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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); 140if (SetImageExtent(image,640,480) == MagickFalse) 141 { /* an exception was thrown */ } 142(void) QueryMagickColor("red",&image->background_color,&image->exception); 143SetImageBackgroundColor(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"): 148image=ReadImage(image_info,exception); 149if (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); 154if (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 181Quantum 182 *q; 183 184ssize_t 185 x, 186 y; 187 188destination=CloneImage(source,source->columns,source->rows,MagickTrue, 189 exception); 190if (destination == (Image *) NULL) 191 { /* an exception was thrown */ } 192for (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} 210if (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 221for (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} 229if (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 308Resource 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: 3462016-12-17T13:33:42-05:00 0:00.000 0.000u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 347 destroy 3482016-12-17T13:33:42-05:00 0:00.000 0.000u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 349 open LOGO[0] (Heap Memory, 640x480x4 4.688MiB) 3502016-12-17T13:33:42-05:00 0:00.010 0.000u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 351 open LOGO[0] (Heap Memory, 640x480x3 3.516MiB) 3522016-12-17T13:33:42-05:00 0:00.010 0.000u 7.0.0 Cache convert: cache.c/ClonePixelCachePixels/1044/Cache 353 Memory => Memory 3542016-12-17T13:33:42-05:00 0:00.020 0.010u 7.0.0 Cache convert: cache.c/ClonePixelCachePixels/1044/Cache 355 Memory => Memory 3562016-12-17T13:33:42-05:00 0:00.020 0.010u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 357 open LOGO[0] (Heap Memory, 640x480x3 3.516MiB) 3582016-12-17T13:33:42-05:00 0:00.050 0.100u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 359 destroy LOGO[0] 3602016-12-17T13:33:42-05:00 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 369convert -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 379view_1=AcquireVirtualCacheView(source,exception); 380view_2=AcquireVirtualCacheView(source,exception); 381for (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} 392view_2=DestroyCacheView(view_2); 393view_1=DestroyCacheView(view_1); 394if (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 431convert image.mpc -crop 100x100+0+0 +repage 1.png 432convert image.mpc -crop 100x100+100+0 +repage 2.png 433convert 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 */ 463image_info->client_data=(void *) MyData; 464image=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"); 480comment=GetImageProperty(image,"comment"); 481if (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 491profile=AcquireStringInfo(length); 492SetStringInfoDatum(profile,my_exif_profile); 493(void) SetImageProfile(image,"EXIF",profile); 494DestroyStringInfo(profile); 495profile=GetImageProfile(image,"EXIF"); 496if (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 526convert -distribute-cache 6668 & // start on 192.168.100.51 527convert -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 541MagickBooleanType 542 status; 543 544ssize_t 545 y; 546 547status=MagickTrue; 548image_view=AcquireVirtualCacheView(image,exception); 549#pragma omp parallel for schedule(static,4) shared(status) 550for (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} 583image_view=DestroyCacheView(image_view); 584if (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 593void 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: 662Performance[1]: 10i 1.135ips 1.000e 8.760u 0:08.810 663Performance[2]: 10i 2.020ips 0.640e 9.190u 0:04.950 664Performance[3]: 10i 2.786ips 0.710e 9.400u 0:03.590 665Performance[4]: 10i 3.378ips 0.749e 9.580u 0:02.960 666Performance[5]: 10i 4.032ips 0.780e 9.580u 0:02.480 667Performance[6]: 10i 4.566ips 0.801e 9.640u 0:02.190 668Performance[7]: 10i 3.788ips 0.769e 10.980u 0:02.640 669Performance[8]: 10i 4.115ips 0.784e 12.030u 0:02.430 670Performance[9]: 10i 4.484ips 0.798e 12.860u 0:02.230 671Performance[10]: 10i 4.274ips 0.790e 14.830u 0:02.340 672Performance[11]: 10i 4.348ips 0.793e 16.500u 0:02.300 673Performance[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 683Features: 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 703static 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" 779 780/* 781 Forward declarations. 782*/ 783static MagickBooleanType 784 WriteMGKImage(const ImageInfo *,Image *,ExceptionInfo *); 785 786/* 787%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 788% % 789% % 790% % 791% I s M G K % 792% % 793% % 794% % 795%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 796% 797% IsMGK() returns MagickTrue if the image format type, identified by the 798% magick string, is MGK. 799% 800% The format of the IsMGK method is: 801% 802% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length) 803% 804% A description of each parameter follows: 805% 806% o magick: This string is generally the first few bytes of an image file 807% or blob. 808% 809% o length: Specifies the length of the magick string. 810% 811*/ 812static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length) 813{ 814 if (length < 7) 815 return(MagickFalse); 816 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0) 817 return(MagickTrue); 818 return(MagickFalse); 819} 820 821/* 822%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 823% % 824% % 825% % 826% R e a d M G K I m a g e % 827% % 828% % 829% % 830%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 831% 832% ReadMGKImage() reads a MGK image file and returns it. It allocates the 833% memory necessary for the new Image structure and returns a pointer to the 834% new image. 835% 836% The format of the ReadMGKImage method is: 837% 838% Image *ReadMGKImage(const ImageInfo *image_info, 839% ExceptionInfo *exception) 840% 841% A description of each parameter follows: 842% 843% o image_info: the image info. 844% 845% o exception: return any errors or warnings in this structure. 846% 847*/ 848static Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception) 849{ 850 char 851 buffer[MaxTextExtent]; 852 853 Image 854 *image; 855 856 long 857 y; 858 859 MagickBooleanType 860 status; 861 862 register long 863 x; 864 865 register Quantum 866 *q; 867 868 register unsigned char 869 *p; 870 871 ssize_t 872 count; 873 874 unsigned char 875 *pixels; 876 877 unsigned long 878 columns, 879 rows; 880 881 /* 882 Open image file. 883 */ 884 assert(image_info != (const ImageInfo *) NULL); 885 assert(image_info->signature == MagickCoreSignature); 886 if (image_info->debug != MagickFalse) 887 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s", 888 image_info->filename); 889 assert(exception != (ExceptionInfo *) NULL); 890 assert(exception->signature == MagickCoreSignature); 891 image=AcquireImage(image_info,exception); 892 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception); 893 if (status == MagickFalse) 894 { 895 image=DestroyImageList(image); 896 return((Image *) NULL); 897 } 898 /* 899 Read MGK image. 900 */ 901 (void) ReadBlobString(image,buffer); /* read magic number */ 902 if (IsMGK(buffer,7) == MagickFalse) 903 ThrowReaderException(CorruptImageError,"ImproperImageHeader"); 904 (void) ReadBlobString(image,buffer); 905 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows); 906 if (count <= 0) 907 ThrowReaderException(CorruptImageError,"ImproperImageHeader"); 908 do 909 { 910 /* 911 Initialize image structure. 912 */ 913 image->columns=columns; 914 image->rows=rows; 915 image->depth=8; 916 if ((image_info->ping != MagickFalse) && (image_info->number_scenes != 0)) 917 if (image->scene >= (image_info->scene+image_info->number_scenes-1)) 918 break; 919 /* 920 Convert MGK raster image to pixel packets. 921 */ 922 if (SetImageExtent(image,image->columns,image->rows,exception) == MagickFalse) 923 return(DestroyImageList(image)); 924 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns, 925 3UL*sizeof(*pixels)); 926 if (pixels == (unsigned char *) NULL) 927 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed"); 928 for (y=0; y < (long) image->rows; y++) 929 { 930 count=(ssize_t) ReadBlob(image,(size_t) (3*image->columns),pixels); 931 if (count != (ssize_t) (3*image->columns)) 932 ThrowReaderException(CorruptImageError,"UnableToReadImageData"); 933 p=pixels; 934 q=QueueAuthenticPixels(image,0,y,image->columns,1,exception); 935 if (q == (Quantum *) NULL) 936 break; 937 for (x=0; x < (long) image->columns; x++) 938 { 939 SetPixelRed(image,ScaleCharToQuantum(*p++),q); 940 SetPixelGreen(image,ScaleCharToQuantum(*p++),q); 941 SetPixelBlue(image,ScaleCharToQuantum(*p++),q); 942 q+=GetPixelChannels(image); 943 } 944 if (SyncAuthenticPixels(image,exception) == MagickFalse) 945 break; 946 if (image->previous == (Image *) NULL) 947 if ((image->progress_monitor != (MagickProgressMonitor) NULL) && 948 (QuantumTick(y,image->rows) != MagickFalse)) 949 { 950 status=image->progress_monitor(LoadImageTag,y,image->rows, 951 image->client_data); 952 if (status == MagickFalse) 953 break; 954 } 955 } 956 pixels=(unsigned char *) RelinquishMagickMemory(pixels); 957 if (EOFBlob(image) != MagickFalse) 958 { 959 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile", 960 image->filename); 961 break; 962 } 963 /* 964 Proceed to next image. 965 */ 966 if (image_info->number_scenes != 0) 967 if (image->scene >= (image_info->scene+image_info->number_scenes-1)) 968 break; 969 *buffer='\0'; 970 (void) ReadBlobString(image,buffer); 971 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows); 972 if (count > 0) 973 { 974 /* 975 Allocate next image structure. 976 */ 977 AcquireNextImage(image_info,image,exception); 978 if (GetNextImageInList(image) == (Image *) NULL) 979 { 980 image=DestroyImageList(image); 981 return((Image *) NULL); 982 } 983 image=SyncNextImageInList(image); 984 if (image->progress_monitor != (MagickProgressMonitor) NULL) 985 { 986 status=SetImageProgress(image,LoadImageTag,TellBlob(image), 987 GetBlobSize(image)); 988 if (status == MagickFalse) 989 break; 990 } 991 } 992 } while (count > 0); 993 (void) CloseBlob(image); 994 return(GetFirstImageInList(image)); 995} 996 997/* 998%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 999% % 1000% % 1001% % 1002% R e g i s t e r M G K I m a g e % 1003% % 1004% % 1005% % 1006%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1007% 1008% RegisterMGKImage() adds attributes for the MGK image format to 1009% the list of supported formats. The attributes include the image format 1010% tag, a method to read and/or write the format, whether the format 1011% supports the saving of more than one frame to the same file or blob, 1012% whether the format supports native in-memory I/O, and a brief 1013% description of the format. 1014% 1015% The format of the RegisterMGKImage method is: 1016% 1017% unsigned long RegisterMGKImage(void) 1018% 1019*/ 1020ModuleExport unsigned long RegisterMGKImage(void) 1021{ 1022 MagickInfo 1023 *entry; 1024 1025 entry=AcquireMagickInfo("MGK","MGK","MGK image"); 1026 entry->decoder=(DecodeImageHandler *) ReadMGKImage; 1027 entry->encoder=(EncodeImageHandler *) WriteMGKImage; 1028 entry->magick=(IsImageFormatHandler *) IsMGK; 1029 (void) RegisterMagickInfo(entry); 1030 return(MagickImageCoderSignature); 1031} 1032 1033/* 1034%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1035% % 1036% % 1037% % 1038% U n r e g i s t e r M G K I m a g e % 1039% % 1040% % 1041% % 1042%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1043% 1044% UnregisterMGKImage() removes format registrations made by the 1045% MGK module from the list of supported formats. 1046% 1047% The format of the UnregisterMGKImage method is: 1048% 1049% UnregisterMGKImage(void) 1050% 1051*/ 1052ModuleExport void UnregisterMGKImage(void) 1053{ 1054 (void) UnregisterMagickInfo("MGK"); 1055} 1056 1057/* 1058%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1059% % 1060% % 1061% % 1062% W r i t e M G K I m a g e % 1063% % 1064% % 1065% % 1066%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1067% 1068% WriteMGKImage() writes an image to a file in red, green, and blue MGK 1069% rasterfile format. 1070% 1071% The format of the WriteMGKImage method is: 1072% 1073% MagickBooleanType WriteMGKImage(const ImageInfo *image_info, 1074% Image *image) 1075% 1076% A description of each parameter follows. 1077% 1078% o image_info: the image info. 1079% 1080% o image: The image. 1081% 1082% o exception: return any errors or warnings in this structure. 1083% 1084*/ 1085static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image, 1086 ExceptionInfo *exception) 1087{ 1088 char 1089 buffer[MaxTextExtent]; 1090 1091 long 1092 y; 1093 1094 MagickBooleanType 1095 status; 1096 1097 MagickOffsetType 1098 scene; 1099 1100 register const Quantum 1101 *p; 1102 1103 register long 1104 x; 1105 1106 register unsigned char 1107 *q; 1108 1109 unsigned char 1110 *pixels; 1111 1112 /* 1113 Open output image file. 1114 */ 1115 assert(image_info != (const ImageInfo *) NULL); 1116 assert(image_info->signature == MagickCoreSignature); 1117 assert(image != (Image *) NULL); 1118 assert(image->signature == MagickCoreSignature); 1119 if (image->debug != MagickFalse) 1120 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename); 1121 status=OpenBlob(image_info,image,WriteBinaryBlobMode,exception); 1122 if (status == MagickFalse) 1123 return(status); 1124 scene=0; 1125 do 1126 { 1127 /* 1128 Allocate memory for pixels. 1129 */ 1130 if (image->colorspace != RGBColorspace) 1131 (void) SetImageColorspace(image,RGBColorspace,exception); 1132 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns, 1133 3UL*sizeof(*pixels)); 1134 if (pixels == (unsigned char *) NULL) 1135 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed"); 1136 /* 1137 Initialize raster file header. 1138 */ 1139 (void) WriteBlobString(image,"id=mgk\n"); 1140 (void) FormatLocaleString(buffer,MaxTextExtent,"%lu %lu\n",image->columns, 1141 image->rows); 1142 (void) WriteBlobString(image,buffer); 1143 for (y=0; y < (long) image->rows; y++) 1144 { 1145 p=GetVirtualPixels(image,0,y,image->columns,1,exception); 1146 if (p == (const Quantum *) NULL) 1147 break; 1148 q=pixels; 1149 for (x=0; x < (long) image->columns; x++) 1150 { 1151 *q++=ScaleQuantumToChar(GetPixelRed(image,p)); 1152 *q++=ScaleQuantumToChar(GetPixelGreen(image,p)); 1153 *q++=ScaleQuantumToChar(GetPixelBlue(image,p)); 1154 p+=GetPixelChannels(image); 1155 } 1156 (void) WriteBlob(image,(size_t) (q-pixels),pixels); 1157 if (image->previous == (Image *) NULL) 1158 if ((image->progress_monitor != (MagickProgressMonitor) NULL) && 1159 (QuantumTick(y,image->rows) != MagickFalse)) 1160 { 1161 status=image->progress_monitor(SaveImageTag,y,image->rows, 1162 image->client_data); 1163 if (status == MagickFalse) 1164 break; 1165 } 1166 } 1167 pixels=(unsigned char *) RelinquishMagickMemory(pixels); 1168 if (GetNextImageInList(image) == (Image *) NULL) 1169 break; 1170 image=SyncNextImageInList(image); 1171 status=SetImageProgress(image,SaveImagesTag,scene, 1172 GetImageListLength(image)); 1173 if (status == MagickFalse) 1174 break; 1175 scene++; 1176 } while (image_info->adjoin != MagickFalse); 1177 (void) CloseBlob(image); 1178 return(MagickTrue); 1179}</code></pre> 1180 1181<p>To invoke the custom coder from the command line, use these commands:</p> 1182<pre class="highlight"><code>convert logo: logo.mgk 1183display logo.mgk 1184</code></pre> 1185 1186<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> 1187 1188<h2><a class="anchor" id="filters"></a>Custom Image Filters</h2> 1189 1190<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> 1191 1192<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> 1193<pre class="pre-scrollable"><code>#include <stdio.h> 1194#include <stdlib.h> 1195#include <string.h> 1196#include <time.h> 1197#include <assert.h> 1198#include <math.h> 1199#include <MagickCore/MagickCore.h> 1200 1201/* 1202%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1203% % 1204% % 1205% % 1206% a n a l y z e I m a g e % 1207% % 1208% % 1209% % 1210%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1211% 1212% analyzeImage() computes the brightness and saturation mean, standard 1213% deviation, kurtosis and skewness and stores these values as attributes 1214% of the image. 1215% 1216% The format of the analyzeImage method is: 1217% 1218% size_t analyzeImage(Image *images,const int argc,char **argv, 1219% ExceptionInfo *exception) 1220% 1221% A description of each parameter follows: 1222% 1223% o image: the address of a structure of type Image. 1224% 1225% o argc: Specifies a pointer to an integer describing the number of 1226% elements in the argument vector. 1227% 1228% o argv: Specifies a pointer to a text array containing the command line 1229% arguments. 1230% 1231% o exception: return any errors or warnings in this structure. 1232% 1233*/ 1234 1235static void ConvertRGBToHSB(const double red,const double green, 1236 const double blue,double *hue,double *saturation,double *brightness) 1237{ 1238 double 1239 delta, 1240 max, 1241 min; 1242 1243 /* 1244 Convert RGB to HSB colorspace. 1245 */ 1246 assert(hue != (double *) NULL); 1247 assert(saturation != (double *) NULL); 1248 assert(brightness != (double *) NULL); 1249 *hue=0.0; 1250 *saturation=0.0; 1251 *brightness=0.0; 1252 min=red < green ? red : green; 1253 if (blue < min) 1254 min=blue; 1255 max=red > green ? red : green; 1256 if (blue > max) 1257 max=blue; 1258 if (fabs(max) < MagickEpsilon) 1259 return; 1260 delta=max-min; 1261 *saturation=delta/max; 1262 *brightness=QuantumScale*max; 1263 if (fabs(delta) < MagickEpsilon) 1264 return; 1265 if (fabs(red-max) < MagickEpsilon) 1266 *hue=(green-blue)/delta; 1267 else 1268 if (fabs(green-max) < MagickEpsilon) 1269 *hue=2.0+(blue-red)/delta; 1270 else 1271 *hue=4.0+(red-green)/delta; 1272 *hue/=6.0; 1273 if (*hue < 0.0) 1274 *hue+=1.0; 1275} 1276 1277ModuleExport size_t analyzeImage(Image **images,const int argc, 1278 const char **argv,ExceptionInfo *exception) 1279{ 1280 char 1281 text[MaxTextExtent]; 1282 1283 double 1284 area, 1285 brightness, 1286 brightness_mean, 1287 brightness_standard_deviation, 1288 brightness_kurtosis, 1289 brightness_skewness, 1290 brightness_sum_x, 1291 brightness_sum_x2, 1292 brightness_sum_x3, 1293 brightness_sum_x4, 1294 hue, 1295 saturation, 1296 saturation_mean, 1297 saturation_standard_deviation, 1298 saturation_kurtosis, 1299 saturation_skewness, 1300 saturation_sum_x, 1301 saturation_sum_x2, 1302 saturation_sum_x3, 1303 saturation_sum_x4; 1304 1305 Image 1306 *image; 1307 1308 assert(images != (Image **) NULL); 1309 assert(*images != (Image *) NULL); 1310 assert((*images)->signature == MagickCoreSignature); 1311 (void) argc; 1312 (void) argv; 1313 image=(*images); 1314 for ( ; image != (Image *) NULL; image=GetNextImageInList(image)) 1315 { 1316 CacheView 1317 *image_view; 1318 1319 long 1320 y; 1321 1322 MagickBooleanType 1323 status; 1324 1325 brightness_sum_x=0.0; 1326 brightness_sum_x2=0.0; 1327 brightness_sum_x3=0.0; 1328 brightness_sum_x4=0.0; 1329 brightness_mean=0.0; 1330 brightness_standard_deviation=0.0; 1331 brightness_kurtosis=0.0; 1332 brightness_skewness=0.0; 1333 saturation_sum_x=0.0; 1334 saturation_sum_x2=0.0; 1335 saturation_sum_x3=0.0; 1336 saturation_sum_x4=0.0; 1337 saturation_mean=0.0; 1338 saturation_standard_deviation=0.0; 1339 saturation_kurtosis=0.0; 1340 saturation_skewness=0.0; 1341 area=0.0; 1342 status=MagickTrue; 1343 image_view=AcquireVirtualCacheView(image,exception); 1344 for (y=0; y < (long) image->rows; y++) 1345 { 1346 register const Quantum 1347 *p; 1348 1349 register long 1350 x; 1351 1352 if (status == MagickFalse) 1353 continue; 1354 p=GetCacheViewVirtualPixels(image_view,0,y,image->columns,1,exception); 1355 if (p == (const Quantum *) NULL) 1356 { 1357 status=MagickFalse; 1358 continue; 1359 } 1360 for (x=0; x < (long) image->columns; x++) 1361 { 1362 ConvertRGBToHSB(GetPixelRed(image,p),GetPixelGreen(image,p), 1363 GetPixelBlue(image,p),&hue,&saturation,&brightness); 1364 brightness*=QuantumRange; 1365 brightness_sum_x+=brightness; 1366 brightness_sum_x2+=brightness*brightness; 1367 brightness_sum_x3+=brightness*brightness*brightness; 1368 brightness_sum_x4+=brightness*brightness*brightness*brightness; 1369 saturation*=QuantumRange; 1370 saturation_sum_x+=saturation; 1371 saturation_sum_x2+=saturation*saturation; 1372 saturation_sum_x3+=saturation*saturation*saturation; 1373 saturation_sum_x4+=saturation*saturation*saturation*saturation; 1374 area++; 1375 p+=GetPixelChannels(image); 1376 } 1377 } 1378 image_view=DestroyCacheView(image_view); 1379 if (area <= 0.0) 1380 break; 1381 brightness_mean=brightness_sum_x/area; 1382 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_mean); 1383 (void) SetImageProperty(image,"filter:brightness:mean",text,exception); 1384 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/ 1385 area*brightness_sum_x/area)); 1386 (void) FormatLocaleString(text,MaxTextExtent,"%g", 1387 brightness_standard_deviation); 1388 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text, 1389 exception); 1390 if (brightness_standard_deviation != 0) 1391 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean* 1392 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean* 1393 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean* 1394 brightness_mean*brightness_mean)/(brightness_standard_deviation* 1395 brightness_standard_deviation*brightness_standard_deviation* 1396 brightness_standard_deviation)-3.0; 1397 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_kurtosis); 1398 (void) SetImageProperty(image,"filter:brightness:kurtosis",text, 1399 exception); 1400 if (brightness_standard_deviation != 0) 1401 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean* 1402 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean* 1403 brightness_mean)/(brightness_standard_deviation* 1404 brightness_standard_deviation*brightness_standard_deviation); 1405 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_skewness); 1406 (void) SetImageProperty(image,"filter:brightness:skewness",text,exception); 1407 saturation_mean=saturation_sum_x/area; 1408 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_mean); 1409 (void) SetImageProperty(image,"filter:saturation:mean",text,exception); 1410 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/ 1411 area*saturation_sum_x/area)); 1412 (void) FormatLocaleString(text,MaxTextExtent,"%g", 1413 saturation_standard_deviation); 1414 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text, 1415 exception); 1416 if (saturation_standard_deviation != 0) 1417 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean* 1418 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean* 1419 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean* 1420 saturation_mean*saturation_mean)/(saturation_standard_deviation* 1421 saturation_standard_deviation*saturation_standard_deviation* 1422 saturation_standard_deviation)-3.0; 1423 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_kurtosis); 1424 (void) SetImageProperty(image,"filter:saturation:kurtosis",text,exception); 1425 if (saturation_standard_deviation != 0) 1426 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean* 1427 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean* 1428 saturation_mean)/(saturation_standard_deviation* 1429 saturation_standard_deviation*saturation_standard_deviation); 1430 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_skewness); 1431 (void) SetImageProperty(image,"filter:saturation:skewness",text,exception); 1432 } 1433 return(MagickImageFilterSignature); 1434} 1435</code></pre> 1436 1437<p>To invoke the custom filter from the command line, use this command:</p> 1438 1439<pre class="highlight"><code>convert logo: -process \"analyze\" -verbose info: 1440 Image: logo: 1441 Format: LOGO (ImageMagick Logo) 1442 Class: PseudoClass 1443 Geometry: 640x480 1444 ... 1445 filter:brightness:kurtosis: 8.17947 1446 filter:brightness:mean: 60632.1 1447 filter:brightness:skewness: -2.97118 1448 filter:brightness:standard-deviation: 13742.1 1449 filter:saturation:kurtosis: 4.33554 1450 filter:saturation:mean: 5951.55 1451 filter:saturation:skewness: 2.42848 1452 filter:saturation:standard-deviation: 15575.9 1453</code></pre> 1454 1455 1456<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> 1457 1458</div> 1459 </div> 1460 </main><!-- /.container --> 1461 <footer class="magick-footer"> 1462 <p><a href="security-policy.html">Security</a> • 1463 <a href="architecture.html">Architecture</a> • 1464 <a href="links.html">Related</a> • 1465 <a href="sitemap.html">Sitemap</a> 1466 1467 <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> 1468 1469 <a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> • 1470 <a href="support.html">Donate</a> • 1471 <a href="https://imagemagick.org/script/contact.php">Contact Us</a> 1472 <br/> 1473 <small>© 1999-2019 ImageMagick Studio LLC</small></p> 1474 </footer> 1475 1476 <!-- Javascript assets --> 1477 <script src="assets/magick.js" crossorigin="anonymous"></script> 1478 <script>window.jQuery || document.write('<script src="https://localhost/ajax/libs/jquery/3.3.1/jquery.min.js"><\/script>')</script> 1479</body> 1480</html> 1481<!-- Magick Cache 5th January 2019 11:42 -->
