture.php#threads">thread</a> of execution. In the final sections, we discuss <a href="architecture.php#coders">image coders</a> to read or write a particular image format followed by a few words on creating a <a href="architecture.php#filters">filter</a> to access or update pixels based on your custom requirements.</p> 98 99 <h2 class="magick-header"><a id="cache"></a>The Pixel Cache</h2> 100 101 <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="high-dynamic-range.php">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 only when you signal your intention to update any of the pixels.</p> 102 103 <h3>Create the Pixel Cache</h3> 104 105 <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> 106 107 <dl> 108 <dt>Create an image canvas initialized to the background color:</dt><br/> 109 <dd><pre>image=AllocateImage(image_info); 110 if (SetImageExtent(image,640,480) == MagickFalse) 111 { /* an exception was thrown */ } 112 (void) QueryMagickColor("red",&image->background_color,&image->exception); 113 SetImageBackgroundColor(image); 114 </pre></dd> 115 116 <dt>Create an image from a JPEG image on disk:</dt><br/> 117 <dd><pre>(void) strcpy(image_info->filename,"image.jpg"): 118 image=ReadImage(image_info,exception); 119 if (image == (Image *) NULL) 120 { /* an exception was thrown */ } 121 </pre></dd> 122 <dt>Create an image from a memory based image:</dt><br/> 123 <dd><pre>image=BlobToImage(blob_info,blob,extent,exception); 124 if (image == (Image *) NULL) 125 { /* an exception was thrown */ } 126 </pre></dd> 127 </dl> 128 129 <p>In our discussion of the pixel cache, we use the <a href="magick-core.php">MagickCore API</a> to illustrate our points, however, the principles are the same for other program interfaces to ImageMagick.</p> 130 131 <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="command-line-options.php#version">‑version</a> option: </p> 132 133 <pre><span class="crtprompt"> </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 7.0.0-0 2015-12-10 Q16 http://www.imagemagick.org</span></pre> 134 <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> 135 136 <h3><a id="authentic-pixels"></a>Access the Pixel Cache</h3> 137 138 <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 <a href="architecture.php#authentic-pixels">authentic pixels</a> and outside the region as <a href="architecture.php#virtual-pixels">virtual pixels</a>. Use these methods to access the pixels in the cache:</p> 139 <ul> 140 <li><a href="../api/cache.php#GetVirtualPixels">GetVirtualPixels()</a>: gets pixels that you do not intend to modify or pixels that lie outside the image region (e.g. pixel @ -1,-3)</li> 141 <li><a href="../api/cache.php#GetAuthenticPixels">GetAuthenticPixels()</a>: gets pixels that you intend to modify</li> 142 <li><a href="../api/cache.php#QueueAuthenticPixels">QueueAuthenticPixels()</a>: queue pixels that you intend to set</li> 143 <li><a href="../api/cache.php#SyncAuthenticPixels">SyncAuthenticPixels()</a>: update the pixel cache with any modified pixels</li> 144 </ul> 145 146 <p>Here is a typical <a href="magick-core.php">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> 147 148 <pre class="pre-scrollable">const PixelPacket 149 *p; 150 151 PixelPacket 152 *q; 153 154 ssize_t 155 x, 156 y; 157 158 destination=CloneImage(source,source->columns,source->rows,MagickTrue, 159 exception); 160 if (destination == (Image *) NULL) 161 { /* an exception was thrown */ } 162 for (y=0; y < (ssize_t) source->rows; y++) 163 { 164 p=GetVirtualPixels(source,0,y,source->columns,1,exception); 165 q=GetAuthenticPixels(destination,0,y,destination->columns,1,exception); 166 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL) 167 break; 168 for (x=0; x < (ssize_t) source->columns; x++) 169 { 170 SetPixelRed(q,90*p->red/100); 171 SetPixelGreen(q,90*p->green/100); 172 SetPixelBlue(q,90*p->blue/100); 173 SetPixelOpacity(q,90*p->opacity/100); 174 p++; 175 q++; 176 } 177 if (SyncAuthenticPixels(destination,exception) == MagickFalse) 178 break; 179 } 180 if (y < (ssize_t) source->rows) 181 { /* an exception was thrown */ } 182 </pre> 183 184 <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 or set the pixel cache by calling <a href="../api/cache.php#GetAuthenticPixels">GetAuthenticPixels()</a> or <a href="../api/cache.php#QueueAuthenticPixels">QueueAuthenticPixels()</a>. Use <a href="../api/cache.php#QueueAuthenticPixels">QueueAuthenticPixels()</a> if you want to set new pixel values rather than update existing ones. You could use GetAuthenticPixels() to set pixel values but it is slightly more efficient to use QueueAuthenticPixels() instead. Finally, use <a href="../api/cache.php#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p> 185 186 <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="../api/cache.php#GetVirtualIndexQueue">GetVirtualIndexQueue()</a> (to read the indexes) or <a href="../api/cache.php#GetAuthenticIndexQueue">GetAuthenticIndexQueue()</a> (to update the indexes) to gain access to this channel. For example, to print the colormap indexes, use:</p> 187 188 <pre>const IndexPacket 189 *indexes; 190 191 for (y=0; y < (ssize_t) source->rows; y++) 192 { 193 p=GetVirtualPixels(source,0,y,source->columns,1); 194 if (p == (const PixelPacket *) NULL) 195 break; 196 indexes=GetVirtualIndexQueue(source); 197 for (x=0; x < (ssize_t) source->columns; x++) 198 (void) printf("%d\n",GetPixelIndex(indexes+x)); 199 } 200 if (y < (ssize_t) source->rows) 201 /* an exception was thrown */ 202 </pre> 203 204 <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 <var>pushed</var> 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> 205 206 <pre>p=GetVirtualPixels(source,-3,-3,source->columns+3,6,exception); 207 </pre> 208 209 <p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p> 210 211 <h3><a id="virtual-pixels"></a>Virtual Pixels</h3> 212 213 <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> 214 <p>Access to the virtual pixels are controlled by the <a href="../api/cache.php#SetImageVirtualPixelMethod">SetImageVirtualPixelMethod()</a> method from the MagickCore API or the <a href="command-line-options.php#virtual-pixel">‑virtual‑pixel</a> option from the command line. The methods include:</p> 215 216 <dl class="dl-horizontal"> 217 <dt>background</dt> 218 <dd>the area surrounding the image is the background color</dd> 219 <dt>black</dt> 220 <dd>the area surrounding the image is black</dd> 221 <dt>checker-tile</dt> 222 <dd>alternate squares with image and background color</dd> 223 <dt>dither</dt> 224 <dd>non-random 32x32 dithered pattern</dd> 225 <dt>edge</dt> 226 <dd>extend the edge pixel toward infinity (default)</dd> 227 <dt>gray</dt> 228 <dd>the area surrounding the image is gray</dd> 229 <dt>horizontal-tile</dt> 230 <dd>horizontally tile the image, background color above/below</dd> 231 <dt>horizontal-tile-edge</dt> 232 <dd>horizontally tile the image and replicate the side edge pixels</dd> 233 <dt>mirror</dt> 234 <dd>mirror tile the image</dd> 235 <dt>random</dt> 236 <dd>choose a random pixel from the image</dd> 237 <dt>tile</dt> 238 <dd>tile the image</dd> 239 <dt>transparent</dt> 240 <dd>the area surrounding the image is transparent blackness</dd> 241 <dt>vertical-tile</dt> 242 <dd>vertically tile the image, sides are background color</dd> 243 <dt>vertical-tile-edge</dt> 244 <dd>vertically tile the image and replicate the side edge pixels</dd> 245 <dt>white</dt> 246 <dd>the area surrounding the image is white</dd> 247 </dl> 248 249 250 <h3>Cache Storage and Resource Requirements</h3> 251 252 <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 <var>width * height * bit-depth / 8 * channels</var> 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 <var>automagically</var> by the pixel cache manager negotiating with the operating system. However, you can influence how the pixel cache manager allocates the pixel cache with <var>cache resource limits</var>. The limits include:</p> 253 254 <dl class="dl-horizontal"> 255 <dt>width</dt> 256 <dd>maximum width of an image. Exceed this limit and an exception is thrown and processing stops.</dd> 257 <dt>height</dt> 258 <dd>maximum height of an image. Exceed this limit and an exception is thrown and processing stops.</dd> 259 <dt>area</dt> 260 <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 and optionally memory-mapped.</dd> 261 <dt>memory</dt> 262 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd> 263 <dt>map</dt> 264 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd> 265 <dt>disk</dt> 266 <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> 267 <dt>files</dt> 268 <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 without a speed penalty due to repeated open/close calls.</dd> 269 <dt>thread</dt> 270 <dd>maximum number of threads that are permitted to run in parallel.</dd> 271 <dt>time</dt> 272 <dd>maximum number of seconds that the process is permitted to execute. Exceed this limit and an exception is thrown and processing stops.</dd> 273 </dl> 274 275 <p>To determine the current setting of these limits, use this command:</p> 276 277 <pre> 278 -> identify -list resource 279 Resource limits: 280 Width: 100MP 281 Height: 100MP 282 Area: 25.181GB 283 Memory: 11.726GiB 284 Map: 23.452GiB 285 Disk: unlimited 286 File: 768 287 Thread: 12 288 Throttle: 0 289 Time: unlimited 290 </pre> 291 292 <p>You can set these limits either as a <a href="resources.php#configure">policy</a> (see <a href="../source/policy.xml">policy.xml</a>), with an <a href="resources.php#environment">environment variable</a>, with the <a href="command-line-options.php#limit">-limit</a> command line option, or with the <a href="../api/resource.php#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>, includes these policy limits to help prevent a denial-of-service:</p> 293 <pre> 294 <policymap> 295 <policy domain="resource" name="temporary-path" value="/tmp"/> 296 <policy domain="resource" name="memory" value="256MiB"/> 297 <policy domain="resource" name="map" value="512MiB"/> 298 <policy domain="resource" name="width" value="8KP"/> 299 <policy domain="resource" name="height" value="8KP"/> 300 <policy domain="resource" name="area" value="128MB"/> 301 <policy domain="resource" name="disk" value="1GiB"/> 302 <policy domain="resource" name="file" value="768"/> 303 <policy domain="resource" name="thread" value="2"/> 304 <policy domain="resource" name="throttle" value="0"/> 305 <policy domain="resource" name="time" value="120"/> 306 <policy domain="system" name="precision" value="6"/> 307 <policy domain="cache" name="shared-secret" value="replace with your secret phrase"/> 308 </policymap> 309 </pre> 310 <p>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 time limit to prevent any run-away processing tasks.</p> 311 312 <p>Note, the cache limits are global to each invocation of ImageMagick, meaning if you create several images, the combined resource requirements are compared to the limit to determine the pixel cache storage disposition.</p> 313 314 <p>To determine which type and how much resources are consumed by the pixel cache, add the <a href="command-line-options.php#debug">-debug cache</a> option to the command-line:</p> 315 <pre>-> convert -debug cache logo: -sharpen 3x2 null: 316 2013-12-17T13:33:42-05:00 0:00.000 0.000u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 317 destroy 318 2013-12-17T13:33:42-05:00 0:00.000 0.000u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 319 open LOGO[0] (Heap Memory, 640x480x4 4.688MiB) 320 2013-12-17T13:33:42-05:00 0:00.010 0.000u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 321 open LOGO[0] (Heap Memory, 640x480x3 3.516MiB) 322 2013-12-17T13:33:42-05:00 0:00.010 0.000u 7.0.0 Cache convert: cache.c/ClonePixelCachePixels/1044/Cache 323 Memory => Memory 324 2013-12-17T13:33:42-05:00 0:00.020 0.010u 7.0.0 Cache convert: cache.c/ClonePixelCachePixels/1044/Cache 325 Memory => Memory 326 2013-12-17T13:33:42-05:00 0:00.020 0.010u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 327 open LOGO[0] (Heap Memory, 640x480x3 3.516MiB) 328 2013-12-17T13:33:42-05:00 0:00.050 0.100u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 329 destroy LOGO[0] 330 2013-12-17T13:33:42-05:00 0:00.050 0.100u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 331 destroy LOGO[0] 332 </pre> 333 <p>This command utilizes a pixel cache in memory. The logo consumed 4.688MiB and after it was sharpened, 3.516MiB.</p> 334 335 336 <h3>Distributed Pixel Cache</h3> 337 <p>A distributed pixel cache is an extension of the traditional pixel cache available on a single host. The distributed pixel cache may span multiple servers so that it can grow in size and transactional capacity to support very large images. Start up the pixel cache server on one or more machines. When you read or operate on an image and the local pixel cache resources are exhausted, ImageMagick contacts one or more of these remote pixel servers to store or retrieve pixels. The distributed pixel cache relies on network bandwidth to marshal pixels to and from the remote server. As such, it will likely be significantly slower than a pixel cache utilizing local storage (e.g. memory, disk, etc.).</p> 338 339 <h3>Cache Views</h3> 340 341 <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 <var>cache view</var>. A cache view permits you to access as many areas simultaneously in the pixel cache as you require. The cache view <a href="../api/cache-view.php">methods</a> are analogous to 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 the first and last pixel row of the image simultaneously:</p> 342 343 <pre class="pre-scrollable">CacheView 344 *view_1, 345 *view_2; 346 347 view_1=AcquireVirtualCacheView(source,exception); 348 view_2=AcquireVirtualCacheView(source,exception); 349 for (y=0; y < (ssize_t) source->rows; y++) 350 { 351 u=GetCacheViewVirtualPixels(view_1,0,y,source->columns,1,exception); 352 v=GetCacheViewVirtualPixels(view_2,0,source->rows-y-1,source->columns,1,exception); 353 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL)) 354 break; 355 for (x=0; x < (ssize_t) source->columns; x++) 356 { 357 /* do something with u & v here */ 358 } 359 } 360 view_2=DestroyCacheView(view_2); 361 view_1=DestroyCacheView(view_1); 362 if (y < (ssize_t) source->rows) 363 { /* an exception was thrown */ } 364 </pre> 365 366 <h3>Magick Persistent Cache Format</h3> 367 368 <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 <code>.mpc</code>, retains all the properties associated with the image or image sequence (e.g. width, height, colorspace, etc.) and the second, with the extension <code>.cache</code>, 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> 369 <p>The most efficient use of MPC image files is a write-once, read-many-times pattern. For example, your workflow requires extracting random blocks of pixels from the source image. Rather than re-reading and possibly decompressing the source image each time, we use MPC and map the image directly to memory.</p> 370 371 <h3>Best Practices</h3> 372 373 <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. Although you can access scanlines of pixels sequentially from the last row of the image to the first, you may get a performance boost if you access scanlines from the first row of the image to the last, in sequential order.</p> 374 375 <p>You can get, modify, or set pixels in row or column order. However, it is more efficient to access the pixels by row rather than by column.</p> 376 377 <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> 378 379 <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 any pixel changes to the pixel cache.</p> 380 381 <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="architecture.php#threads">thread of execution</a> is accessing the image.</p> 382 383 <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> 384 385 <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> 386 387 <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 many 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> 388 389 <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="high-dynamic-range.php">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 may have unexpected results due to out-of-band pixel values than the non-HDRI version.</p> 390 391 <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 <code>/tmp</code> and for Windows, <code>c:/temp</code>. You can tell ImageMagick to write the pixel cache to an alternate location and conserve memory with these options:</p> 392 393 <pre> 394 convert -limit memory 2GB -limit map 4GB -define registry:temporary-path=/data/tmp ... 395 </pre> 396 397 <p>Set global resource limits for your environment in the <code>policy.xml</code> configuration file.</p> 398 399 <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> 400 401 <pre> 402 convert image.tif image.mpc 403 convert image.mpc -crop 100x100+0+0 +repage 1.png 404 convert image.mpc -crop 100x100+100+0 +repage 2.png 405 convert image.mpc -crop 100x100+200+0 +repage 3.png 406 </pre> 407 408 <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> 409 410 <h2 class="magick-header"><a id="stream"></a>Streaming Pixels</h2> 411 412 <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> 413 414 <p>Use <a href="../api/stream.php#ReadStream">ReadStream()</a> or <a href="../api/stream.php#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> 415 416 <pre class="pre-scrollable">static size_t StreamPixels(const Image *image,const void *pixels,const size_t columns) 417 { 418 register const PixelPacket 419 *p; 420 421 MyData 422 *my_data; 423 424 my_data=(MyData *) image->client_data; 425 p=(PixelPacket *) pixels; 426 if (p != (const PixelPacket *) NULL) 427 { 428 /* process pixels here */ 429 } 430 return(columns); 431 } 432 433 ... 434 435 /* invoke the pixel stream here */ 436 image_info->client_data=(void *) MyData; 437 image=ReadStream(image_info,&StreamPixels,exception); 438 </pre> 439 440 <p>We also provide a lightweight tool, <a href="stream.php">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 href="stream.php">stream</a> desirable when working with large images or when you require raw pixel components. A majority of the image formats stream pixels (red, green, and blue) from left to right and top to bottom. However, a few formats do not support this common ordering (e.g. the PSD format).</p> 441 442 <h2 class="magick-header"><a id="properties"></a>Image Properties and Profiles</h2> 443 444 <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> 445 446 <pre>(void) printf("image width: %lu, height: %lu\n",image->columns,image->rows); 447 </pre> 448 449 <p>For a great majority of image properties, such as an image comment or description, we use the <a href="../api/property.php#GetImageProperty">GetImageProperty()</a> and <a href="../api/property.php#SetImageProperty">SetImageProperty()</a> methods. Here we set a property and fetch it right back:</p> 450 451 <pre>const char 452 *comment; 453 454 (void) SetImageProperty(image,"comment","This space for rent"); 455 comment=GetImageProperty(image,"comment"); 456 if (comment == (const char *) NULL) 457 (void) printf("Image comment: %s\n",comment); 458 </pre> 459 460 <p>ImageMagick supports artifacts with the GetImageArtifact() and SetImageArtifact() methods. Artifacts are stealth properties that are not exported to image formats (e.g. PNG).</p> 461 462 <p>Image profiles are handled with <a href="../api/profile.php#GetImageProfile">GetImageProfile()</a>, <a href="../api/profile.php#SetImageProfile">SetImageProfile()</a>, and <a href="../api/profile.php#ProfileImage">ProfileImage()</a> methods. Here we set a profile and fetch it right back:</p> 463 464 <pre>StringInfo 465 *profile; 466 467 profile=AcquireStringInfo(length); 468 SetStringInfoDatum(profile,my_exif_profile); 469 (void) SetImageProfile(image,"EXIF",profile); 470 DestroyStringInfo(profile); 471 profile=GetImageProfile(image,"EXIF"); 472 if (profile != (StringInfo *) NULL) 473 (void) PrintStringInfo(stdout,"EXIF",profile); 474 </pre> 475 476 <h2 class="magick-header"><a id="tera-pixel"></a>Large Image Support</h2> 477 <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> 478 479 <pre> 480 convert logo: -resize 250000x250000 logo.miff 481 </pre> 482 483 <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> 484 485 <pre> 486 convert -define registry:temporary-path=/data/tmp logo: \ <br/> -resize 250000x250000 logo.miff 487 </pre> 488 489 <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> 490 491 <pre> 492 convert -define registry:temporary-path=/data/tmp -limit memory 16mb \ 493 logo: -resize 250000x250000 logo.miff 494 </pre> 495 496 <p>Here we force all image pixels to disk:</p> 497 498 <pre> 499 convert -define registry:temporary-path=/data/tmp -limit area 0 \ 500 logo: -resize 250000x250000 logo.miff 501 </pre> 502 503 <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> 504 505 <pre>convert -monitor -limit memory 2GiB -limit map 4GiB -define registry:temporary-path=/data/tmp \ 506 logo: -resize 250000x250000 logo.miff 507 </pre> 508 509 <p>For really large images, or if there is limited resources on your host, you can utilize a distributed pixel cache on one or more remote hosts:</p> 510 <pre> 511 convert -distribute-cache 6668 & // start on 192.168.100.50 512 convert -distribute-cache 6668 & // start on 192.168.100.51 513 convert -limit memory 2mb -limit map 2mb -limit disk 2gb \ 514 -define registry:cache:hosts=192.168.100.50:6668,192.168.100.51:6668 \ 515 myhugeimage.jpg -sharpen 5x2 myhugeimage.png 516 </pre> 517 518 <h2 class="magick-header"><a id="threads"></a>Threads of Execution</h2> 519 520 <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 with the exception of an OpenMP parallel section. To access the pixel cache with more than one thread of execution, use a cache view. We do this for the <a href="../api/composite.php#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="magick-wand.php">MagickWand API</a>, are completely thread safe so there are no special precautions for threads of execution.</p> 521 522 <p>Here is an MagickCore code snippet that takes advantage of threads of execution with the <a href="openmp.php">OpenMP</a> programming paradigm:</p> 523 524 <pre class="pre-scrollable">CacheView 525 *image_view; 526 527 MagickBooleanType 528 status; 529 530 ssize_t 531 y; 532 533 status=MagickTrue; 534 image_view=AcquireVirtualCacheView(image,exception); 535 #pragma omp parallel for schedule(dynamic,4) shared(status) 536 for (y=0; y < (ssize_t) image->rows; y++) 537 { 538 register IndexPacket 539 *indexes; 540 541 register PixelPacket 542 *q; 543 544 register ssize_t 545 x; 546 547 if (status == MagickFalse) 548 continue; 549 q=GetCacheViewAuthenticPixels(image_view,0,y,image->columns,1,exception); 550 if (q == (PixelPacket *) NULL) 551 { 552 status=MagickFalse; 553 continue; 554 } 555 indexes=GetCacheViewAuthenticIndexQueue(image_view); 556 for (x=0; x < (ssize_t) image->columns; x++) 557 { 558 SetPixelRed(q,...); 559 SetPixelGreen(q,...); 560 SetPixelBlue(q,...); 561 SetPixelOpacity(q,...); 562 if (indexes != (IndexPacket *) NULL) 563 SetPixelIndex(indexes+x,...); 564 q++; 565 } 566 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse) 567 status=MagickFalse; 568 } 569 image_view=DestroyCacheView(image_view); 570 if (status == MagickFalse) 571 perror("something went wrong"); 572 </pre> 573 574 <p>This code snippet converts an uncompressed Windows bitmap to a Magick++ image:</p> 575 576 <pre class="pre-scrollable">#include "Magick++.h" 577 #include <assert.h> 578 #include "omp.h" 579 580 void ConvertBMPToImage(const BITMAPINFOHEADER *bmp_info, 581 const unsigned char *restrict pixels,Magick::Image *image) 582 { 583 /* 584 Prepare the image so that we can modify the pixels directly. 585 */ 586 assert(bmp_info->biCompression == BI_RGB); 587 assert(bmp_info->biWidth == image->columns()); 588 assert(abs(bmp_info->biHeight) == image->rows()); 589 image->modifyImage(); 590 if (bmp_info->biBitCount == 24) 591 image->type(MagickCore::TrueColorType); 592 else 593 image->type(MagickCore::TrueColorMatteType); 594 register unsigned int bytes_per_row=bmp_info->biWidth*bmp_info->biBitCount/8; 595 if (bytes_per_row % 4 != 0) { 596 bytes_per_row=bytes_per_row+(4-bytes_per_row % 4); // divisible by 4. 597 } 598 /* 599 Copy all pixel data, row by row. 600 */ 601 #pragma omp parallel for 602 for (int y=0; y < int(image->rows()); y++) 603 { 604 int 605 row; 606 607 register const unsigned char 608 *restrict p; 609 610 register MagickCore::PixelPacket 611 *restrict q; 612 613 row=(bmp_info->biHeight > 0) ? (image->rows()-y-1) : y; 614 p=pixels+row*bytes_per_row; 615 q=image->setPixels(0,y,image->columns(),1); 616 for (int x=0; x < int(image->columns()); x++) 617 { 618 SetPixelBlue(q,p[0]); 619 SetPixelGreen(q,p[1]); 620 SetPixelRed(q,p[2]); 621 if (bmp_info->biBitCount == 32) { 622 SetPixelOpacity(q,p[3]); 623 } 624 q++; 625 p+=bmp_info->biBitCount/8; 626 } 627 image->syncPixels(); // sync pixels to pixel cache. 628 } 629 return; 630 }</pre> 631 632 <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 <var>before</var> you call the API otherwise ImageMagick may fault.</p> 633 634 <p><a href="../api/wand-view.php">MagickWand</a> supports 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="../api/image-view.php">MagickCore</a>. For an example, see the same sigmoidal contrast algorithm implemented in both <a href="magick-wand.php#wand-view">MagickWand</a> and <a href="magick-core.php#image-view">MagickCore</a>.</p> 635 636 <p>In most circumstances, the default number of threads is set to the number of processor cores on your system for optimal performance. However, if your system is hyperthreaded or if you are running on a virtual host and only a subset of the processors are available to your server instance, you might get an increase in performance by setting the thread <a href="resources.php#configure">policy</a> or the <a href="resources.php#environment">MAGICK_THREAD_LIMIT</a> environment variable. For example, your virtual host has 8 processors but only 2 are assigned to your server instance. The default of 8 threads can cause severe performance problems. One solution is to limit the number of threads to the available processors in your <a href="../source/policy.xml">policy.xml</a> configuration file:</p> 637 638 <pre> 639 <policy domain="resource" name="thread" value="2"/> 640 </pre> 641 642 <p>Or suppose your 12 core hyperthreaded computer defaults to 24 threads. Set the MAGICK_THREAD_LIMIT environment variable and you will likely get improved performance:</p> 643 644 <pre> 645 export MAGICK_THREAD_LIMIT=12 646 </pre> 647 648 <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 <code>--disable-openmp</code> option to the configure script command line and rebuild and reinstall ImageMagick.</p> 649 650 <h4>Threading Performance</h4> 651 <p>It can be difficult to predict behavior in a parallel environment. Performance might depend on a number of factors including the compiler, the version of the OpenMP library, the processor type, the number of cores, the amount of memory, whether hyperthreading is enabled, the mix of applications that are executing concurrently with ImageMagick, or the particular image-processing algorithm you utilize. The only way to be certain of optimal performance, in terms of the number of threads, is to benchmark. ImageMagick includes progressive threading when benchmarking a command and returns the elapsed time and efficiency for one or more threads. This can help you identify how many threads is the most efficient in your environment. For this benchmark we sharpen a 1920x1080 image of a model 10 times with 1 to 12 threads:</p> 652 <pre> 653 convert -bench 10 model.png -sharpen 5x2 null: 654 Performance[1]: 10i 1.135ips 1.000e 8.760u 0:08.810 655 Performance[2]: 10i 2.020ips 0.640e 9.190u 0:04.950 656 Performance[3]: 10i 2.786ips 0.710e 9.400u 0:03.590 657 Performance[4]: 10i 3.378ips 0.749e 9.580u 0:02.960 658 Performance[5]: 10i 4.032ips 0.780e 9.580u 0:02.480 659 Performance[6]: 10i 4.566ips 0.801e 9.640u 0:02.190 660 Performance[7]: 10i 3.788ips 0.769e 10.980u 0:02.640 661 Performance[8]: 10i 4.115ips 0.784e 12.030u 0:02.430 662 Performance[9]: 10i 4.484ips 0.798e 12.860u 0:02.230 663 Performance[10]: 10i 4.274ips 0.790e 14.830u 0:02.340 664 Performance[11]: 10i 4.348ips 0.793e 16.500u 0:02.300 665 Performance[12]: 10i 4.525ips 0.799e 18.320u 0:02.210 666 </pre> 667 <p>The sweet spot for this example is 6 threads. This makes sense since there are 6 physical cores. The other 6 are hyperthreads. It appears that sharpening does not benefit from hyperthreading.</p> 668 <p>In certain cases, it might be optimal to set the number of threads to 1 or to disable OpenMP completely with the <a href="resources.php#environment">MAGICK_THREAD_LIMIT</a> environment variable, <a href="command-line-options.php#limit">-limit</a> command line option, or the <a href="resources.php#configure">policy.xml</a> configuration file.</p> 669 670 <h2 class="magick-header"><a id="distributed"></a>Heterogeneous Distributed Processing</h2> 671 <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> 672 673 <p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p> 674 675 <pre> 676 identify -version 677 Features: DPC Cipher Modules OpenCL OpenMP 678 </pre> 679 680 <p>If so, run this command to realize a significant speed-up for image convolution:</p> 681 682 <pre> 683 convert image.png -convolve '-1, -1, -1, -1, 9, -1, -1, -1, -1' convolve.png 684 </pre> 685 686 <p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p> 687 688 <p>Here is an example OpenCL kernel that convolves an image:</p> 689 690 <pre class="pre-scrollable">static inline long ClampToCanvas(const long offset,const ulong range) 691 { 692 if (offset < 0L) 693 return(0L); 694 if (offset >= range) 695 return((long) (range-1L)); 696 return(offset); 697 } 698 699 static inline CLQuantum ClampToQuantum(const float value) 700 { 701 if (value < 0.0) 702 return((CLQuantum) 0); 703 if (value >= (float) QuantumRange) 704 return((CLQuantum) QuantumRange); 705 return((CLQuantum) (value+0.5)); 706 } 707 708 __kernel void Convolve(const __global CLPixelType *source,__constant float *filter, 709 const ulong width,const ulong height,__global CLPixelType *destination) 710 { 711 const ulong columns = get_global_size(0); 712 const ulong rows = get_global_size(1); 713 714 const long x = get_global_id(0); 715 const long y = get_global_id(1); 716 717 const float scale = (1.0/QuantumRange); 718 const long mid_width = (width-1)/2; 719 const long mid_height = (height-1)/2; 720 float4 sum = { 0.0, 0.0, 0.0, 0.0 }; 721 float gamma = 0.0; 722 register ulong i = 0; 723 724 for (long v=(-mid_height); v <= mid_height; v++) 725 { 726 for (long u=(-mid_width); u <= mid_width; u++) 727 { 728 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u, 729 columns); 730 const float alpha=scale*(QuantumRange-source[index].w); 731 sum.x+=alpha*filter[i]*source[index].x; 732 sum.y+=alpha*filter[i]*source[index].y; 733 sum.z+=alpha*filter[i]*source[index].z; 734 sum.w+=filter[i]*source[index].w; 735 gamma+=alpha*filter[i]; 736 i++; 737 } 738 } 739 740 gamma=1.0/(fabs(gamma) <= MagickEpsilon ? 1.0 : gamma); 741 const ulong index=y*columns+x; 742 destination[index].x=ClampToQuantum(gamma*sum.x); 743 destination[index].y=ClampToQuantum(gamma*sum.y); 744 destination[index].z=ClampToQuantum(gamma*sum.z); 745 destination[index].w=ClampToQuantum(sum.w); 746 };</pre> 747 748 <p>See <a href="https://github.com/ImageMagick/ImageMagick/tree/ImageMagick-6/magick/accelerate.c">magick/accelerate.c</a> for a complete implementation of image convolution with an OpenCL kernel.</p> 749 750 <p>Note, that under Windows, you might have an issue with TDR (Timeout Detection and Recovery of GPUs). Its purpose is to detect runaway tasks hanging the GPU by using an execution time threshold. For some older low-end GPUs running the OpenCL filters in ImageMagick, longer execution times might trigger the TDR mechanism and pre-empt the GPU image filter. When this happens, ImageMagick automatically falls back to the CPU code path and returns the expected results. To avoid pre-emption, increase the <a href="http://msdn.microsoft.com/en-us/library/windows/hardware/gg487368.aspx">TdrDelay</a> registry key.</p> 751 752 <h2 class="magick-header"><a id="coders"></a>Custom Image Coders</h2> 753 754 <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> 755 756 <p>Here is a listing of a sample <a href="../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> 757 758 <pre class="pre-scrollable">/* 759 Include declarations. 760 */ 761 #include "magick/studio.h" 762 #include "magick/blob.h" 763 #include "magick/blob-private.h" 764 #include "magick/colorspace.h" 765 #include "magick/exception.h" 766 #include "magick/exception-private.h" 767 #include "magick/image.h" 768 #include "magick/image-private.h" 769 #include "magick/list.h" 770 #include "magick/magick.h" 771 #include "magick/memory_.h" 772 #include "magick/monitor.h" 773 #include "magick/monitor-private.h" 774 #include "magick/quantum-private.h" 775 #include "magick/static.h" 776 #include "magick/string_.h" 777 #include "magick/module.h" 778 779 /* 780 Forward declarations. 781 */ 782 static MagickBooleanType 783 WriteMGKImage(const ImageInfo *,Image *); 784 785 /* 786 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 787 % % 788 % % 789 % % 790 % I s M G K % 791 % % 792 % % 793 % % 794 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 795 % 796 % IsMGK() returns MagickTrue if the image format type, identified by the 797 % magick string, is MGK. 798 % 799 % The format of the IsMGK method is: 800 % 801 % MagickBooleanType IsMGK(const unsigned char *magick,const size_t length) 802 % 803 % A description of each parameter follows: 804 % 805 % o magick: This string is generally the first few bytes of an image file 806 % or blob. 807 % 808 % o length: Specifies the length of the magick string. 809 % 810 */ 811 static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length) 812 { 813 if (length < 7) 814 return(MagickFalse); 815 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0) 816 return(MagickTrue); 817 return(MagickFalse); 818 } 819 820 /* 821 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 822 % % 823 % % 824 % % 825 % R e a d M G K I m a g e % 826 % % 827 % % 828 % % 829 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 830 % 831 % ReadMGKImage() reads a MGK image file and returns it. It allocates 832 % the memory necessary for the new Image structure and returns a pointer to 833 % the new image. 834 % 835 % The format of the ReadMGKImage method is: 836 % 837 % Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception) 838 % 839 % A description of each parameter follows: 840 % 841 % o image_info: the image info. 842 % 843 % o exception: return any errors or warnings in this structure. 844 % 845 */ 846 static Image *ReadMGKImage(const ImageInfo *image_info, 847 ExceptionInfo *exception) 848 { 849 char 850 buffer[MaxTextExtent]; 851 852 Image 853 *image; 854 855 MagickBooleanType 856 status; 857 858 register PixelPacket 859 *q; 860 861 register size_t 862 x; 863 864 register unsigned char 865 *p; 866 867 ssize_t 868 count, 869 y; 870 871 unsigned char 872 *pixels; 873 874 unsigned long 875 columns, 876 rows; 877 878 /* 879 Open image file. 880 */ 881 assert(image_info != (const ImageInfo *) NULL); 882 assert(image_info->signature == MagickSignature); 883 if (image_info->debug != MagickFalse) 884 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info->filename); 885 assert(exception != (ExceptionInfo *) NULL); 886 assert(exception->signature == MagickSignature); 887 image=AcquireImage(image_info); 888 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception); 889 if (status == MagickFalse) 890 { 891 image=DestroyImageList(image); 892 return((Image *) NULL); 893 } 894 /* 895 Read MGK image. 896 */ 897 (void) ReadBlobString(image,buffer); /* read magic number */ 898 if (IsMGK(buffer,7) == MagickFalse) 899 ThrowReaderException(CorruptImageError,"ImproperImageHeader"); 900 (void) ReadBlobString(image,buffer); 901 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows); 902 if (count <= 0) 903 ThrowReaderException(CorruptImageError,"ImproperImageHeader"); 904 do 905 { 906 /* 907 Initialize image structure. 908 */ 909 image->columns=columns; 910 image->rows=rows; 911 image->depth=8; 912 if ((image_info->ping != MagickFalse) && (image_info->number_scenes != 0)) 913 if (image->scene >= (image_info->scene+image_info->number_scenes-1)) 914 break; 915 /* 916 Convert MGK raster image to pixel packets. 917 */ 918 if (SetImageExtent(image,0,0) == MagickFalse) 919 { 920 InheritException(exception,&image->exception); 921 return(DestroyImageList(image)); 922 } 923 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns,3UL*sizeof(*pixels)); 924 if (pixels == (unsigned char *) NULL) 925 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed"); 926 for (y=0; y < (ssize_t) image->rows; y++) 927 { 928 count=(ssize_t) ReadBlob(image,(size_t) (3*image->columns),pixels); 929 if (count != (ssize_t) (3*image->columns)) 930 ThrowReaderException(CorruptImageError,"UnableToReadImageData"); 931 p=pixels; 932 q=QueueAuthenticPixels(image,0,y,image->columns,1,exception); 933 if (q == (PixelPacket *) NULL) 934 break; 935 for (x=0; x < (ssize_t) image->columns; x++) 936 { 937 SetPixelRed(q,ScaleCharToQuantum(*p++)); 938 SetPixelGreen(q,ScaleCharToQuantum(*p++)); 939 SetPixelBlue(q,ScaleCharToQuantum(*p++)); 940 q++; 941 } 942 if (SyncAuthenticPixels(image,exception) == MagickFalse) 943 break; 944 if ((image->previous == (Image *) NULL) && 945 (SetImageProgress(image,LoadImageTag,y,image>>rows) == MagickFalse)) 946 break; 947 } 948 pixels=(unsigned char *) RelinquishMagickMemory(pixels); 949 if (EOFBlob(image) != MagickFalse) 950 { 951 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image->filename); 952 break; 953 } 954 /* 955 Proceed to next image. 956 */ 957 if (image_info->number_scenes != 0) 958 if (image->scene >= (image_info->scene+image_info->number_scenes-1)) 959 break; 960 *buffer='\0'; 961 (void) ReadBlobString(image,buffer); 962 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows); 963 if (count != 0) 964 { 965 /* 966 Allocate next image structure. 967 */ 968 AcquireNextImage(image_info,image); 969 if (GetNextImageInList(image) == (Image *) NULL) 970 { 971 image=DestroyImageList(image); 972 return((Image *) NULL); 973 } 974 image=SyncNextImageInList(image); 975 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image)); 976 if (status == MagickFalse) 977 break; 978 } 979 } while (count != 0); 980 (void) CloseBlob(image); 981 return(GetFirstImageInList(image)); 982 } 983 984 /* 985 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 986 % % 987 % % 988 % % 989 % R e g i s t e r M G K I m a g e % 990 % % 991 % % 992 % % 993 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 994 % 995 % RegisterMGKImage() adds attributes for the MGK image format to 996 % the list of supported formats. The attributes include the image format 997 % tag, a method to read and/or write the format, whether the format 998 % supports the saving of more than one frame to the same file or blob, 999 % whether the format supports native in-memory I/O, and a brief 1000 % description of the format. 1001 % 1002 % The format of the RegisterMGKImage method is: 1003 % 1004 % unsigned long RegisterMGKImage(void) 1005 % 1006 */ 1007 ModuleExport unsigned long RegisterMGKImage(void) 1008 { 1009 MagickInfo 1010 *entry; 1011 1012 entry=SetMagickInfo("MGK"); 1013 entry->decoder=(DecodeImageHandler *) ReadMGKImage; 1014 entry->encoder=(EncodeImageHandler *) WriteMGKImage; 1015 entry->magick=(IsImageFormatHandler *) IsMGK; 1016 entry->description=ConstantString("MGK"); 1017 entry->module=ConstantString("MGK"); 1018 (void) RegisterMagickInfo(entry); 1019 return(MagickImageCoderSignature); 1020 } 1021 1022 /* 1023 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1024 % % 1025 % % 1026 % % 1027 % U n r e g i s t e r M G K I m a g e % 1028 % % 1029 % % 1030 % % 1031 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1032 % 1033 % UnregisterMGKImage() removes format registrations made by the 1034 % MGK module from the list of supported formats. 1035 % 1036 % The format of the UnregisterMGKImage method is: 1037 % 1038 % UnregisterMGKImage(void) 1039 % 1040 */ 1041 ModuleExport void UnregisterMGKImage(void) 1042 { 1043 (void) UnregisterMagickInfo("MGK"); 1044 } 1045 1046 /* 1047 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1048 % % 1049 % % 1050 % % 1051 % W r i t e M G K I m a g e % 1052 % % 1053 % % 1054 % % 1055 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1056 % 1057 % WriteMGKImage() writes an image to a file in red, green, and blue 1058 % MGK rasterfile format. 1059 % 1060 % The format of the WriteMGKImage method is: 1061 % 1062 % MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image) 1063 % 1064 % A description of each parameter follows. 1065 % 1066 % o image_info: the image info. 1067 % 1068 % o image: The image. 1069 % 1070 */ 1071 static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image) 1072 { 1073 char 1074 buffer[MaxTextExtent]; 1075 1076 MagickBooleanType 1077 status; 1078 1079 MagickOffsetType 1080 scene; 1081 1082 register const PixelPacket 1083 *p; 1084 1085 register ssize_t 1086 x; 1087 1088 register unsigned char 1089 *q; 1090 1091 ssize_t 1092 y; 1093 1094 unsigned char 1095 *pixels; 1096 1097 /* 1098 Open output image file. 1099 */ 1100 assert(image_info != (const ImageInfo *) NULL); 1101 assert(image_info->signature == MagickSignature); 1102 assert(image != (Image *) NULL); 1103 assert(image->signature == MagickSignature); 1104 if (image->debug != MagickFalse) 1105 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename); 1106 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&image->exception); 1107 if (status == MagickFalse) 1108 return(status); 1109 scene=0; 1110 do 1111 { 1112 /* 1113 Allocate memory for pixels. 1114 */ 1115 if (image->colorspace != RGBColorspace) 1116 (void) SetImageColorspace(image,RGBColorspace); 1117 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns, 1118 3UL*sizeof(*pixels)); 1119 if (pixels == (unsigned char *) NULL) 1120 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed"); 1121 /* 1122 Initialize raster file header. 1123 */ 1124 (void) WriteBlobString(image,"id=mgk\n"); 1125 (void) FormatLocaleString(buffer,MaxTextExtent,"%lu %lu\n", 1126 image->columns,image->rows); 1127 (void) WriteBlobString(image,buffer); 1128 for (y=0; y < (ssize_t) image->rows; y++) 1129 { 1130 p=GetVirtualPixels(image,0,y,image->columns,1,&image->exception); 1131 if (p == (const PixelPacket *) NULL) 1132 break; 1133 q=pixels; 1134 for (x=0; x < (ssize_t) image->columns; x++) 1135 { 1136 *q++=ScaleQuantumToChar(GetPixelRed(p)); 1137 *q++=ScaleQuantumToChar(GetPixelGreen(p)); 1138 *q++=ScaleQuantumToChar(GetPixelBlue(p)); 1139 p++; 1140 } 1141 (void) WriteBlob(image,(size_t) (q-pixels),pixels); 1142 if ((image->previous == (Image *) NULL) && 1143 (SetImageProgress(image,SaveImageTag,y,image->rows) == MagickFalse)) 1144 break; 1145 } 1146 pixels=(unsigned char *) RelinquishMagickMemory(pixels); 1147 if (GetNextImageInList(image) == (Image *) NULL) 1148 break; 1149 image=SyncNextImageInList(image); 1150 status=SetImageProgress(image,SaveImagesTag,scene, 1151 GetImageListLength(image)); 1152 if (status == MagickFalse) 1153 break; 1154 scene++; 1155 } while (image_info->adjoin != MagickFalse); 1156 (void) CloseBlob(image); 1157 return(MagickTrue); 1158 }</pre> 1159 1160 <p>To invoke the custom coder from the command line, use these commands:</p> 1161 1162 <pre>convert logo: logo.mgk 1163 display logo.mgk 1164 </pre> 1165 1166 <p>We provide the <a href="http://www.imagemagick.org/download/kits/">Magick Coder Kit</a> to help you get started writing your own custom coder.</p> 1167 1168 <h2 class="magick-header"><a id="filters"></a>Custom Image Filters</h2> 1169 1170 <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="command-line-options.php#process">-process</a> option or from the MagickCore API method <a href="../api/module.php#ExecuteModuleProcess">ExecuteModuleProcess()</a>.</p> 1171 1172 <p>Here is a listing of a sample <a href="../source/analyze.c">custom image filter</a>. It computes a few statistics such as the pixel brightness and saturation mean and standard-deviation.</p> 1173 1174 <pre class="pre-scrollable">#include <stdio.h> 1175 #include <stdlib.h> 1176 #include <string.h> 1177 #include <time.h> 1178 #include <assert.h> 1179 #include <math.h> 1180 #include "magick/MagickCore.h" 1181 1182 /* 1183 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1184 % % 1185 % % 1186 % % 1187 % a n a l y z e I m a g e % 1188 % % 1189 % % 1190 % % 1191 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1192 % 1193 % analyzeImage() computes the brightness and saturation mean, standard 1194 % deviation, kurtosis and skewness and stores these values as attributes 1195 % of the image. 1196 % 1197 % The format of the analyzeImage method is: 1198 % 1199 % size_t analyzeImage(Image *images,const int argc,char **argv, 1200 % ExceptionInfo *exception) 1201 % 1202 % A description of each parameter follows: 1203 % 1204 % o image: the address of a structure of type Image. 1205 % 1206 % o argc: Specifies a pointer to an integer describing the number of 1207 % elements in the argument vector. 1208 % 1209 % o argv: Specifies a pointer to a text array containing the command line 1210 % arguments. 1211 % 1212 % o exception: return any errors or warnings in this structure. 1213 % 1214 */ 1215 ModuleExport size_t analyzeImage(Image **images,const int argc,const char **argv, 1216 ExceptionInfo *exception) 1217 { 1218 char 1219 text[MaxTextExtent]; 1220 1221 double 1222 area, 1223 brightness, 1224 brightness_mean, 1225 brightness_standard_deviation, 1226 brightness_kurtosis, 1227 brightness_skewness, 1228 brightness_sum_x, 1229 brightness_sum_x2, 1230 brightness_sum_x3, 1231 brightness_sum_x4, 1232 hue, 1233 saturation, 1234 saturation_mean, 1235 saturation_standard_deviation, 1236 saturation_kurtosis, 1237 saturation_skewness, 1238 saturation_sum_x, 1239 saturation_sum_x2, 1240 saturation_sum_x3, 1241 saturation_sum_x4; 1242 1243 Image 1244 *image; 1245 1246 assert(images != (Image **) NULL); 1247 assert(*images != (Image *) NULL); 1248 assert((*images)->signature == MagickSignature); 1249 (void) argc; 1250 (void) argv; 1251 image=(*images); 1252 for ( ; image != (Image *) NULL; image=GetNextImageInList(image)) 1253 { 1254 CacheView 1255 *image_view; 1256 1257 MagickBooleanType 1258 status; 1259 1260 ssize_t 1261 y; 1262 1263 brightness_sum_x=0.0; 1264 brightness_sum_x2=0.0; 1265 brightness_sum_x3=0.0; 1266 brightness_sum_x4=0.0; 1267 brightness_mean=0.0; 1268 brightness_standard_deviation=0.0; 1269 brightness_kurtosis=0.0; 1270 brightness_skewness=0.0; 1271 saturation_sum_x=0.0; 1272 saturation_sum_x2=0.0; 1273 saturation_sum_x3=0.0; 1274 saturation_sum_x4=0.0; 1275 saturation_mean=0.0; 1276 saturation_standard_deviation=0.0; 1277 saturation_kurtosis=0.0; 1278 saturation_skewness=0.0; 1279 area=0.0; 1280 status=MagickTrue; 1281 image_view=AcquireVirtualCacheView(image,exception); 1282 #if defined(MAGICKCORE_OPENMP_SUPPORT) 1283 #pragma omp parallel for schedule(dynamic,4) shared(status) 1284 #endif 1285 for (y=0; y < (ssize_t) image->rows; y++) 1286 { 1287 register const PixelPacket 1288 *p; 1289 1290 register ssize_t 1291 x; 1292 1293 if (status == MagickFalse) 1294 continue; 1295 p=GetCacheViewVirtualPixels(image_view,0,y,image->columns,1,exception); 1296 if (p == (const PixelPacket *) NULL) 1297 { 1298 status=MagickFalse; 1299 continue; 1300 } 1301 for (x=0; x < (ssize_t) image->columns; x++) 1302 { 1303 ConvertRGBToHSB(GetPixelRed(p),GetPixelGreen(p),GetPixelBue(p),&hue,&saturation,&brightness); 1304 brightness*=QuantumRange; 1305 brightness_sum_x+=brightness; 1306 brightness_sum_x2+=brightness*brightness; 1307 brightness_sum_x3+=brightness*brightness*brightness; 1308 brightness_sum_x4+=brightness*brightness*brightness*brightness; 1309 saturation*=QuantumRange; 1310 saturation_sum_x+=saturation; 1311 saturation_sum_x2+=saturation*saturation; 1312 saturation_sum_x3+=saturation*saturation*saturation; 1313 saturation_sum_x4+=saturation*saturation*saturation*saturation; 1314 area++; 1315 p++; 1316 } 1317 } 1318 image_view=DestroyCacheView(image_view); 1319 if (area <= 0.0) 1320 break; 1321 brightness_mean=brightness_sum_x/area; 1322 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_mean); 1323 (void) SetImageProperty(image,"filter:brightness:mean",text); 1324 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/ 1325 area*brightness_sum_x/area)); 1326 (void) FormatLocaleString(text,MaxTextExtent,"%g", 1327 brightness_standard_deviation); 1328 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text); 1329 if (brightness_standard_deviation != 0) 1330 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean* 1331 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean* 1332 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean* 1333 brightness_mean*brightness_mean)/(brightness_standard_deviation* 1334 brightness_standard_deviation*brightness_standard_deviation* 1335 brightness_standard_deviation)-3.0; 1336 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_kurtosis); 1337 (void) SetImageProperty(image,"filter:brightness:kurtosis",text); 1338 if (brightness_standard_deviation != 0) 1339 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean* 1340 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean* 1341 brightness_mean)/(brightness_standard_deviation* 1342 brightness_standard_deviation*brightness_standard_deviation); 1343 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_skewness); 1344 (void) SetImageProperty(image,"filter:brightness:skewness",text); 1345 saturation_mean=saturation_sum_x/area; 1346 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_mean); 1347 (void) SetImageProperty(image,"filter:saturation:mean",text); 1348 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/ 1349 area*saturation_sum_x/area)); 1350 (void) FormatLocaleString(text,MaxTextExtent,"%g", 1351 saturation_standard_deviation); 1352 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text); 1353 if (saturation_standard_deviation != 0) 1354 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean* 1355 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean* 1356 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean* 1357 saturation_mean*saturation_mean)/(saturation_standard_deviation* 1358 saturation_standard_deviation*saturation_standard_deviation* 1359 saturation_standard_deviation)-3.0; 1360 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_kurtosis); 1361 (void) SetImageProperty(image,"filter:saturation:kurtosis",text); 1362 if (saturation_standard_deviation != 0) 1363 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean* 1364 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean* 1365 saturation_mean)/(saturation_standard_deviation* 1366 saturation_standard_deviation*saturation_standard_deviation); 1367 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_skewness); 1368 (void) SetImageProperty(image,"filter:saturation:skewness",text); 1369 } 1370 return(MagickImageFilterSignature); 1371 }</pre> 1372 1373 <p>To invoke the custom filter from the command line, use this command:</p> 1374 1375 <pre>convert logo: -process \"analyze\" -verbose info: 1376 Image: logo: 1377 Format: LOGO (ImageMagick Logo) 1378 Class: PseudoClass 1379 Geometry: 640x480 1380 ... 1381 filter:brightness:kurtosis: 8.17947 1382 filter:brightness:mean: 60632.1 1383 filter:brightness:skewness: -2.97118 1384 filter:brightness:standard-deviation: 13742.1 1385 filter:saturation:kurtosis: 4.33554 1386 filter:saturation:mean: 5951.55 1387 filter:saturation:skewness: 2.42848 1388 filter:saturation:standard-deviation: 15575.9 1389 </pre> 1390 1391 1392 <p>We provide the <a href="http://www.imagemagick.org/download/kits/">Magick Filter Kit</a> to help you get started writing your own custom image filter.</p> 1393 1394 </div> 1395 <footer class="magick-footer"> 1396 <p><a href="support.php">Donate</a> 1397 <a href="sitemap.php">Sitemap</a> 1398 <a href="links.php">Related</a> 1399 <a href="architecture.php">Architecture</a> 1400 </p> 1401 <p><a href="architecture.php#">Back to top</a> 1402 <a href="http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> 1403 <a href="contact.php">Contact Us</a></p> 1404 <p><small> 1999-2016 ImageMagick Studio LLC</small></p> 1405 </footer> 1406 </div><!-- /.container --> 1407 1408 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script> 1409 <script src="http://nextgen.imagemagick.org/js/magick.php"></script> 1410 </div> 1411 </body> 1412 </html> 1413
