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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> 87 88 <h2><a class="anchor" id="overview"></a>Architecture Overview</h2> 89 90 <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> 91 92 <ul> 93 <li>colorspace (e.g sRGB, linear RGB, linear GRAY, CMYK, YUV, Lab, etc.)</li> 94 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li> 95 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li> 96 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li> 97 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li> 98 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li> 99 </ul> 100 101 <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> 102 103 <p>An efficient implementation of an image processing algorithm may require we get or set:</p> 104 105 <ul> 106 <li>one pixel a time (e.g. pixel at location 10,3)</li> 107 <li>a single scanline (e.g. all pixels from row 4)</li> 108 <li>a few scanlines at once (e.g. pixel rows 4-7)</li> 109 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li> 110 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li> 111 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li> 112 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li> 113 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li> 114 <li>a pixel component that is unsigned (65311) or in a floating-point representation (e.g. 0.17836)</li> 115 <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> 116 <li>one or more pixels simultaneously in different threads of execution</li> 117 <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> 118 <li>traits associated with each channel to specify whether the pixel channel is copied, updated, or blended</li> 119 <li>masks that define which pixels are eligible to be updated</li> 120 <li>extra channels that benefits the user but otherwise remain untouched by ImageMagick image processing algorithms</li> 121 </ul> 122 123 <p>Given the varied image formats and image processing requirements, we implemented the ImageMagick <a href="architecture.html#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.html#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.html#virtual-pixels">virtual pixels</a>).</p> 124 125 <p>In addition to pixels, images have a plethora of <a href="architecture.html#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> 126 127 <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.html#threads">thread</a> of execution. In the final sections, we discuss <a href="architecture.html#coders">image coders</a> to read or write a particular image format followed by a few words on creating a <a href="architecture.html#filters">filter</a> to access or update pixels based on your custom requirements.</p> 128 129 <h2><a class="anchor" id="cache"></a>The Pixel Cache</h2> 130 131 <p>The ImageMagick pixel cache is a repository for image pixels with up to 32 channels. The channels are stored contiguously 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 32-bit floating-bit <a href="high-dynamic-range.html">high dynamic-range</a> quantities. The channels can hold any value but typically contain red, green, blue, and alpha intensities or cyan, magenta, yellow, black and alpha intensities. A channel might contain the colormap indexes for colormapped images or the black channel for CMYK images. The pixel cache storage may be heap 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> 132 133 <h3>Create the Pixel Cache</h3> 134 135 <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> 136 137 <dl> 138 <dt class="col-md-8">Create an image canvas initialized to the background color:</dt><br/> 139 <dd class="col-md-8"><pre class="highlight"><code>image=AllocateImage(image_info); 140 if (SetImageExtent(image,640,480) == MagickFalse) 141 { /* an exception was thrown */ } 142 (void) QueryMagickColor("red",&image->background_color,&image->exception); 143 SetImageBackgroundColor(image); 144 </code></pre></dd> 145 146 <dt class="col-md-8">Create an image from a JPEG image on disk:</dt><br/> 147 <dd class="col-md-8"><pre class="highlight"><code>(void) strcpy(image_info->filename,"image.jpg"): 148 image=ReadImage(image_info,exception); 149 if (image == (Image *) NULL) 150 { /* an exception was thrown */ } 151 </code></pre></dd> 152 <dt class="col-md-8">Create an image from a memory based image:</dt><br/> 153 <dd class="col-md-8"><pre class="highlight"><code>image=BlobToImage(blob_info,blob,extent,exception); 154 if (image == (Image *) NULL) 155 { /* an exception was thrown */ } 156 </code></pre></dd> 157 </dl> 158 159 <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> 160 161 <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 8-bit gray 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.html#version">‑version</a> option: </p> 162 163 <pre class="highlight"><span class="crtprompt">$ </span><span class='crtin'>identify -version</span><span class='crtout'><br/></span><span class="crtprompt">$ </span><span class='crtin'>Version: ImageMagick 7.0.8-23 2018-12-25 Q16 https://imagemagick.org</span></pre> 164 <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 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> 165 166 <h3><a class="anchor" id="authentic-pixels"></a>Access the Pixel Cache</h3> 167 168 <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.html#authentic-pixels">authentic pixels</a> and outside the region as <a href="architecture.html#virtual-pixels">virtual pixels</a>. Use these methods to access the pixels in the cache:</p> 169 <ul> 170 <li><a href="api/cache.html#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> 171 <li><a href="api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a>: gets pixels that you intend to modify</li> 172 <li><a href="api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a>: queue pixels that you intend to set</li> 173 <li><a href="api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a>: update the pixel cache with any modified pixels</li> 174 </ul> 175 176 <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> 177 178 <pre class="pre-scrollable"><code>const Quantum 179 *p; 180 181 Quantum 182 *q; 183 184 ssize_t 185 x, 186 y; 187 188 destination=CloneImage(source,source->columns,source->rows,MagickTrue, 189 exception); 190 if (destination == (Image *) NULL) 191 { /* an exception was thrown */ } 192 for (y=0; y < (ssize_t) source->rows; y++) 193 { 194 p=GetVirtualPixels(source,0,y,source->columns,1,exception); 195 q=GetAuthenticPixels(destination,0,y,destination->columns,1,exception); 196 if ((p == (const Quantum *) NULL) || (q == (Quantum *) NULL) 197 break; 198 for (x=0; x < (ssize_t) source->columns; x++) 199 { 200 SetPixelRed(image,90*p->red/100,q); 201 SetPixelGreen(image,90*p->green/100,q); 202 SetPixelBlue(image,90*p->blue/100,q); 203 SetPixelAlpha(image,90*p->opacity/100,q); 204 p+=GetPixelChannels(source); 205 q+=GetPixelChannels(destination); 206 } 207 if (SyncAuthenticPixels(destination,exception) == MagickFalse) 208 break; 209 } 210 if (y < (ssize_t) source->rows) 211 { /* an exception was thrown */ } 212 </code></pre> 213 214 <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.html#GetAuthenticPixels">GetAuthenticPixels()</a> or <a href="api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a>. Use <a href="api/cache.html#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.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p> 215 216 <p>You can associate arbitrary content with each pixel, called <em>meta</em> content. Use <a href="api/cache.html#GetVirtualMetacontent">GetVirtualMetacontent()</a> (to read the content) or <a href="api/cache.html#GetAuthenticMetacontent">GetAuthenticMetacontent()</a> (to update the content) to gain access to this content. For example, to print the metacontent, use:</p> 217 218 <pre class="highlight"><code>const void 219 *metacontent; 220 221 for (y=0; y < (ssize_t) source->rows; y++) 222 { 223 p=GetVirtualPixels(source,0,y,source->columns,1); 224 if (p == (const Quantum *) NULL) 225 break; 226 metacontent=GetVirtualMetacontent(source); 227 /* print meta content here */ 228 } 229 if (y < (ssize_t) source->rows) 230 /* an exception was thrown */ 231 </code></pre> 232 233 <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> 234 235 <pre class="highlight"><code>p=GetVirtualPixels(source,-3,-3,source->columns+3,6,exception); 236 </code></pre> 237 238 <p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p> 239 240 <h3><a class="anchor" id="virtual-pixels"></a>Virtual Pixels</h3> 241 242 <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> 243 <p>Access to the virtual pixels are controlled by the <a href="api/cache.html#SetImageVirtualPixelMethod">SetImageVirtualPixelMethod()</a> method from the MagickCore API or the <a href="command-line-options.html#virtual-pixel">‑virtual‑pixel</a> option from the command line. The methods include:</p> 244 245 <dl class="row"> 246 <dt class="col-md-4">background</dt> 247 <dd class="col-md-8">the area surrounding the image is the background color</dd> 248 <dt class="col-md-4">black</dt> 249 <dd class="col-md-8">the area surrounding the image is black</dd> 250 <dt class="col-md-4">checker-tile</dt> 251 <dd class="col-md-8">alternate squares with image and background color</dd> 252 <dt class="col-md-4">dither</dt> 253 <dd class="col-md-8">non-random 32x32 dithered pattern</dd> 254 <dt class="col-md-4">edge</dt> 255 <dd class="col-md-8">extend the edge pixel toward infinity (default)</dd> 256 <dt class="col-md-4">gray</dt> 257 <dd class="col-md-8">the area surrounding the image is gray</dd> 258 <dt class="col-md-4">horizontal-tile</dt> 259 <dd class="col-md-8">horizontally tile the image, background color above/below</dd> 260 <dt class="col-md-4">horizontal-tile-edge</dt> 261 <dd class="col-md-8">horizontally tile the image and replicate the side edge pixels</dd> 262 <dt class="col-md-4">mirror</dt> 263 <dd class="col-md-8">mirror tile the image</dd> 264 <dt class="col-md-4">random</dt> 265 <dd class="col-md-8">choose a random pixel from the image</dd> 266 <dt class="col-md-4">tile</dt> 267 <dd class="col-md-8">tile the image</dd> 268 <dt class="col-md-4">transparent</dt> 269 <dd class="col-md-8">the area surrounding the image is transparent blackness</dd> 270 <dt class="col-md-4">vertical-tile</dt> 271 <dd class="col-md-8">vertically tile the image, sides are background color</dd> 272 <dt class="col-md-4">vertical-tile-edge</dt> 273 <dd class="col-md-8">vertically tile the image and replicate the side edge pixels</dd> 274 <dt class="col-md-4">white</dt> 275 <dd class="col-md-8">the area surrounding the image is white</dd> 276 </dl> 277 278 279 <h3>Cache Storage and Resource Requirements</h3> 280 281 <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 non-HDRI 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, we create the pixel cache on disk and attempt to memory-map it. 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> 282 283 <dl class="row"> 284 <dt class="col-md-4">width</dt> 285 <dd class="col-md-8">maximum width of an image. Exceed this limit and an exception is thrown and processing stops.</dd> 286 <dt class="col-md-4">height</dt> 287 <dd class="col-md-8">maximum height of an image. Exceed this limit and an exception is thrown and processing stops.</dd> 288 <dt class="col-md-4">area</dt> 289 <dd class="col-md-8">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> 290 <dt class="col-md-4">memory</dt> 291 <dd class="col-md-8">maximum amount of memory in bytes to allocate for the pixel cache from the heap.</dd> 292 <dt class="col-md-4">map</dt> 293 <dd class="col-md-8">maximum amount of memory map in bytes to allocate for the pixel cache.</dd> 294 <dt class="col-md-4">disk</dt> 295 <dd class="col-md-8">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> 296 <dt class="col-md-4">files</dt> 297 <dd class="col-md-8">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> 298 <dt class="col-md-4">thread</dt> 299 <dd class="col-md-8">maximum number of threads that are permitted to run in parallel.</dd> 300 <dt class="col-md-4">time</dt> 301 <dd class="col-md-8">maximum number of seconds that the process is permitted to execute. Exceed this limit and an exception is thrown and processing stops.</dd> 302 </dl> 303 304 <p>Note, these limits pertain to the ImageMagick pixel cache. Certain algorithms within ImageMagick do not respect these limits nor does any of the external delegate libraries (e.g. JPEG, TIFF, etc.).</p> 305 306 <p>To determine the current setting of these limits, use this command:</p> 307 <pre class="highlight">-> identify -list resource 308 Resource limits: 309 Width: 100MP 310 Height: 100MP 311 Area: 25.181GB 312 Memory: 11.726GiB 313 Map: 23.452GiB 314 Disk: unlimited 315 File: 768 316 Thread: 12 317 Throttle: 0 318 Time: unlimited 319 </pre> 320 321 <p>You can set these limits either as a <a href="security-policy.html">security policy</a> (see <a href="https://imagemagick.org/source/policy.xml">policy.xml</a>), with an <a href="resources.html#environment">environment variable</a>, with the <a href="command-line-options.html#limit">-limit</a> command line option, or with the <a href="api/resource.html#SetMagickResourceLimit">SetMagickResourceLimit()</a> MagickCore API method. As an example, our online web interface to ImageMagick, <a href="../MagickStudio/scripts/MagickStudio.cgi">ImageMagick Studio</a>, includes these policy limits to help prevent a denial-of-service:</p> 322 <pre class="highlight"><code><policymap> 323 <policy domain="resource" name="temporary-path" value="/tmp"/> 324 <policy domain="resource" name="memory" value="256MiB"/> 325 <policy domain="resource" name="map" value="512MiB"/> 326 <policy domain="resource" name="width" value="8KP"/> 327 <policy domain="resource" name="height" value="8KP"/> 328 <policy domain="resource" name="area" value="128MB"/> 329 <policy domain="resource" name="disk" value="1GiB"/> 330 <policy domain="resource" name="file" value="768"/> 331 <policy domain="resource" name="thread" value="2"/> 332 <policy domain="resource" name="throttle" value="0"/> 333 <policy domain="resource" name="time" value="120"/> 334 <policy domain="system" name="precision" value="6"/> 335 <policy domain="cache" name="shared-secret" value="replace with your secret phrase" stealth="true"/> 336 <policy domain="delegate" rights="none" pattern="HTTPS" /> 337 <policy domain="path" rights="none" pattern="@*"/> <!-- indirect reads not permitted --> 338 </policymap> 339 </code></pre> 340 <p>Since we process multiple simultaneous sessions, we don't want any one session consuming all the available memory.With this policy, 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. If any one image has a width or height that exceeds 8192 pixels, an exception is thrown and processing stops. As of ImageMagick 7.0.1-8 you can prevent the use of any delegate or all delegates (set the pattern to "*"). Note, prior to this release, use a domain of "coder" to prevent delegate usage (e.g. domain="coder" rights="none" pattern="HTTPS"). The policy also prevents indirect reads. If you want to, for example, read text from a file (e.g. caption:@myCaption.txt), you'll need to remove this policy.</p> 341 342 <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> 343 344 <p>To determine which type and how much resources are consumed by the pixel cache, add the <a href="command-line-options.html#debug">-debug cache</a> option to the command-line:</p> 345 <pre class="highlight">-> convert -debug cache logo: -sharpen 3x2 null: 346 2016-12-17T13:33:42-05:00 0:00.000 0.000u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 347 destroy 348 2016-12-17T13:33:42-05:00 0:00.000 0.000u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 349 open LOGO[0] (Heap Memory, 640x480x4 4.688MiB) 350 2016-12-17T13:33:42-05:00 0:00.010 0.000u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 351 open LOGO[0] (Heap Memory, 640x480x3 3.516MiB) 352 2016-12-17T13:33:42-05:00 0:00.010 0.000u 7.0.0 Cache convert: cache.c/ClonePixelCachePixels/1044/Cache 353 Memory => Memory 354 2016-12-17T13:33:42-05:00 0:00.020 0.010u 7.0.0 Cache convert: cache.c/ClonePixelCachePixels/1044/Cache 355 Memory => Memory 356 2016-12-17T13:33:42-05:00 0:00.020 0.010u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 357 open LOGO[0] (Heap Memory, 640x480x3 3.516MiB) 358 2016-12-17T13:33:42-05:00 0:00.050 0.100u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 359 destroy LOGO[0] 360 2016-12-17T13:33:42-05:00 0:00.050 0.100u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 361 destroy LOGO[0] 362 </pre> 363 <p>This command utilizes a pixel cache in memory. The logo consumed 4.688MiB and after it was sharpened, 3.516MiB.</p> 364 365 366 <h3>Distributed Pixel Cache</h3> 367 <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> 368 <pre class="highlight"><code>convert -distribute-cache 6668 & // start on 192.168.100.50 369 convert -define registry:cache:hosts=192.168.100.50:6668 myimage.jpg -sharpen 5x2 mimage.png 370 </code></pre> 371 372 <h3>Cache Views</h3> 373 374 <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.html">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> 375 <pre class="pre-scrollable"><code>CacheView 376 *view_1, 377 *view_2; 378 379 view_1=AcquireVirtualCacheView(source,exception); 380 view_2=AcquireVirtualCacheView(source,exception); 381 for (y=0; y < (ssize_t) source->rows; y++) 382 { 383 u=GetCacheViewVirtualPixels(view_1,0,y,source->columns,1,exception); 384 v=GetCacheViewVirtualPixels(view_2,0,source->rows-y-1,source->columns,1,exception); 385 if ((u == (const Quantum *) NULL) || (v == (const Quantum *) NULL)) 386 break; 387 for (x=0; x < (ssize_t) source->columns; x++) 388 { 389 /* do something with u & v here */ 390 } 391 } 392 view_2=DestroyCacheView(view_2); 393 view_1=DestroyCacheView(view_1); 394 if (y < (ssize_t) source->rows) 395 { /* an exception was thrown */ } 396 </code></pre> 397 398 <h3>Magick Persistent Cache Format</h3> 399 400 <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> 401 <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> 402 403 <h3>Best Practices</h3> 404 405 <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> 406 407 <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> 408 409 <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> 410 411 <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> 412 413 <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.html#threads">thread of execution</a> is accessing the image.</p> 414 415 <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> 416 417 <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.</p> 418 419 <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> 420 421 <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.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 have unexpected results due to out-of-band pixel values than the non-HDRI version.</p> 422 423 <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> 424 <pre class="highlight"><code>convert -limit memory 2GB -limit map 4GB -define registry:temporary-path=/data/tmp ... 425 </code></pre> 426 427 <p>Set global resource limits for your environment in the <code>policy.xml</code> configuration file.</p> 428 429 <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> 430 <pre class="highlight"><code>convert image.tif image.mpc 431 convert image.mpc -crop 100x100+0+0 +repage 1.png 432 convert image.mpc -crop 100x100+100+0 +repage 2.png 433 convert image.mpc -crop 100x100+200+0 +repage 3.png 434 </code></pre> 435 436 <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="../MagickStudio/scripts/MagickStudio.cgi">online image studio</a>.</p> 437 438 <h2><a class="anchor" id="stream"></a>Streaming Pixels</h2> 439 440 <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> 441 442 <p>Use <a href="api/stream.html#ReadStream">ReadStream()</a> or <a href="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> 443 <pre class="pre-scrollable"><code>static size_t StreamPixels(const Image *image,const void *pixels,const size_t columns) 444 { 445 register const Quantum 446 *p; 447 448 MyData 449 *my_data; 450 451 my_data=(MyData *) image->client_data; 452 p=(Quantum *) pixels; 453 if (p != (const Quantum *) NULL) 454 { 455 /* process pixels here */ 456 } 457 return(columns); 458 } 459 460 ... 461 462 /* invoke the pixel stream here */ 463 image_info->client_data=(void *) MyData; 464 image=ReadStream(image_info,&StreamPixels,exception); 465 </code></pre> 466 467 <p>We also provide a lightweight tool, <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 href="../www/stream.html">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> 468 469 <h2><a class="anchor" id="properties"></a>Image Properties and Profiles</h2> 470 471 <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> 472 <pre class="highlight"><code>(void) printf("image width: %lu, height: %lu\n",image->columns,image->rows); 473 </code></pre> 474 475 <p>For a great majority of image properties, such as an image comment or description, we use the <a href="api/property.html#GetImageProperty">GetImageProperty()</a> and <a href="api/property.html#SetImageProperty">SetImageProperty()</a> methods. Here we set a property and fetch it right back:</p> 476 <pre class="highlight"><code>const char 477 *comment; 478 479 (void) SetImageProperty(image,"comment","This space for rent"); 480 comment=GetImageProperty(image,"comment"); 481 if (comment == (const char *) NULL) 482 (void) printf("Image comment: %s\n",comment); 483 </code></pre> 484 485 <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> 486 487 <p>Image profiles are handled with <a href="api/profile.html#GetImageProfile">GetImageProfile()</a>, <a href="api/profile.html#SetImageProfile">SetImageProfile()</a>, and <a href="api/profile.html#ProfileImage">ProfileImage()</a> methods. Here we set a profile and fetch it right back:</p> 488 <pre class="highlight"><code>StringInfo 489 *profile; 490 491 profile=AcquireStringInfo(length); 492 SetStringInfoDatum(profile,my_exif_profile); 493 (void) SetImageProfile(image,"EXIF",profile); 494 DestroyStringInfo(profile); 495 profile=GetImageProfile(image,"EXIF"); 496 if (profile != (StringInfo *) NULL) 497 (void) PrintStringInfo(stdout,"EXIF",profile); 498 </code></pre> 499 500 <h2><a class="anchor" id="tera-pixel"></a>Large Image Support</h2> 501 <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> 502 <pre class="highlight"><code>convert logo: -resize 250000x250000 logo.miff 503 </code></pre> 504 505 <p>For large images, memory resources will likely be exhausted and ImageMagick will instead 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> 506 <pre class="highlight"><code>convert -define registry:temporary-path=/data/tmp logo: \ <br/> -resize 250000x250000 logo.miff 507 </code></pre> 508 509 <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> 510 <pre class="highlight"><code>convert -define registry:temporary-path=/data/tmp -limit memory 16mb \ 511 logo: -resize 250000x250000 logo.miff 512 </code></pre> 513 514 <p>Here we force all image pixels to disk:</p> 515 <pre class="highlight"><code>convert -define registry:temporary-path=/data/tmp -limit area 0 \ 516 logo: -resize 250000x250000 logo.miff 517 </code></pre> 518 519 <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> 520 <pre class="highlight"><code>convert -monitor -limit memory 2GiB -limit map 4GiB -define registry:temporary-path=/data/tmp \ 521 logo: -resize 250000x250000 logo.miff 522 </code></pre> 523 524 <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> 525 <pre class="highlight"><code>convert -distribute-cache 6668 & // start on 192.168.100.50 526 convert -distribute-cache 6668 & // start on 192.168.100.51 527 convert -limit memory 2mb -limit map 2mb -limit disk 2gb \ 528 -define registry:cache:hosts=192.168.100.50:6668,192.168.100.51:6668 \ 529 myhugeimage.jpg -sharpen 5x2 myhugeimage.png 530 </code></pre> 531 <p>Due to network latency, expect a substantial slow-down in processing your workflow.</p> 532 533 <h2><a class="anchor" id="threads"></a>Threads of Execution</h2> 534 535 <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.html#CompositeImage">CompositeImage()</a> method, for example. Suppose we want to composite a single source image over a different destination 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> 536 537 <p>Here is an MagickCore code snippet that takes advantage of threads of execution with the <a href="../www/openmp.html">OpenMP</a> programming paradigm:</p> 538 <pre class="pre-scrollable"><code>CacheView 539 *image_view; 540 541 MagickBooleanType 542 status; 543 544 ssize_t 545 y; 546 547 status=MagickTrue; 548 image_view=AcquireVirtualCacheView(image,exception); 549 #pragma omp parallel for schedule(static,4) shared(status) 550 for (y=0; y < (ssize_t) image->rows; y++) 551 { 552 register Quantum 553 *q; 554 555 register ssize_t 556 x; 557 558 register void 559 *metacontent; 560 561 if (status == MagickFalse) 562 continue; 563 q=GetCacheViewAuthenticPixels(image_view,0,y,image->columns,1,exception); 564 if (q == (Quantum *) NULL) 565 { 566 status=MagickFalse; 567 continue; 568 } 569 metacontent=GetCacheViewAuthenticMetacontent(image_view); 570 for (x=0; x < (ssize_t) image->columns; x++) 571 { 572 SetPixelRed(image,...,q); 573 SetPixelGreen(image,...,q); 574 SetPixelBlue(image,...,q); 575 SetPixelAlpha(image,...,q); 576 if (metacontent != NULL) 577 metacontent[indexes+x]=...; 578 q+=GetPixelChannels(image); 579 } 580 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse) 581 status=MagickFalse; 582 } 583 image_view=DestroyCacheView(image_view); 584 if (status == MagickFalse) 585 perror("something went wrong"); 586 </code></pre> 587 588 <p>This code snippet converts an uncompressed Windows bitmap to a Magick++ image:</p> 589 <pre class="pre-scrollable"><code>#include "Magick++.h" 590 #include <assert.h> 591 #include "omp.h" 592 593 void ConvertBMPToImage(const BITMAPINFOHEADER *bmp_info, 594 const unsigned char *restrict pixels,Magick::Image *image) 595 { 596 /* 597 Prepare the image so that we can modify the pixels directly. 598 */ 599 assert(bmp_info->biCompression == BI_RGB); 600 assert(bmp_info->biWidth == image->columns()); 601 assert(abs(bmp_info->biHeight) == image->rows()); 602 image->modifyImage(); 603 if (bmp_info->biBitCount == 24) 604 image->type(MagickCore::TrueColorType); 605 else 606 image->type(MagickCore::TrueColorMatteType); 607 register unsigned int bytes_per_row=bmp_info->biWidth*bmp_info->biBitCount/8; 608 if (bytes_per_row % 4 != 0) { 609 bytes_per_row=bytes_per_row+(4-bytes_per_row % 4); // divisible by 4. 610 } 611 /* 612 Copy all pixel data, row by row. 613 */ 614 #pragma omp parallel for 615 for (int y=0; y < int(image->rows()); y++) 616 { 617 int 618 row; 619 620 register const unsigned char 621 *restrict p; 622 623 register MagickCore::Quantum 624 *restrict q; 625 626 row=(bmp_info->biHeight > 0) ? (image->rows()-y-1) : y; 627 p=pixels+row*bytes_per_row; 628 q=image->setPixels(0,y,image->columns(),1); 629 for (int x=0; x < int(image->columns()); x++) 630 { 631 SetPixelBlue(image,p[0],q); 632 SetPixelGreen(image,p[1],q); 633 SetPixelRed(image,p[2],q); 634 if (bmp_info->biBitCount == 32) { 635 SetPixelAlpha(image,p[3],q); 636 } 637 q+=GetPixelChannels(image); 638 p+=bmp_info->biBitCount/8; 639 } 640 image->syncPixels(); // sync pixels to pixel cache. 641 } 642 return; 643 }</code></pre> 644 645 <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> 646 647 <p><a href="api/wand-view.html">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.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> 648 649 <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.html#configure">policy</a> or the <a href="resources.html#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="https://imagemagick.org/source/policy.xml">policy.xml</a> configuration file:</p> 650 <pre class="highlight"><code><policy domain="resource" name="thread" value="2"/> 651 </code></pre> 652 653 <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> 654 <pre class="highlight"><code>export MAGICK_THREAD_LIMIT=12 655 </code></pre> 656 657 <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> 658 659 <h5>Threading Performance</h5> 660 <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> 661 <pre class="highlight">-> convert -bench 10 model.png -sharpen 5x2 null: 662 Performance[1]: 10i 1.135ips 1.000e 8.760u 0:08.810 663 Performance[2]: 10i 2.020ips 0.640e 9.190u 0:04.950 664 Performance[3]: 10i 2.786ips 0.710e 9.400u 0:03.590 665 Performance[4]: 10i 3.378ips 0.749e 9.580u 0:02.960 666 Performance[5]: 10i 4.032ips 0.780e 9.580u 0:02.480 667 Performance[6]: 10i 4.566ips 0.801e 9.640u 0:02.190 668 Performance[7]: 10i 3.788ips 0.769e 10.980u 0:02.640 669 Performance[8]: 10i 4.115ips 0.784e 12.030u 0:02.430 670 Performance[9]: 10i 4.484ips 0.798e 12.860u 0:02.230 671 Performance[10]: 10i 4.274ips 0.790e 14.830u 0:02.340 672 Performance[11]: 10i 4.348ips 0.793e 16.500u 0:02.300 673 Performance[12]: 10i 4.525ips 0.799e 18.320u 0:02.210 674 </pre> 675 <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> 676 <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.html#environment">MAGICK_THREAD_LIMIT</a> environment variable, <a href="command-line-options.html#limit">-limit</a> command line option, or the <a href="resources.html#configure">policy.xml</a> configuration file.</p> 677 678 <h2><a class="anchor" id="distributed"></a>Heterogeneous Distributed Processing</h2> 679 <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> 680 681 <p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p> 682 <pre class="highlight"><code>identify -version 683 Features: DPC Cipher Modules OpenCL OpenMP 684 </code></pre> 685 686 <p>If so, run this command to realize a significant speed-up for image convolution:</p> 687 688 <pre class="highlight"><code>convert image.png -convolve '-1, -1, -1, -1, 9, -1, -1, -1, -1' convolve.png 689 </code></pre> 690 691 <p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p> 692 693 <p>Here is an example OpenCL kernel that convolves an image:</p> 694 <pre class="pre-scrollable"><code>static inline long ClampToCanvas(const long offset,const ulong range) 695 { 696 if (offset < 0L) 697 return(0L); 698 if (offset >= range) 699 return((long) (range-1L)); 700 return(offset); 701 } 702 703 static inline CLQuantum ClampToQuantum(const float value) 704 { 705 if (value < 0.0) 706 return((CLQuantum) 0); 707 if (value >= (float) QuantumRange) 708 return((CLQuantum) QuantumRange); 709 return((CLQuantum) (value+0.5)); 710 } 711 712 __kernel void Convolve(const __global CLPixelType *source,__constant float *filter, 713 const ulong width,const ulong height,__global CLPixelType *destination) 714 { 715 const ulong columns = get_global_size(0); 716 const ulong rows = get_global_size(1); 717 718 const long x = get_global_id(0); 719 const long y = get_global_id(1); 720 721 const float scale = (1.0/QuantumRange); 722 const long mid_width = (width-1)/2; 723 const long mid_height = (height-1)/2; 724 float4 sum = { 0.0, 0.0, 0.0, 0.0 }; 725 float gamma = 0.0; 726 register ulong i = 0; 727 728 for (long v=(-mid_height); v <= mid_height; v++) 729 { 730 for (long u=(-mid_width); u <= mid_width; u++) 731 { 732 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u, 733 columns); 734 const float alpha=scale*(QuantumRange-source[index].w); 735 sum.x+=alpha*filter[i]*source[index].x; 736 sum.y+=alpha*filter[i]*source[index].y; 737 sum.z+=alpha*filter[i]*source[index].z; 738 sum.w+=filter[i]*source[index].w; 739 gamma+=alpha*filter[i]; 740 i++; 741 } 742 } 743 744 gamma=1.0/(fabs(gamma) <= MagickEpsilon ? 1.0 : gamma); 745 const ulong index=y*columns+x; 746 destination[index].x=ClampToQuantum(gamma*sum.x); 747 destination[index].y=ClampToQuantum(gamma*sum.y); 748 destination[index].z=ClampToQuantum(gamma*sum.z); 749 destination[index].w=ClampToQuantum(sum.w); 750 };</code></pre> 751 752 <p>See <a href="https://github.com/ImageMagick/ImageMagick/tree/ImageMagick-7/magick/accelerate.c">magick/accelerate.c</a> for a complete implementation of image convolution with an OpenCL kernel.</p> 753 754 <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> 755 756 <h2><a class="anchor" id="coders"></a>Custom Image Coders</h2> 757 758 <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> 759 760 <p>Here is a listing of a sample <a href="https://imagemagick.org/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> 761 <pre class="pre-scrollable"><code>#include <MagickCore/studio.h> 762 #include <MagickCore/blob.h> 763 #include <MagickCore/cache.h> 764 #include <MagickCore/colorspace.h> 765 #include <MagickCore/exception.h> 766 #include <MagickCore/image.h> 767 #include <MagickCore/list.h> 768 #include <MagickCore/magick.h> 769 #include <MagickCore/memory_.h> 770 #include <MagickCore/monitor.h> 771 #include <MagickCore/pixel-accessor.h> 772 #include <MagickCore/string_.h> 773 #include <MagickCore/module.h> 774 #include "filter/blob-private.h" 775 #include "filter/exception-private.h" 776 #include "filter/image-private.h" 777 #include "filter/monitor-private.h" 778 #include "filter/quantum-private.h" 779 781 /* 782 Forward declarations. 783 */ 784 static MagickBooleanType 785 WriteMGKImage(const ImageInfo *,Image *,ExceptionInfo *); 786 788 /* 789 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 790 % % 791 % % 792 % % 793 % I s M G K % 794 % % 795 % % 796 % % 797 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 798 % 799 % IsMGK() returns MagickTrue if the image format type, identified by the 800 % magick string, is MGK. 801 % 802 % The format of the IsMGK method is: 803 % 804 % MagickBooleanType IsMGK(const unsigned char *magick,const size_t length) 805 % 806 % A description of each parameter follows: 807 % 808 % o magick: This string is generally the first few bytes of an image file 809 % or blob. 810 % 811 % o length: Specifies the length of the magick string. 812 % 813 */ 814 static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length) 815 { 816 if (length < 7) 817 return(MagickFalse); 818 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0) 819 return(MagickTrue); 820 return(MagickFalse); 821 } 822 824 /* 825 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 826 % % 827 % % 828 % % 829 % R e a d M G K I m a g e % 830 % % 831 % % 832 % % 833 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 834 % 835 % ReadMGKImage() reads a MGK image file and returns it. It allocates the 836 % memory necessary for the new Image structure and returns a pointer to the 837 % new image. 838 % 839 % The format of the ReadMGKImage method is: 840 % 841 % Image *ReadMGKImage(const ImageInfo *image_info, 842 % ExceptionInfo *exception) 843 % 844 % A description of each parameter follows: 845 % 846 % o image_info: the image info. 847 % 848 % o exception: return any errors or warnings in this structure. 849 % 850 */ 851 static Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception) 852 { 853 char 854 buffer[MaxTextExtent]; 855 856 Image 857 *image; 858 859 long 860 y; 861 862 MagickBooleanType 863 status; 864 865 register long 866 x; 867 868 register Quantum 869 *q; 870 871 register unsigned char 872 *p; 873 874 ssize_t 875 count; 876 877 unsigned char 878 *pixels; 879 880 unsigned long 881 columns, 882 rows; 883 884 /* 885 Open image file. 886 */ 887 assert(image_info != (const ImageInfo *) NULL); 888 assert(image_info->signature == MagickCoreSignature); 889 if (image_info->debug != MagickFalse) 890 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s", 891 image_info->filename); 892 assert(exception != (ExceptionInfo *) NULL); 893 assert(exception->signature == MagickCoreSignature); 894 image=AcquireImage(image_info,exception); 895 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception); 896 if (status == MagickFalse) 897 { 898 image=DestroyImageList(image); 899 return((Image *) NULL); 900 } 901 /* 902 Read MGK image. 903 */ 904 (void) ReadBlobString(image,buffer); /* read magic number */ 905 if (IsMGK(buffer,7) == MagickFalse) 906 ThrowReaderException(CorruptImageError,"ImproperImageHeader"); 907 (void) ReadBlobString(image,buffer); 908 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows); 909 if (count <= 0) 910 ThrowReaderException(CorruptImageError,"ImproperImageHeader"); 911 do 912 { 913 /* 914 Initialize image structure. 915 */ 916 image->columns=columns; 917 image->rows=rows; 918 image->depth=8; 919 if ((image_info->ping != MagickFalse) && (image_info->number_scenes != 0)) 920 if (image->scene >= (image_info->scene+image_info->number_scenes-1)) 921 break; 922 /* 923 Convert MGK raster image to pixel packets. 924 */ 925 if (SetImageExtent(image,image->columns,image->rows,exception) == MagickFalse) 926 return(DestroyImageList(image)); 927 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns, 928 3UL*sizeof(*pixels)); 929 if (pixels == (unsigned char *) NULL) 930 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed"); 931 for (y=0; y < (long) image->rows; y++) 932 { 933 count=(ssize_t) ReadBlob(image,(size_t) (3*image->columns),pixels); 934 if (count != (ssize_t) (3*image->columns)) 935 ThrowReaderException(CorruptImageError,"UnableToReadImageData"); 936 p=pixels; 937 q=QueueAuthenticPixels(image,0,y,image->columns,1,exception); 938 if (q == (Quantum *) NULL) 939 break; 940 for (x=0; x < (long) image->columns; x++) 941 { 942 SetPixelRed(image,ScaleCharToQuantum(*p++),q); 943 SetPixelGreen(image,ScaleCharToQuantum(*p++),q); 944 SetPixelBlue(image,ScaleCharToQuantum(*p++),q); 945 q+=GetPixelChannels(image); 946 } 947 if (SyncAuthenticPixels(image,exception) == MagickFalse) 948 break; 949 if (image->previous == (Image *) NULL) 950 if ((image->progress_monitor != (MagickProgressMonitor) NULL) && 951 (QuantumTick(y,image->rows) != MagickFalse)) 952 { 953 status=image->progress_monitor(LoadImageTag,y,image->rows, 954 image->client_data); 955 if (status == MagickFalse) 956 break; 957 } 958 } 959 pixels=(unsigned char *) RelinquishMagickMemory(pixels); 960 if (EOFBlob(image) != MagickFalse) 961 { 962 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile", 963 image->filename); 964 break; 965 } 966 /* 967 Proceed to next image. 968 */ 969 if (image_info->number_scenes != 0) 970 if (image->scene >= (image_info->scene+image_info->number_scenes-1)) 971 break; 972 *buffer='\0'; 973 (void) ReadBlobString(image,buffer); 974 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows); 975 if (count > 0) 976 { 977 /* 978 Allocate next image structure. 979 */ 980 AcquireNextImage(image_info,image,exception); 981 if (GetNextImageInList(image) == (Image *) NULL) 982 { 983 image=DestroyImageList(image); 984 return((Image *) NULL); 985 } 986 image=SyncNextImageInList(image); 987 if (image->progress_monitor != (MagickProgressMonitor) NULL) 988 { 989 status=SetImageProgress(image,LoadImageTag,TellBlob(image), 990 GetBlobSize(image)); 991 if (status == MagickFalse) 992 break; 993 } 994 } 995 } while (count > 0); 996 (void) CloseBlob(image); 997 return(GetFirstImageInList(image)); 998 } 999 1001 /* 1002 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1003 % % 1004 % % 1005 % % 1006 % R e g i s t e r M G K I m a g e % 1007 % % 1008 % % 1009 % % 1010 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1011 % 1012 % RegisterMGKImage() adds attributes for the MGK image format to 1013 % the list of supported formats. The attributes include the image format 1014 % tag, a method to read and/or write the format, whether the format 1015 % supports the saving of more than one frame to the same file or blob, 1016 % whether the format supports native in-memory I/O, and a brief 1017 % description of the format. 1018 % 1019 % The format of the RegisterMGKImage method is: 1020 % 1021 % unsigned long RegisterMGKImage(void) 1022 % 1023 */ 1024 ModuleExport unsigned long RegisterMGKImage(void) 1025 { 1026 MagickInfo 1027 *entry; 1028 1029 entry=AcquireMagickInfo("MGK","MGK","MGK image"); 1030 entry->decoder=(DecodeImageHandler *) ReadMGKImage; 1031 entry->encoder=(EncodeImageHandler *) WriteMGKImage; 1032 entry->magick=(IsImageFormatHandler *) IsMGK; 1033 (void) RegisterMagickInfo(entry); 1034 return(MagickImageCoderSignature); 1035 } 1036 1038 /* 1039 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1040 % % 1041 % % 1042 % % 1043 % U n r e g i s t e r M G K I m a g e % 1044 % % 1045 % % 1046 % % 1047 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1048 % 1049 % UnregisterMGKImage() removes format registrations made by the 1050 % MGK module from the list of supported formats. 1051 % 1052 % The format of the UnregisterMGKImage method is: 1053 % 1054 % UnregisterMGKImage(void) 1055 % 1056 */ 1057 ModuleExport void UnregisterMGKImage(void) 1058 { 1059 (void) UnregisterMagickInfo("MGK"); 1060 } 1061 1063 /* 1064 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1065 % % 1066 % % 1067 % % 1068 % W r i t e M G K I m a g e % 1069 % % 1070 % % 1071 % % 1072 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1073 % 1074 % WriteMGKImage() writes an image to a file in red, green, and blue MGK 1075 % rasterfile format. 1076 % 1077 % The format of the WriteMGKImage method is: 1078 % 1079 % MagickBooleanType WriteMGKImage(const ImageInfo *image_info, 1080 % Image *image) 1081 % 1082 % A description of each parameter follows. 1083 % 1084 % o image_info: the image info. 1085 % 1086 % o image: The image. 1087 % 1088 % o exception: return any errors or warnings in this structure. 1089 % 1090 */ 1091 static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image, 1092 ExceptionInfo *exception) 1093 { 1094 char 1095 buffer[MaxTextExtent]; 1096 1097 long 1098 y; 1099 1100 MagickBooleanType 1101 status; 1102 1103 MagickOffsetType 1104 scene; 1105 1106 register const Quantum 1107 *p; 1108 1109 register long 1110 x; 1111 1112 register unsigned char 1113 *q; 1114 1115 unsigned char 1116 *pixels; 1117 1118 /* 1119 Open output image file. 1120 */ 1121 assert(image_info != (const ImageInfo *) NULL); 1122 assert(image_info->signature == MagickCoreSignature); 1123 assert(image != (Image *) NULL); 1124 assert(image->signature == MagickCoreSignature); 1125 if (image->debug != MagickFalse) 1126 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename); 1127 status=OpenBlob(image_info,image,WriteBinaryBlobMode,exception); 1128 if (status == MagickFalse) 1129 return(status); 1130 scene=0; 1131 do 1132 { 1133 /* 1134 Allocate memory for pixels. 1135 */ 1136 if (image->colorspace != RGBColorspace) 1137 (void) SetImageColorspace(image,RGBColorspace,exception); 1138 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns, 1139 3UL*sizeof(*pixels)); 1140 if (pixels == (unsigned char *) NULL) 1141 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed"); 1142 /* 1143 Initialize raster file header. 1144 */ 1145 (void) WriteBlobString(image,"id=mgk\n"); 1146 (void) FormatLocaleString(buffer,MaxTextExtent,"%lu %lu\n",image->columns, 1147 image->rows); 1148 (void) WriteBlobString(image,buffer); 1149 for (y=0; y < (long) image->rows; y++) 1150 { 1151 p=GetVirtualPixels(image,0,y,image->columns,1,exception); 1152 if (p == (const Quantum *) NULL) 1153 break; 1154 q=pixels; 1155 for (x=0; x < (long) image->columns; x++) 1156 { 1157 *q++=ScaleQuantumToChar(GetPixelRed(image,p)); 1158 *q++=ScaleQuantumToChar(GetPixelGreen(image,p)); 1159 *q++=ScaleQuantumToChar(GetPixelBlue(image,p)); 1160 p+=GetPixelChannels(image); 1161 } 1162 (void) WriteBlob(image,(size_t) (q-pixels),pixels); 1163 if (image->previous == (Image *) NULL) 1164 if ((image->progress_monitor != (MagickProgressMonitor) NULL) && 1165 (QuantumTick(y,image->rows) != MagickFalse)) 1166 { 1167 status=image->progress_monitor(SaveImageTag,y,image->rows, 1168 image->client_data); 1169 if (status == MagickFalse) 1170 break; 1171 } 1172 } 1173 pixels=(unsigned char *) RelinquishMagickMemory(pixels); 1174 if (GetNextImageInList(image) == (Image *) NULL) 1175 break; 1176 image=SyncNextImageInList(image); 1177 status=SetImageProgress(image,SaveImagesTag,scene, 1178 GetImageListLength(image)); 1179 if (status == MagickFalse) 1180 break; 1181 scene++; 1182 } while (image_info->adjoin != MagickFalse); 1183 (void) CloseBlob(image); 1184 return(MagickTrue); 1185 }</code></pre> 1186 1187 <p>To invoke the custom coder from the command line, use these commands:</p> 1188 <pre class="highlight"><code>convert logo: logo.mgk 1189 display logo.mgk 1190 </code></pre> 1191 1192 <p>We provide the <a href="https://imagemagick.org/download/kits/">Magick Coder Kit</a> to help you get started writing your own custom coder.</p> 1193 1194 <h2><a class="anchor" id="filters"></a>Custom Image Filters</h2> 1195 1196 <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.html#process">-process</a> option or from the MagickCore API method <a href="api/module.html#ExecuteModuleProcess">ExecuteModuleProcess()</a>.</p> 1197 1198 <p>Here is a listing of a sample <a href="https://imagemagick.org/source/analyze.c">custom image filter</a>. It computes a few statistics such as the pixel brightness and saturation mean and standard-deviation.</p> 1199 <pre class="pre-scrollable"><code>#include <stdio.h> 1200 #include <stdlib.h> 1201 #include <string.h> 1202 #include <time.h> 1203 #include <assert.h> 1204 #include <math.h> 1205 #include <MagickCore/MagickCore.h> 1206 1208 /* 1209 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1210 % % 1211 % % 1212 % % 1213 % a n a l y z e I m a g e % 1214 % % 1215 % % 1216 % % 1217 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1218 % 1219 % analyzeImage() computes the brightness and saturation mean, standard 1220 % deviation, kurtosis and skewness and stores these values as attributes 1221 % of the image. 1222 % 1223 % The format of the analyzeImage method is: 1224 % 1225 % size_t analyzeImage(Image *images,const int argc,char **argv, 1226 % ExceptionInfo *exception) 1227 % 1228 % A description of each parameter follows: 1229 % 1230 % o image: the address of a structure of type Image. 1231 % 1232 % o argc: Specifies a pointer to an integer describing the number of 1233 % elements in the argument vector. 1234 % 1235 % o argv: Specifies a pointer to a text array containing the command line 1236 % arguments. 1237 % 1238 % o exception: return any errors or warnings in this structure. 1239 % 1240 */ 1241 1242 static void ConvertRGBToHSB(const double red,const double green, 1243 const double blue,double *hue,double *saturation,double *brightness) 1244 { 1245 double 1246 delta, 1247 max, 1248 min; 1249 1250 /* 1251 Convert RGB to HSB colorspace. 1252 */ 1253 assert(hue != (double *) NULL); 1254 assert(saturation != (double *) NULL); 1255 assert(brightness != (double *) NULL); 1256 *hue=0.0; 1257 *saturation=0.0; 1258 *brightness=0.0; 1259 min=red < green ? red : green; 1260 if (blue < min) 1261 min=blue; 1262 max=red > green ? red : green; 1263 if (blue > max) 1264 max=blue; 1265 if (fabs(max) < MagickEpsilon) 1266 return; 1267 delta=max-min; 1268 *saturation=delta/max; 1269 *brightness=QuantumScale*max; 1270 if (fabs(delta) < MagickEpsilon) 1271 return; 1272 if (fabs(red-max) < MagickEpsilon) 1273 *hue=(green-blue)/delta; 1274 else 1275 if (fabs(green-max) < MagickEpsilon) 1276 *hue=2.0+(blue-red)/delta; 1277 else 1278 *hue=4.0+(red-green)/delta; 1279 *hue/=6.0; 1280 if (*hue < 0.0) 1281 *hue+=1.0; 1282 } 1283 1284 ModuleExport size_t analyzeImage(Image **images,const int argc, 1285 const char **argv,ExceptionInfo *exception) 1286 { 1287 char 1288 text[MaxTextExtent]; 1289 1290 double 1291 area, 1292 brightness, 1293 brightness_mean, 1294 brightness_standard_deviation, 1295 brightness_kurtosis, 1296 brightness_skewness, 1297 brightness_sum_x, 1298 brightness_sum_x2, 1299 brightness_sum_x3, 1300 brightness_sum_x4, 1301 hue, 1302 saturation, 1303 saturation_mean, 1304 saturation_standard_deviation, 1305 saturation_kurtosis, 1306 saturation_skewness, 1307 saturation_sum_x, 1308 saturation_sum_x2, 1309 saturation_sum_x3, 1310 saturation_sum_x4; 1311 1312 Image 1313 *image; 1314 1315 assert(images != (Image **) NULL); 1316 assert(*images != (Image *) NULL); 1317 assert((*images)->signature == MagickCoreSignature); 1318 (void) argc; 1319 (void) argv; 1320 image=(*images); 1321 for ( ; image != (Image *) NULL; image=GetNextImageInList(image)) 1322 { 1323 CacheView 1324 *image_view; 1325 1326 long 1327 y; 1328 1329 MagickBooleanType 1330 status; 1331 1332 brightness_sum_x=0.0; 1333 brightness_sum_x2=0.0; 1334 brightness_sum_x3=0.0; 1335 brightness_sum_x4=0.0; 1336 brightness_mean=0.0; 1337 brightness_standard_deviation=0.0; 1338 brightness_kurtosis=0.0; 1339 brightness_skewness=0.0; 1340 saturation_sum_x=0.0; 1341 saturation_sum_x2=0.0; 1342 saturation_sum_x3=0.0; 1343 saturation_sum_x4=0.0; 1344 saturation_mean=0.0; 1345 saturation_standard_deviation=0.0; 1346 saturation_kurtosis=0.0; 1347 saturation_skewness=0.0; 1348 area=0.0; 1349 status=MagickTrue; 1350 image_view=AcquireVirtualCacheView(image,exception); 1351 for (y=0; y < (long) image->rows; y++) 1352 { 1353 register const Quantum 1354 *p; 1355 1356 register long 1357 x; 1358 1359 if (status == MagickFalse) 1360 continue; 1361 p=GetCacheViewVirtualPixels(image_view,0,y,image->columns,1,exception); 1362 if (p == (const Quantum *) NULL) 1363 { 1364 status=MagickFalse; 1365 continue; 1366 } 1367 for (x=0; x < (long) image->columns; x++) 1368 { 1369 ConvertRGBToHSB(GetPixelRed(image,p),GetPixelGreen(image,p), 1370 GetPixelBlue(image,p),&hue,&saturation,&brightness); 1371 brightness*=QuantumRange; 1372 brightness_sum_x+=brightness; 1373 brightness_sum_x2+=brightness*brightness; 1374 brightness_sum_x3+=brightness*brightness*brightness; 1375 brightness_sum_x4+=brightness*brightness*brightness*brightness; 1376 saturation*=QuantumRange; 1377 saturation_sum_x+=saturation; 1378 saturation_sum_x2+=saturation*saturation; 1379 saturation_sum_x3+=saturation*saturation*saturation; 1380 saturation_sum_x4+=saturation*saturation*saturation*saturation; 1381 area++; 1382 p+=GetPixelChannels(image); 1383 } 1384 } 1385 image_view=DestroyCacheView(image_view); 1386 if (area <= 0.0) 1387 break; 1388 brightness_mean=brightness_sum_x/area; 1389 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_mean); 1390 (void) SetImageProperty(image,"filter:brightness:mean",text,exception); 1391 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/ 1392 area*brightness_sum_x/area)); 1393 (void) FormatLocaleString(text,MaxTextExtent,"%g", 1394 brightness_standard_deviation); 1395 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text, 1396 exception); 1397 if (brightness_standard_deviation != 0) 1398 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean* 1399 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean* 1400 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean* 1401 brightness_mean*brightness_mean)/(brightness_standard_deviation* 1402 brightness_standard_deviation*brightness_standard_deviation* 1403 brightness_standard_deviation)-3.0; 1404 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_kurtosis); 1405 (void) SetImageProperty(image,"filter:brightness:kurtosis",text, 1406 exception); 1407 if (brightness_standard_deviation != 0) 1408 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean* 1409 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean* 1410 brightness_mean)/(brightness_standard_deviation* 1411 brightness_standard_deviation*brightness_standard_deviation); 1412 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_skewness); 1413 (void) SetImageProperty(image,"filter:brightness:skewness",text,exception); 1414 saturation_mean=saturation_sum_x/area; 1415 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_mean); 1416 (void) SetImageProperty(image,"filter:saturation:mean",text,exception); 1417 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/ 1418 area*saturation_sum_x/area)); 1419 (void) FormatLocaleString(text,MaxTextExtent,"%g", 1420 saturation_standard_deviation); 1421 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text, 1422 exception); 1423 if (saturation_standard_deviation != 0) 1424 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean* 1425 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean* 1426 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean* 1427 saturation_mean*saturation_mean)/(saturation_standard_deviation* 1428 saturation_standard_deviation*saturation_standard_deviation* 1429 saturation_standard_deviation)-3.0; 1430 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_kurtosis); 1431 (void) SetImageProperty(image,"filter:saturation:kurtosis",text,exception); 1432 if (saturation_standard_deviation != 0) 1433 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean* 1434 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean* 1435 saturation_mean)/(saturation_standard_deviation* 1436 saturation_standard_deviation*saturation_standard_deviation); 1437 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_skewness); 1438 (void) SetImageProperty(image,"filter:saturation:skewness",text,exception); 1439 } 1440 return(MagickImageFilterSignature); 1441 } 1442 </code></pre> 1443 1444 <p>To invoke the custom filter from the command line, use this command:</p> 1445 1446 <pre class="highlight"><code>convert logo: -process \"analyze\" -verbose info: 1447 Image: logo: 1448 Format: LOGO (ImageMagick Logo) 1449 Class: PseudoClass 1450 Geometry: 640x480 1451 ... 1452 filter:brightness:kurtosis: 8.17947 1453 filter:brightness:mean: 60632.1 1454 filter:brightness:skewness: -2.97118 1455 filter:brightness:standard-deviation: 13742.1 1456 filter:saturation:kurtosis: 4.33554 1457 filter:saturation:mean: 5951.55 1458 filter:saturation:skewness: 2.42848 1459 filter:saturation:standard-deviation: 15575.9 1460 </code></pre> 1461 1462 1463 <p>We provide the <a href="https://imagemagick.org/download/kits/">Magick Filter Kit</a> to help you get started writing your own custom image filter.</p> 1464 1465 </div> 1466 </div> 1467 </main><!-- /.container --> 1468 <footer class="magick-footer"> 1469 <p><a href="security-policy.html">Security</a> 1470 <a href="architecture.html">Architecture</a> 1471 <a href="links.html">Related</a> 1472 <a href="sitemap.html">Sitemap</a> 1473 1474 <a href="architecture.html#"><img class="d-inline" id="wand" alt="And Now a Touch of Magick" width="16" height="16" src="../images/wand.ico"/></a> 1475 1476 <a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> 1477 <a href="support.html">Donate</a> 1478 <a href="https://imagemagick.org/script/contact.php">Contact Us</a> 1479 <br/> 1480 <small> 1999-2019 ImageMagick Studio LLC</small></p> 1481 </footer> 1482 1483 <!-- Javascript assets --> 1484 <script src="assets/magick.js" crossorigin="anonymous"></script> 1485 <script>window.jQuery || document.write('<script src="https://localhost/ajax/libs/jquery/3.3.1/jquery.min.js"><\/script>')</script> 1486 </body> 1487 </html> 1488 <!-- Magick Cache 5th January 2019 11:42 -->
