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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> 93 94<h2><a class="anchor" id="overview"></a>Architecture Overview</h2> 95 96<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> 97 98<ul> 99 <li>colorspace (e.g sRGB, linear RGB, linear GRAY, CMYK, YUV, Lab, etc.)</li> 100 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li> 101 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li> 102 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li> 103 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li> 104 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li> 105</ul> 106 107<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> 108 109<p>An efficient implementation of an image processing algorithm may require we get or set:</p> 110 111<ul> 112 <li>one pixel a time (e.g. pixel at location 10,3)</li> 113 <li>a single scanline (e.g. all pixels from row 4)</li> 114 <li>a few scanlines at once (e.g. pixel rows 4-7)</li> 115 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li> 116 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li> 117 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li> 118 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li> 119 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li> 120 <li>a pixel component that is unsigned (65311) or in a floating-point representation (e.g. 0.17836)</li> 121 <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> 122 <li>one or more pixels simultaneously in different threads of execution</li> 123 <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> 124 <li>traits associated with each channel to specify whether the pixel channel is copied, updated, or blended</li> 125 <li>masks that define which pixels are eligible to be updated</li> 126 <li>extra channels that benefits the user but otherwise remain untouched by ImageMagick image processing algorithms</li> 127</ul> 128 129<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> 130 131<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> 132 133<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> 134 135<h2><a class="anchor" id="cache"></a>The Pixel Cache</h2> 136 137<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> 138 139<h3>Create the Pixel Cache</h3> 140 141<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> 142 143<dl> 144<dt class="col-md-8">Create an image canvas initialized to the background color:</dt><br/> 145<dd class="col-md-8"><pre class="highlight"><code>image=AllocateImage(image_info); 146if (SetImageExtent(image,640,480) == MagickFalse) 147 { /* an exception was thrown */ } 148(void) QueryMagickColor("red",&image->background_color,&image->exception); 149SetImageBackgroundColor(image); 150</code></pre></dd> 151 152<dt class="col-md-8">Create an image from a JPEG image on disk:</dt><br/> 153<dd class="col-md-8"><pre class="highlight"><code>(void) strcpy(image_info->filename,"image.jpg"): 154image=ReadImage(image_info,exception); 155if (image == (Image *) NULL) 156 { /* an exception was thrown */ } 157</code></pre></dd> 158<dt class="col-md-8">Create an image from a memory based image:</dt><br/> 159<dd class="col-md-8"><pre class="highlight"><code>image=BlobToImage(blob_info,blob,extent,exception); 160if (image == (Image *) NULL) 161 { /* an exception was thrown */ } 162</code></pre></dd> 163</dl> 164 165<p>In our discussion of the pixel cache, we use the <a href="magick-core.html">MagickCore API</a> to illustrate our points, however, the principles are the same for other program interfaces to ImageMagick.</p> 166 167<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> 168 169<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 7.0.9-14 2020-01-01 Q16 https://imagemagick.org</span></pre> 170<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> 171 172<h3><a class="anchor" id="authentic-pixels"></a>Access the Pixel Cache</h3> 173 174<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> 175<ul> 176 <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> 177 <li><a href="api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a>: gets pixels that you intend to modify</li> 178 <li><a href="api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a>: queue pixels that you intend to set</li> 179 <li><a href="api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a>: update the pixel cache with any modified pixels</li> 180</ul> 181 182<p>Here is a typical <a href="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> 183 184<pre class="pre-scrollable"><code>const Quantum 185 *p; 186 187Quantum 188 *q; 189 190ssize_t 191 x, 192 y; 193 194destination=CloneImage(source,source->columns,source->rows,MagickTrue, 195 exception); 196if (destination == (Image *) NULL) 197 { /* an exception was thrown */ } 198for (y=0; y < (ssize_t) source->rows; y++) 199{ 200 p=GetVirtualPixels(source,0,y,source->columns,1,exception); 201 q=GetAuthenticPixels(destination,0,y,destination->columns,1,exception); 202 if ((p == (const Quantum *) NULL) || (q == (Quantum *) NULL) 203 break; 204 for (x=0; x < (ssize_t) source->columns; x++) 205 { 206 SetPixelRed(image,90*p->red/100,q); 207 SetPixelGreen(image,90*p->green/100,q); 208 SetPixelBlue(image,90*p->blue/100,q); 209 SetPixelAlpha(image,90*p->opacity/100,q); 210 p+=GetPixelChannels(source); 211 q+=GetPixelChannels(destination); 212 } 213 if (SyncAuthenticPixels(destination,exception) == MagickFalse) 214 break; 215} 216if (y < (ssize_t) source->rows) 217 { /* an exception was thrown */ } 218</code></pre> 219 220<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> 221 222<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> 223 224<pre class="highlight"><code>const void 225 *metacontent; 226 227for (y=0; y < (ssize_t) source->rows; y++) 228{ 229 p=GetVirtualPixels(source,0,y,source->columns,1); 230 if (p == (const Quantum *) NULL) 231 break; 232 metacontent=GetVirtualMetacontent(source); 233 /* print meta content here */ 234} 235if (y < (ssize_t) source->rows) 236 /* an exception was thrown */ 237</code></pre> 238 239<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> 240 241<pre class="highlight"><code>p=GetVirtualPixels(source,-3,-3,source->columns+3,6,exception); 242</code></pre> 243 244<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p> 245 246<h3><a class="anchor" id="virtual-pixels"></a>Virtual Pixels</h3> 247 248<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> 249 <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> 250 251<dl class="row"> 252<dt class="col-md-4">background</dt> 253<dd class="col-md-8">the area surrounding the image is the background color</dd> 254<dt class="col-md-4">black</dt> 255<dd class="col-md-8">the area surrounding the image is black</dd> 256<dt class="col-md-4">checker-tile</dt> 257<dd class="col-md-8">alternate squares with image and background color</dd> 258<dt class="col-md-4">dither</dt> 259<dd class="col-md-8">non-random 32x32 dithered pattern</dd> 260<dt class="col-md-4">edge</dt> 261<dd class="col-md-8">extend the edge pixel toward infinity (default)</dd> 262<dt class="col-md-4">gray</dt> 263<dd class="col-md-8">the area surrounding the image is gray</dd> 264<dt class="col-md-4">horizontal-tile</dt> 265<dd class="col-md-8">horizontally tile the image, background color above/below</dd> 266<dt class="col-md-4">horizontal-tile-edge</dt> 267<dd class="col-md-8">horizontally tile the image and replicate the side edge pixels</dd> 268<dt class="col-md-4">mirror</dt> 269<dd class="col-md-8">mirror tile the image</dd> 270<dt class="col-md-4">random</dt> 271<dd class="col-md-8">choose a random pixel from the image</dd> 272<dt class="col-md-4">tile</dt> 273<dd class="col-md-8">tile the image</dd> 274<dt class="col-md-4">transparent</dt> 275<dd class="col-md-8">the area surrounding the image is transparent blackness</dd> 276<dt class="col-md-4">vertical-tile</dt> 277<dd class="col-md-8">vertically tile the image, sides are background color</dd> 278<dt class="col-md-4">vertical-tile-edge</dt> 279<dd class="col-md-8">vertically tile the image and replicate the side edge pixels</dd> 280<dt class="col-md-4">white</dt> 281<dd class="col-md-8">the area surrounding the image is white</dd> 282</dl> 283 284 285<h3>Cache Storage and Resource Requirements</h3> 286 287<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> 288 289<dl class="row"> 290 <dt class="col-md-4">width</dt> 291 <dd class="col-md-8">maximum width of an image. Exceed this limit and an exception is thrown and processing stops.</dd> 292 <dt class="col-md-4">height</dt> 293 <dd class="col-md-8">maximum height of an image. Exceed this limit and an exception is thrown and processing stops.</dd> 294 <dt class="col-md-4">area</dt> 295 <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> 296 <dt class="col-md-4">memory</dt> 297 <dd class="col-md-8">maximum amount of memory in bytes to allocate for the pixel cache from the heap.</dd> 298 <dt class="col-md-4">map</dt> 299 <dd class="col-md-8">maximum amount of memory map in bytes to allocate for the pixel cache.</dd> 300 <dt class="col-md-4">disk</dt> 301 <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> 302 <dt class="col-md-4">files</dt> 303 <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> 304 <dt class="col-md-4">thread</dt> 305 <dd class="col-md-8">maximum number of threads that are permitted to run in parallel.</dd> 306 <dt class="col-md-4">time</dt> 307 <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> 308</dl> 309 310<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> 311 312<p>To determine the current setting of these limits, use this command:</p> 313<pre class="highlight">-> identify -list resource 314Resource limits: 315 Width: 100MP 316 Height: 100MP 317 Area: 25.181GB 318 Memory: 11.726GiB 319 Map: 23.452GiB 320 Disk: unlimited 321 File: 768 322 Thread: 12 323 Throttle: 0 324 Time: unlimited 325</pre> 326 327<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> 328<pre class="highlight"><code><policymap> 329 <policy domain="resource" name="temporary-path" value="/tmp"/> 330 <policy domain="resource" name="memory" value="256MiB"/> 331 <policy domain="resource" name="map" value="512MiB"/> 332 <policy domain="resource" name="width" value="8KP"/> 333 <policy domain="resource" name="height" value="8KP"/> 334 <policy domain="resource" name="area" value="128MB"/> 335 <policy domain="resource" name="disk" value="1GiB"/> 336 <policy domain="resource" name="file" value="768"/> 337 <policy domain="resource" name="thread" value="2"/> 338 <policy domain="resource" name="throttle" value="0"/> 339 <policy domain="resource" name="time" value="120"/> 340 <policy domain="system" name="precision" value="6"/> 341 <policy domain="cache" name="shared-secret" value="replace with your secret phrase" stealth="true"/> 342 <policy domain="delegate" rights="none" pattern="HTTPS" /> 343 <policy domain="path" rights="none" pattern="@*"/> <!-- indirect reads not permitted --> 344</policymap> 345</code></pre> 346<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> 347 348<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> 349 350<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> 351<pre class="highlight">-> convert -debug cache logo: -sharpen 3x2 null: 3522016-12-17T13:33:42-05:00 0:00.000 0.000u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 353 destroy 3542016-12-17T13:33:42-05:00 0:00.000 0.000u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 355 open LOGO[0] (Heap Memory, 640x480x4 4.688MiB) 3562016-12-17T13:33:42-05:00 0:00.010 0.000u 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 0:00.010 0.000u 7.0.0 Cache convert: cache.c/ClonePixelCachePixels/1044/Cache 359 Memory => Memory 3602016-12-17T13:33:42-05:00 0:00.020 0.010u 7.0.0 Cache convert: cache.c/ClonePixelCachePixels/1044/Cache 361 Memory => Memory 3622016-12-17T13:33:42-05:00 0:00.020 0.010u 7.0.0 Cache convert: cache.c/OpenPixelCache/3834/Cache 363 open LOGO[0] (Heap Memory, 640x480x3 3.516MiB) 3642016-12-17T13:33:42-05:00 0:00.050 0.100u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 365 destroy LOGO[0] 3662016-12-17T13:33:42-05:00 0:00.050 0.100u 7.0.0 Cache convert: cache.c/DestroyPixelCache/1275/Cache 367 destroy LOGO[0] 368</pre> 369<p>This command utilizes a pixel cache in memory. The logo consumed 4.688MiB and after it was sharpened, 3.516MiB.</p> 370 371 372<h3>Distributed Pixel Cache</h3> 373<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> 374<pre class="highlight"><code>convert -distribute-cache 6668 & // start on 192.168.100.50 375convert -define registry:cache:hosts=192.168.100.50:6668 myimage.jpg -sharpen 5x2 mimage.png 376</code></pre> 377 378<h3>Cache Views</h3> 379 380<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> 381<pre class="pre-scrollable"><code>CacheView 382 *view_1, 383 *view_2; 384 385view_1=AcquireVirtualCacheView(source,exception); 386view_2=AcquireVirtualCacheView(source,exception); 387for (y=0; y < (ssize_t) source->rows; y++) 388{ 389 u=GetCacheViewVirtualPixels(view_1,0,y,source->columns,1,exception); 390 v=GetCacheViewVirtualPixels(view_2,0,source->rows-y-1,source->columns,1,exception); 391 if ((u == (const Quantum *) NULL) || (v == (const Quantum *) NULL)) 392 break; 393 for (x=0; x < (ssize_t) source->columns; x++) 394 { 395 /* do something with u & v here */ 396 } 397} 398view_2=DestroyCacheView(view_2); 399view_1=DestroyCacheView(view_1); 400if (y < (ssize_t) source->rows) 401 { /* an exception was thrown */ } 402</code></pre> 403 404<h3>Magick Persistent Cache Format</h3> 405 406<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> 407<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> 408 409<h3>Best Practices</h3> 410 411<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> 412 413<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> 414 415<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> 416 417<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> 418 419<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> 420 421<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> 422 423<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> 424 425<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> 426 427<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> 428 429<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> 430<pre class="highlight"><code>convert -limit memory 2GB -limit map 4GB -define registry:temporary-path=/data/tmp ... 431</code></pre> 432 433<p>Set global resource limits for your environment in the <code>policy.xml</code> configuration file.</p> 434 435<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> 436<pre class="highlight"><code>convert image.tif image.mpc 437convert image.mpc -crop 100x100+0+0 +repage 1.png 438convert image.mpc -crop 100x100+100+0 +repage 2.png 439convert image.mpc -crop 100x100+200+0 +repage 3.png 440</code></pre> 441 442<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> 443 444<h2><a class="anchor" id="stream"></a>Streaming Pixels</h2> 445 446<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> 447 448<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> 449<pre class="pre-scrollable"><code>static size_t StreamPixels(const Image *image,const void *pixels,const size_t columns) 450{ 451 register const Quantum 452 *p; 453 454 MyData 455 *my_data; 456 457 my_data=(MyData *) image->client_data; 458 p=(Quantum *) pixels; 459 if (p != (const Quantum *) NULL) 460 { 461 /* process pixels here */ 462 } 463 return(columns); 464} 465 466... 467 468/* invoke the pixel stream here */ 469image_info->client_data=(void *) MyData; 470image=ReadStream(image_info,&StreamPixels,exception); 471</code></pre> 472 473<p>We also provide a lightweight tool, <a href="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="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> 474 475<h2><a class="anchor" id="properties"></a>Image Properties and Profiles</h2> 476 477<p>Images have metadata associated with them in the form of properties (e.g. width, height, description, etc.) and profiles (e.g. EXIF, IPTC, color management). ImageMagick provides convenient methods to get, set, or update image properties and get, set, update, or apply profiles. Some of the more popular image properties are associated with the Image structure in the MagickCore API. For example:</p> 478<pre class="highlight"><code>(void) printf("image width: %lu, height: %lu\n",image->columns,image->rows); 479</code></pre> 480 481<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> 482<pre class="highlight"><code>const char 483 *comment; 484 485(void) SetImageProperty(image,"comment","This space for rent"); 486comment=GetImageProperty(image,"comment"); 487if (comment == (const char *) NULL) 488 (void) printf("Image comment: %s\n",comment); 489</code></pre> 490 491<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> 492 493<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> 494<pre class="highlight"><code>StringInfo 495 *profile; 496 497profile=AcquireStringInfo(length); 498SetStringInfoDatum(profile,my_exif_profile); 499(void) SetImageProfile(image,"EXIF",profile); 500DestroyStringInfo(profile); 501profile=GetImageProfile(image,"EXIF"); 502if (profile != (StringInfo *) NULL) 503 (void) PrintStringInfo(stdout,"EXIF",profile); 504</code></pre> 505 506<h2><a class="anchor" id="tera-pixel"></a>Large Image Support</h2> 507<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 (up to 2147483647 rows/columns) and up to 9 exa-pixels on a 64-bit OS (up to 9223372036854775807 rows/columns). 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> 508<pre class="highlight"><code>convert logo: -resize 250000x250000 logo.miff 509</code></pre> 510 511<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> 512<pre class="highlight"><code>convert -define registry:temporary-path=/data/tmp logo: \ <br/> -resize 250000x250000 logo.miff 513</code></pre> 514 515<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> 516<pre class="highlight"><code>convert -define registry:temporary-path=/data/tmp -limit memory 16mb \ 517 logo: -resize 250000x250000 logo.miff 518</code></pre> 519 520<p>Here we force all image pixels to disk:</p> 521<pre class="highlight"><code>convert -define registry:temporary-path=/data/tmp -limit area 0 \ 522 logo: -resize 250000x250000 logo.miff 523</code></pre> 524 525<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> 526<pre class="highlight"><code>convert -monitor -limit memory 2GiB -limit map 4GiB -define registry:temporary-path=/data/tmp \ 527 logo: -resize 250000x250000 logo.miff 528</code></pre> 529 530<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> 531<pre class="highlight"><code>convert -distribute-cache 6668 & // start on 192.168.100.50 532convert -distribute-cache 6668 & // start on 192.168.100.51 533convert -limit memory 2mb -limit map 2mb -limit disk 2gb \ 534 -define registry:cache:hosts=192.168.100.50:6668,192.168.100.51:6668 \ 535 myhugeimage.jpg -sharpen 5x2 myhugeimage.png 536</code></pre> 537<p>Due to network latency, expect a substantial slow-down in processing your workflow.</p> 538 539<h2><a class="anchor" id="threads"></a>Threads of Execution</h2> 540 541<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="magick-wand.html">MagickWand API</a>, are completely thread safe so there are no special precautions for threads of execution.</p> 542 543<p>Here is an MagickCore code snippet that takes advantage of threads of execution with the <a href="openmp.html">OpenMP</a> programming paradigm:</p> 544<pre class="pre-scrollable"><code>CacheView 545 *image_view; 546 547MagickBooleanType 548 status; 549 550ssize_t 551 y; 552 553status=MagickTrue; 554image_view=AcquireVirtualCacheView(image,exception); 555#pragma omp parallel for schedule(static,4) shared(status) 556for (y=0; y < (ssize_t) image->rows; y++) 557{ 558 register Quantum 559 *q; 560 561 register ssize_t 562 x; 563 564 register void 565 *metacontent; 566 567 if (status == MagickFalse) 568 continue; 569 q=GetCacheViewAuthenticPixels(image_view,0,y,image->columns,1,exception); 570 if (q == (Quantum *) NULL) 571 { 572 status=MagickFalse; 573 continue; 574 } 575 metacontent=GetCacheViewAuthenticMetacontent(image_view); 576 for (x=0; x < (ssize_t) image->columns; x++) 577 { 578 SetPixelRed(image,...,q); 579 SetPixelGreen(image,...,q); 580 SetPixelBlue(image,...,q); 581 SetPixelAlpha(image,...,q); 582 if (metacontent != NULL) 583 metacontent[indexes+x]=...; 584 q+=GetPixelChannels(image); 585 } 586 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse) 587 status=MagickFalse; 588} 589image_view=DestroyCacheView(image_view); 590if (status == MagickFalse) 591 perror("something went wrong"); 592</code></pre> 593 594<p>This code snippet converts an uncompressed Windows bitmap to a Magick++ image:</p> 595<pre class="pre-scrollable"><code>#include "Magick++.h" 596#include <assert.h> 597#include "omp.h" 598 599void ConvertBMPToImage(const BITMAPINFOHEADER *bmp_info, 600 const unsigned char *restrict pixels,Magick::Image *image) 601{ 602 /* 603 Prepare the image so that we can modify the pixels directly. 604 */ 605 assert(bmp_info->biCompression == BI_RGB); 606 assert(bmp_info->biWidth == image->columns()); 607 assert(abs(bmp_info->biHeight) == image->rows()); 608 image->modifyImage(); 609 if (bmp_info->biBitCount == 24) 610 image->type(MagickCore::TrueColorType); 611 else 612 image->type(MagickCore::TrueColorMatteType); 613 register unsigned int bytes_per_row=bmp_info->biWidth*bmp_info->biBitCount/8; 614 if (bytes_per_row % 4 != 0) { 615 bytes_per_row=bytes_per_row+(4-bytes_per_row % 4); // divisible by 4. 616 } 617 /* 618 Copy all pixel data, row by row. 619 */ 620 #pragma omp parallel for 621 for (int y=0; y < int(image->rows()); y++) 622 { 623 int 624 row; 625 626 register const unsigned char 627 *restrict p; 628 629 register MagickCore::Quantum 630 *restrict q; 631 632 row=(bmp_info->biHeight > 0) ? (image->rows()-y-1) : y; 633 p=pixels+row*bytes_per_row; 634 q=image->setPixels(0,y,image->columns(),1); 635 for (int x=0; x < int(image->columns()); x++) 636 { 637 SetPixelBlue(image,p[0],q); 638 SetPixelGreen(image,p[1],q); 639 SetPixelRed(image,p[2],q); 640 if (bmp_info->biBitCount == 32) { 641 SetPixelAlpha(image,p[3],q); 642 } 643 q+=GetPixelChannels(image); 644 p+=bmp_info->biBitCount/8; 645 } 646 image->syncPixels(); // sync pixels to pixel cache. 647 } 648 return; 649}</code></pre> 650 651<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> 652 653<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="magick-wand.html#wand-view">MagickWand</a> and <a href="magick-core.html#image-view">MagickCore</a>.</p> 654 655<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> 656<pre class="highlight"><code><policy domain="resource" name="thread" value="2"/> 657</code></pre> 658 659<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> 660<pre class="highlight"><code>export MAGICK_THREAD_LIMIT=12 661</code></pre> 662 663<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> 664 665<p>You can further increase performance by reducing lock contention with the <a href="http://goog-perftools.sourceforge.net/doc/tcmalloc.html">tcmalloc</a> memory allocation library. To enable, add <code>--with-tcmalloc</code> to the <code>configure</code> command-line when you build ImageMagick.</p> 666 667<h5>Threading Performance</h5> 668<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> 669<pre class="highlight">-> convert -bench 10 model.png -sharpen 5x2 null: 670Performance[1]: 10i 1.135ips 1.000e 8.760u 0:08.810 671Performance[2]: 10i 2.020ips 0.640e 9.190u 0:04.950 672Performance[3]: 10i 2.786ips 0.710e 9.400u 0:03.590 673Performance[4]: 10i 3.378ips 0.749e 9.580u 0:02.960 674Performance[5]: 10i 4.032ips 0.780e 9.580u 0:02.480 675Performance[6]: 10i 4.566ips 0.801e 9.640u 0:02.190 676Performance[7]: 10i 3.788ips 0.769e 10.980u 0:02.640 677Performance[8]: 10i 4.115ips 0.784e 12.030u 0:02.430 678Performance[9]: 10i 4.484ips 0.798e 12.860u 0:02.230 679Performance[10]: 10i 4.274ips 0.790e 14.830u 0:02.340 680Performance[11]: 10i 4.348ips 0.793e 16.500u 0:02.300 681Performance[12]: 10i 4.525ips 0.799e 18.320u 0:02.210 682</pre> 683<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> 684<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> 685 686<h2><a class="anchor" id="distributed"></a>Heterogeneous Distributed Processing</h2> 687<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> 688 689<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p> 690<pre class="highlight"><code>identify -version 691Features: DPC Cipher Modules OpenCL OpenMP(4.5) 692</code></pre> 693 694<p>If so, run this command to realize a significant speed-up for image convolution:</p> 695 696<pre class="highlight"><code>convert image.png -convolve '-1, -1, -1, -1, 9, -1, -1, -1, -1' convolve.png 697</code></pre> 698 699<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p> 700 701<p>Here is an example OpenCL kernel that convolves an image:</p> 702<pre class="pre-scrollable"><code>static inline long ClampToCanvas(const long offset,const ulong range) 703{ 704 if (offset < 0L) 705 return(0L); 706 if (offset >= range) 707 return((long) (range-1L)); 708 return(offset); 709} 710 711static inline CLQuantum ClampToQuantum(const float value) 712{ 713 if (value < 0.0) 714 return((CLQuantum) 0); 715 if (value >= (float) QuantumRange) 716 return((CLQuantum) QuantumRange); 717 return((CLQuantum) (value+0.5)); 718} 719 720__kernel void Convolve(const __global CLPixelType *source,__constant float *filter, 721 const ulong width,const ulong height,__global CLPixelType *destination) 722{ 723 const ulong columns = get_global_size(0); 724 const ulong rows = get_global_size(1); 725 726 const long x = get_global_id(0); 727 const long y = get_global_id(1); 728 729 const float scale = (1.0/QuantumRange); 730 const long mid_width = (width-1)/2; 731 const long mid_height = (height-1)/2; 732 float4 sum = { 0.0, 0.0, 0.0, 0.0 }; 733 float gamma = 0.0; 734 register ulong i = 0; 735 736 for (long v=(-mid_height); v <= mid_height; v++) 737 { 738 for (long u=(-mid_width); u <= mid_width; u++) 739 { 740 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u, 741 columns); 742 const float alpha=scale*(QuantumRange-source[index].w); 743 sum.x+=alpha*filter[i]*source[index].x; 744 sum.y+=alpha*filter[i]*source[index].y; 745 sum.z+=alpha*filter[i]*source[index].z; 746 sum.w+=filter[i]*source[index].w; 747 gamma+=alpha*filter[i]; 748 i++; 749 } 750 } 751 752 gamma=1.0/(fabs(gamma) <= MagickEpsilon ? 1.0 : gamma); 753 const ulong index=y*columns+x; 754 destination[index].x=ClampToQuantum(gamma*sum.x); 755 destination[index].y=ClampToQuantum(gamma*sum.y); 756 destination[index].z=ClampToQuantum(gamma*sum.z); 757 destination[index].w=ClampToQuantum(sum.w); 758};</code></pre> 759 760<p>See <a href="https://github.com/ImageMagick/ImageMagick/blob/master/MagickCore/accelerate.c">MagickCore/accelerate.c</a> for a complete implementation of image convolution with an OpenCL kernel.</p> 761 762<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> 763 764<h2><a class="anchor" id="coders"></a>Custom Image Coders</h2> 765 766<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> 767 768<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> 769<pre class="pre-scrollable"><code>#include <MagickCore/studio.h> 770#include <MagickCore/blob.h> 771#include <MagickCore/cache.h> 772#include <MagickCore/colorspace.h> 773#include <MagickCore/exception.h> 774#include <MagickCore/image.h> 775#include <MagickCore/list.h> 776#include <MagickCore/magick.h> 777#include <MagickCore/memory_.h> 778#include <MagickCore/monitor.h> 779#include <MagickCore/pixel-accessor.h> 780#include <MagickCore/string_.h> 781#include <MagickCore/module.h> 782#include "filter/blob-private.h" 783#include "filter/exception-private.h" 784#include "filter/image-private.h" 785#include "filter/monitor-private.h" 786#include "filter/quantum-private.h" 787 788/* 789 Forward declarations. 790*/ 791static MagickBooleanType 792 WriteMGKImage(const ImageInfo *,Image *,ExceptionInfo *); 793 794/* 795%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 796% % 797% % 798% % 799% I s M G K % 800% % 801% % 802% % 803%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 804% 805% IsMGK() returns MagickTrue if the image format type, identified by the 806% magick string, is MGK. 807% 808% The format of the IsMGK method is: 809% 810% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length) 811% 812% A description of each parameter follows: 813% 814% o magick: This string is generally the first few bytes of an image file 815% or blob. 816% 817% o length: Specifies the length of the magick string. 818% 819*/ 820static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length) 821{ 822 if (length < 7) 823 return(MagickFalse); 824 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0) 825 return(MagickTrue); 826 return(MagickFalse); 827} 828 829/* 830%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 831% % 832% % 833% % 834% R e a d M G K I m a g e % 835% % 836% % 837% % 838%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 839% 840% ReadMGKImage() reads a MGK image file and returns it. It allocates the 841% memory necessary for the new Image structure and returns a pointer to the 842% new image. 843% 844% The format of the ReadMGKImage method is: 845% 846% Image *ReadMGKImage(const ImageInfo *image_info, 847% ExceptionInfo *exception) 848% 849% A description of each parameter follows: 850% 851% o image_info: the image info. 852% 853% o exception: return any errors or warnings in this structure. 854% 855*/ 856static Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception) 857{ 858 char 859 buffer[MaxTextExtent]; 860 861 Image 862 *image; 863 864 long 865 y; 866 867 MagickBooleanType 868 status; 869 870 register long 871 x; 872 873 register Quantum 874 *q; 875 876 register unsigned char 877 *p; 878 879 ssize_t 880 count; 881 882 unsigned char 883 *pixels; 884 885 unsigned long 886 columns, 887 rows; 888 889 /* 890 Open image file. 891 */ 892 assert(image_info != (const ImageInfo *) NULL); 893 assert(image_info->signature == MagickCoreSignature); 894 if (image_info->debug != MagickFalse) 895 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s", 896 image_info->filename); 897 assert(exception != (ExceptionInfo *) NULL); 898 assert(exception->signature == MagickCoreSignature); 899 image=AcquireImage(image_info,exception); 900 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception); 901 if (status == MagickFalse) 902 { 903 image=DestroyImageList(image); 904 return((Image *) NULL); 905 } 906 /* 907 Read MGK image. 908 */ 909 (void) ReadBlobString(image,buffer); /* read magic number */ 910 if (IsMGK(buffer,7) == MagickFalse) 911 ThrowReaderException(CorruptImageError,"ImproperImageHeader"); 912 (void) ReadBlobString(image,buffer); 913 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows); 914 if (count <= 0) 915 ThrowReaderException(CorruptImageError,"ImproperImageHeader"); 916 do 917 { 918 /* 919 Initialize image structure. 920 */ 921 image->columns=columns; 922 image->rows=rows; 923 image->depth=8; 924 if ((image_info->ping != MagickFalse) && (image_info->number_scenes != 0)) 925 if (image->scene >= (image_info->scene+image_info->number_scenes-1)) 926 break; 927 /* 928 Convert MGK raster image to pixel packets. 929 */ 930 if (SetImageExtent(image,image->columns,image->rows,exception) == MagickFalse) 931 return(DestroyImageList(image)); 932 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns, 933 3UL*sizeof(*pixels)); 934 if (pixels == (unsigned char *) NULL) 935 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed"); 936 for (y=0; y < (long) image->rows; y++) 937 { 938 count=(ssize_t) ReadBlob(image,(size_t) (3*image->columns),pixels); 939 if (count != (ssize_t) (3*image->columns)) 940 ThrowReaderException(CorruptImageError,"UnableToReadImageData"); 941 p=pixels; 942 q=QueueAuthenticPixels(image,0,y,image->columns,1,exception); 943 if (q == (Quantum *) NULL) 944 break; 945 for (x=0; x < (long) image->columns; x++) 946 { 947 SetPixelRed(image,ScaleCharToQuantum(*p++),q); 948 SetPixelGreen(image,ScaleCharToQuantum(*p++),q); 949 SetPixelBlue(image,ScaleCharToQuantum(*p++),q); 950 q+=GetPixelChannels(image); 951 } 952 if (SyncAuthenticPixels(image,exception) == MagickFalse) 953 break; 954 if (image->previous == (Image *) NULL) 955 if ((image->progress_monitor != (MagickProgressMonitor) NULL) && 956 (QuantumTick(y,image->rows) != MagickFalse)) 957 { 958 status=image->progress_monitor(LoadImageTag,y,image->rows, 959 image->client_data); 960 if (status == MagickFalse) 961 break; 962 } 963 } 964 pixels=(unsigned char *) RelinquishMagickMemory(pixels); 965 if (EOFBlob(image) != MagickFalse) 966 { 967 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile", 968 image->filename); 969 break; 970 } 971 /* 972 Proceed to next image. 973 */ 974 if (image_info->number_scenes != 0) 975 if (image->scene >= (image_info->scene+image_info->number_scenes-1)) 976 break; 977 *buffer='\0'; 978 (void) ReadBlobString(image,buffer); 979 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows); 980 if (count > 0) 981 { 982 /* 983 Allocate next image structure. 984 */ 985 AcquireNextImage(image_info,image,exception); 986 if (GetNextImageInList(image) == (Image *) NULL) 987 { 988 image=DestroyImageList(image); 989 return((Image *) NULL); 990 } 991 image=SyncNextImageInList(image); 992 if (image->progress_monitor != (MagickProgressMonitor) NULL) 993 { 994 status=SetImageProgress(image,LoadImageTag,TellBlob(image), 995 GetBlobSize(image)); 996 if (status == MagickFalse) 997 break; 998 } 999 } 1000 } while (count > 0); 1001 (void) CloseBlob(image); 1002 return(GetFirstImageInList(image)); 1003} 1004 1005/* 1006%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1007% % 1008% % 1009% % 1010% R e g i s t e r M G K I m a g e % 1011% % 1012% % 1013% % 1014%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1015% 1016% RegisterMGKImage() adds attributes for the MGK image format to 1017% the list of supported formats. The attributes include the image format 1018% tag, a method to read and/or write the format, whether the format 1019% supports the saving of more than one frame to the same file or blob, 1020% whether the format supports native in-memory I/O, and a brief 1021% description of the format. 1022% 1023% The format of the RegisterMGKImage method is: 1024% 1025% unsigned long RegisterMGKImage(void) 1026% 1027*/ 1028ModuleExport unsigned long RegisterMGKImage(void) 1029{ 1030 MagickInfo 1031 *entry; 1032 1033 entry=AcquireMagickInfo("MGK","MGK","MGK image"); 1034 entry->decoder=(DecodeImageHandler *) ReadMGKImage; 1035 entry->encoder=(EncodeImageHandler *) WriteMGKImage; 1036 entry->magick=(IsImageFormatHandler *) IsMGK; 1037 (void) RegisterMagickInfo(entry); 1038 return(MagickImageCoderSignature); 1039} 1040 1041/* 1042%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1043% % 1044% % 1045% % 1046% U n r e g i s t e r M G K I m a g e % 1047% % 1048% % 1049% % 1050%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1051% 1052% UnregisterMGKImage() removes format registrations made by the 1053% MGK module from the list of supported formats. 1054% 1055% The format of the UnregisterMGKImage method is: 1056% 1057% UnregisterMGKImage(void) 1058% 1059*/ 1060ModuleExport void UnregisterMGKImage(void) 1061{ 1062 (void) UnregisterMagickInfo("MGK"); 1063} 1064 1065/* 1066%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1067% % 1068% % 1069% % 1070% W r i t e M G K I m a g e % 1071% % 1072% % 1073% % 1074%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1075% 1076% WriteMGKImage() writes an image to a file in red, green, and blue MGK 1077% rasterfile format. 1078% 1079% The format of the WriteMGKImage method is: 1080% 1081% MagickBooleanType WriteMGKImage(const ImageInfo *image_info, 1082% Image *image) 1083% 1084% A description of each parameter follows. 1085% 1086% o image_info: the image info. 1087% 1088% o image: The image. 1089% 1090% o exception: return any errors or warnings in this structure. 1091% 1092*/ 1093static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image, 1094 ExceptionInfo *exception) 1095{ 1096 char 1097 buffer[MaxTextExtent]; 1098 1099 long 1100 y; 1101 1102 MagickBooleanType 1103 status; 1104 1105 MagickOffsetType 1106 scene; 1107 1108 register const Quantum 1109 *p; 1110 1111 register long 1112 x; 1113 1114 register unsigned char 1115 *q; 1116 1117 unsigned char 1118 *pixels; 1119 1120 /* 1121 Open output image file. 1122 */ 1123 assert(image_info != (const ImageInfo *) NULL); 1124 assert(image_info->signature == MagickCoreSignature); 1125 assert(image != (Image *) NULL); 1126 assert(image->signature == MagickCoreSignature); 1127 if (image->debug != MagickFalse) 1128 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename); 1129 status=OpenBlob(image_info,image,WriteBinaryBlobMode,exception); 1130 if (status == MagickFalse) 1131 return(status); 1132 scene=0; 1133 do 1134 { 1135 /* 1136 Allocate memory for pixels. 1137 */ 1138 if (image->colorspace != RGBColorspace) 1139 (void) SetImageColorspace(image,RGBColorspace,exception); 1140 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns, 1141 3UL*sizeof(*pixels)); 1142 if (pixels == (unsigned char *) NULL) 1143 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed"); 1144 /* 1145 Initialize raster file header. 1146 */ 1147 (void) WriteBlobString(image,"id=mgk\n"); 1148 (void) FormatLocaleString(buffer,MaxTextExtent,"%lu %lu\n",image->columns, 1149 image->rows); 1150 (void) WriteBlobString(image,buffer); 1151 for (y=0; y < (long) image->rows; y++) 1152 { 1153 p=GetVirtualPixels(image,0,y,image->columns,1,exception); 1154 if (p == (const Quantum *) NULL) 1155 break; 1156 q=pixels; 1157 for (x=0; x < (long) image->columns; x++) 1158 { 1159 *q++=ScaleQuantumToChar(GetPixelRed(image,p)); 1160 *q++=ScaleQuantumToChar(GetPixelGreen(image,p)); 1161 *q++=ScaleQuantumToChar(GetPixelBlue(image,p)); 1162 p+=GetPixelChannels(image); 1163 } 1164 (void) WriteBlob(image,(size_t) (q-pixels),pixels); 1165 if (image->previous == (Image *) NULL) 1166 if ((image->progress_monitor != (MagickProgressMonitor) NULL) && 1167 (QuantumTick(y,image->rows) != MagickFalse)) 1168 { 1169 status=image->progress_monitor(SaveImageTag,y,image->rows, 1170 image->client_data); 1171 if (status == MagickFalse) 1172 break; 1173 } 1174 } 1175 pixels=(unsigned char *) RelinquishMagickMemory(pixels); 1176 if (GetNextImageInList(image) == (Image *) NULL) 1177 break; 1178 image=SyncNextImageInList(image); 1179 status=SetImageProgress(image,SaveImagesTag,scene, 1180 GetImageListLength(image)); 1181 if (status == MagickFalse) 1182 break; 1183 scene++; 1184 } while (image_info->adjoin != MagickFalse); 1185 (void) CloseBlob(image); 1186 return(MagickTrue); 1187}</code></pre> 1188 1189<p>To invoke the custom coder from the command line, use these commands:</p> 1190<pre class="highlight"><code>convert logo: logo.mgk 1191display logo.mgk 1192</code></pre> 1193 1194<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> 1195 1196<h2><a class="anchor" id="filters"></a>Custom Image Filters</h2> 1197 1198<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> 1199 1200<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> 1201<pre class="pre-scrollable"><code>#include <stdio.h> 1202#include <stdlib.h> 1203#include <string.h> 1204#include <time.h> 1205#include <assert.h> 1206#include <math.h> 1207#include <MagickCore/MagickCore.h> 1208 1209/* 1210%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1211% % 1212% % 1213% % 1214% a n a l y z e I m a g e % 1215% % 1216% % 1217% % 1218%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 1219% 1220% analyzeImage() computes the brightness and saturation mean, standard 1221% deviation, kurtosis and skewness and stores these values as attributes 1222% of the image. 1223% 1224% The format of the analyzeImage method is: 1225% 1226% size_t analyzeImage(Image *images,const int argc,char **argv, 1227% ExceptionInfo *exception) 1228% 1229% A description of each parameter follows: 1230% 1231% o image: the address of a structure of type Image. 1232% 1233% o argc: Specifies a pointer to an integer describing the number of 1234% elements in the argument vector. 1235% 1236% o argv: Specifies a pointer to a text array containing the command line 1237% arguments. 1238% 1239% o exception: return any errors or warnings in this structure. 1240% 1241*/ 1242 1243static void ConvertRGBToHSB(const double red,const double green, 1244 const double blue,double *hue,double *saturation,double *brightness) 1245{ 1246 double 1247 delta, 1248 max, 1249 min; 1250 1251 /* 1252 Convert RGB to HSB colorspace. 1253 */ 1254 assert(hue != (double *) NULL); 1255 assert(saturation != (double *) NULL); 1256 assert(brightness != (double *) NULL); 1257 *hue=0.0; 1258 *saturation=0.0; 1259 *brightness=0.0; 1260 min=red < green ? red : green; 1261 if (blue < min) 1262 min=blue; 1263 max=red > green ? red : green; 1264 if (blue > max) 1265 max=blue; 1266 if (fabs(max) < MagickEpsilon) 1267 return; 1268 delta=max-min; 1269 *saturation=delta/max; 1270 *brightness=QuantumScale*max; 1271 if (fabs(delta) < MagickEpsilon) 1272 return; 1273 if (fabs(red-max) < MagickEpsilon) 1274 *hue=(green-blue)/delta; 1275 else 1276 if (fabs(green-max) < MagickEpsilon) 1277 *hue=2.0+(blue-red)/delta; 1278 else 1279 *hue=4.0+(red-green)/delta; 1280 *hue/=6.0; 1281 if (*hue < 0.0) 1282 *hue+=1.0; 1283} 1284 1285ModuleExport size_t analyzeImage(Image **images,const int argc, 1286 const char **argv,ExceptionInfo *exception) 1287{ 1288 char 1289 text[MaxTextExtent]; 1290 1291 double 1292 area, 1293 brightness, 1294 brightness_mean, 1295 brightness_standard_deviation, 1296 brightness_kurtosis, 1297 brightness_skewness, 1298 brightness_sum_x, 1299 brightness_sum_x2, 1300 brightness_sum_x3, 1301 brightness_sum_x4, 1302 hue, 1303 saturation, 1304 saturation_mean, 1305 saturation_standard_deviation, 1306 saturation_kurtosis, 1307 saturation_skewness, 1308 saturation_sum_x, 1309 saturation_sum_x2, 1310 saturation_sum_x3, 1311 saturation_sum_x4; 1312 1313 Image 1314 *image; 1315 1316 assert(images != (Image **) NULL); 1317 assert(*images != (Image *) NULL); 1318 assert((*images)->signature == MagickCoreSignature); 1319 (void) argc; 1320 (void) argv; 1321 image=(*images); 1322 for ( ; image != (Image *) NULL; image=GetNextImageInList(image)) 1323 { 1324 CacheView 1325 *image_view; 1326 1327 long 1328 y; 1329 1330 MagickBooleanType 1331 status; 1332 1333 brightness_sum_x=0.0; 1334 brightness_sum_x2=0.0; 1335 brightness_sum_x3=0.0; 1336 brightness_sum_x4=0.0; 1337 brightness_mean=0.0; 1338 brightness_standard_deviation=0.0; 1339 brightness_kurtosis=0.0; 1340 brightness_skewness=0.0; 1341 saturation_sum_x=0.0; 1342 saturation_sum_x2=0.0; 1343 saturation_sum_x3=0.0; 1344 saturation_sum_x4=0.0; 1345 saturation_mean=0.0; 1346 saturation_standard_deviation=0.0; 1347 saturation_kurtosis=0.0; 1348 saturation_skewness=0.0; 1349 area=0.0; 1350 status=MagickTrue; 1351 image_view=AcquireVirtualCacheView(image,exception); 1352 for (y=0; y < (long) image->rows; y++) 1353 { 1354 register const Quantum 1355 *p; 1356 1357 register long 1358 x; 1359 1360 if (status == MagickFalse) 1361 continue; 1362 p=GetCacheViewVirtualPixels(image_view,0,y,image->columns,1,exception); 1363 if (p == (const Quantum *) NULL) 1364 { 1365 status=MagickFalse; 1366 continue; 1367 } 1368 for (x=0; x < (long) image->columns; x++) 1369 { 1370 ConvertRGBToHSB(GetPixelRed(image,p),GetPixelGreen(image,p), 1371 GetPixelBlue(image,p),&hue,&saturation,&brightness); 1372 brightness*=QuantumRange; 1373 brightness_sum_x+=brightness; 1374 brightness_sum_x2+=brightness*brightness; 1375 brightness_sum_x3+=brightness*brightness*brightness; 1376 brightness_sum_x4+=brightness*brightness*brightness*brightness; 1377 saturation*=QuantumRange; 1378 saturation_sum_x+=saturation; 1379 saturation_sum_x2+=saturation*saturation; 1380 saturation_sum_x3+=saturation*saturation*saturation; 1381 saturation_sum_x4+=saturation*saturation*saturation*saturation; 1382 area++; 1383 p+=GetPixelChannels(image); 1384 } 1385 } 1386 image_view=DestroyCacheView(image_view); 1387 if (area <= 0.0) 1388 break; 1389 brightness_mean=brightness_sum_x/area; 1390 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_mean); 1391 (void) SetImageProperty(image,"filter:brightness:mean",text,exception); 1392 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/ 1393 area*brightness_sum_x/area)); 1394 (void) FormatLocaleString(text,MaxTextExtent,"%g", 1395 brightness_standard_deviation); 1396 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text, 1397 exception); 1398 if (brightness_standard_deviation != 0) 1399 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean* 1400 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean* 1401 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean* 1402 brightness_mean*brightness_mean)/(brightness_standard_deviation* 1403 brightness_standard_deviation*brightness_standard_deviation* 1404 brightness_standard_deviation)-3.0; 1405 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_kurtosis); 1406 (void) SetImageProperty(image,"filter:brightness:kurtosis",text, 1407 exception); 1408 if (brightness_standard_deviation != 0) 1409 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean* 1410 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean* 1411 brightness_mean)/(brightness_standard_deviation* 1412 brightness_standard_deviation*brightness_standard_deviation); 1413 (void) FormatLocaleString(text,MaxTextExtent,"%g",brightness_skewness); 1414 (void) SetImageProperty(image,"filter:brightness:skewness",text,exception); 1415 saturation_mean=saturation_sum_x/area; 1416 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_mean); 1417 (void) SetImageProperty(image,"filter:saturation:mean",text,exception); 1418 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/ 1419 area*saturation_sum_x/area)); 1420 (void) FormatLocaleString(text,MaxTextExtent,"%g", 1421 saturation_standard_deviation); 1422 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text, 1423 exception); 1424 if (saturation_standard_deviation != 0) 1425 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean* 1426 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean* 1427 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean* 1428 saturation_mean*saturation_mean)/(saturation_standard_deviation* 1429 saturation_standard_deviation*saturation_standard_deviation* 1430 saturation_standard_deviation)-3.0; 1431 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_kurtosis); 1432 (void) SetImageProperty(image,"filter:saturation:kurtosis",text,exception); 1433 if (saturation_standard_deviation != 0) 1434 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean* 1435 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean* 1436 saturation_mean)/(saturation_standard_deviation* 1437 saturation_standard_deviation*saturation_standard_deviation); 1438 (void) FormatLocaleString(text,MaxTextExtent,"%g",saturation_skewness); 1439 (void) SetImageProperty(image,"filter:saturation:skewness",text,exception); 1440 } 1441 return(MagickImageFilterSignature); 1442} 1443</code></pre> 1444 1445<p>To invoke the custom filter from the command line, use this command:</p> 1446 1447<pre class="highlight"><code>convert logo: -process \"analyze\" -verbose info: 1448 Image: logo: 1449 Format: LOGO (ImageMagick Logo) 1450 Class: PseudoClass 1451 Geometry: 640x480 1452 ... 1453 filter:brightness:kurtosis: 8.17947 1454 filter:brightness:mean: 60632.1 1455 filter:brightness:skewness: -2.97118 1456 filter:brightness:standard-deviation: 13742.1 1457 filter:saturation:kurtosis: 4.33554 1458 filter:saturation:mean: 5951.55 1459 filter:saturation:skewness: 2.42848 1460 filter:saturation:standard-deviation: 15575.9 1461</code></pre> 1462 1463 1464<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> 1465 1466</div> 1467 </div> 1468 </main><!-- /.container --> 1469 <footer class="magick-footer"> 1470 <p><a href="security-policy.html">Security</a> • 1471 <a href="architecture.html">Architecture</a> 1472 1473 <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> 1474 1475 <a href="links.html">Related</a> • 1476 <a href="sitemap.html">Sitemap</a> 1477 <br/> 1478 <a href="support.html">Donate</a> • 1479 <a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> • 1480 <a href="https://imagemagick.org/script/contact.php">Contact Us</a> 1481 <br/> 1482 <small>© 1999-2020 ImageMagick Studio LLC</small></p> 1483 </footer> 1484 1485 <!-- Javascript assets --> 1486 <script src="assets/magick.js" crossorigin="anonymous"></script> 1487 <script>window.jQuery || document.write('<script src="https://localhost/ajax/libs/jquery/3.4.1/jquery.min.js"><\/script>')</script> 1488</body> 1489</html> 1490<!-- Magick Cache 5th January 2020 11:41 -->
