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cristy	16ff93c	2010-01-13 23:18:07 +0000	[diff] [blame^]	160	<p class="navigation-index">[<a href="#overview">Architecture Overview</a> • <a href="#cache">The Pixel Cache</a> • <a href="#stream">Streaming Pixels</a> • <a href="#properties">Image Properties and Profiles</a> • <a href="#threads">Threads of Execution</a> • <a href="#distributed">Heterogeneous Distributed Processing</a> • <a href="#coders">Custom Image Coders</a> • <a href="#filters">Custom Image Filters</a>]</p>
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	161
				162	<div class="doc-section">
				163	<p>The citizens of Oz were quite content with their benefactor, the all-powerful Wizard. They accepted his wisdom and benevolence without ever questioning the who, why, and where of his power. Like the citizens of Oz, if you feel comfortable that ImageMagick can help you convert, edit, or compose your images without knowing what goes on behind the curtain, feel free to skip this section. However, if you want to know more about the software and algorithms behind ImageMagick, read on. To fully benefit from this discussion, you should be comfortable with image nomenclature and be familiar with computer programming.</p>
				164	</div>
				165
				166	<h2><a name="overview"></a>Architecture Overview</h2>
				167	<div class="doc-section">
				168
				169	<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>
				170
				171	<ul>
				172	<li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
				173	<li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
				174	<li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
				175	<li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
				176	<li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
				177	<li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
				178	</ul>
				179
				180	<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>
				181
				182	<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
				183
				184	<ul>
				185	<li>one pixel a time (e.g. pixel at location 10,3)</li>
				186	<li>a single scanline (e.g. all pixels from row 4)</li>
				187	<li>a few scanlines at once (e.g. pixel rows 4-7)</li>
				188	<li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
				189	<li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
				190	<li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
				191	<li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
				192	<li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
				193	<li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
				194	<li>a high-dynamic range pixel that can include negative values as well as values that exceed the quantum depth (e.g. -0.00716)</li>
				195	<li>one or more pixels simultaneously in different threads of execution</li>
				196	</ul>
				197
				198	<p>In addition, some images include a clip mask that define which pixels are eligible to be updated. Pixels outside the area defined by the clip mask remain untouched.</p>
				199
				200	<p>Given the varied image formats and image processing requirements, we implemented the ImageMagick <a href="#cache">pixel cache</a> to provide convenient sequential or parallel access to any pixel on demand anywhere inside the image region and from any image in a sequence. In addition, the pixel cache permits access to pixels outside the boundaries defined by the image (we call these <a href="#virtual-pixels">virtual pixels</a>).</p>
				201
				202	<p>In addition to pixels, images have a plethora of <a href="#properties">image properties and profiles</a>. Properties include the well known items 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>
				203
				204	<p>ImageMagick consists of more than 375,000 lines of C code and optionally depends on several million lines of code in dependent libraries (e.g. JPEG, PNG, TIFF libraries). Given that, one might expect a huge architecture document. However, a great majority of image processing is simply accessing pixels and its metadata and our simple and elegant implementation makes this easy for the ImageMagick developer. We discuss the implementation of the pixel cache and getting and setting image properties and profiles in the next few sections. Next, we discuss using ImageMagick within a <a href="#threads">thread</a> of execution. In the final sections, we discuss <a href="#coders">image coders</a> to read or write a particular image format followed by a few words on creating a <a href="#filters">filter</a> to access or update pixels based on your custom requirements.</p>
				205
				206	</div>
				207
				208	<h2><a name="cache"></a>The Pixel Cache</h2>
				209	<div class="doc-section">
				210
				211	<p>The ImageMagick pixel cache is a repository for image pixels with up to 5 channels. The first 4 channels are stored contiguously and an optional second area follows with 1 channel. The channels are at the depth specified when ImageMagick was built. The channel depths are 8 bits-per-pixel component for the Q8 version of ImageMagick, 16 bits-per-pixel component for the Q16 version, and 32 bits-per-pixel component for the Q32 version. By default pixel components are unsigned quantities, however, if you use the <a href="../www/high-dynamic-range.html">high dynamic-range</a> version of ImageMagick, the components are 32-bit floating point. The primary 4 channels can hold any value but typically contain red, green, blue, and alpha intensities or cyan, magenta, yellow, and alpha intensities. The optional fifth channel contains the colormap indexes for colormapped images or the black channel for CMYK images. The pixel cache storage may be heap memory, anonymous memory mapped memory, disk-backed memory mapped, or on disk. The pixel cache is reference-counted. Only the cache properties are copied when the cache is cloned. The cache pixels are subsequently copied when you signal your intention to update any of the pixels.</p>
				212
				213	<h3>Create the Pixel Cache</h3>
				214	<div class="doc-section">
				215
				216	<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>
				217
				218	<h4>Create an image canvas initialized to the background color:</h4>
				219	<p class="code">
				220	image=AllocateImage(image_info);
				221	if (SetImageExtent(image,640,480) == MagickFalse)
				222	{ /* an exception was thrown */ }
				223	(void) QueryMagickColor("red",&image->background_color,&image->exception);
				224	SetImageBackgroundColor(image);
				225	</p>
				226
				227	<h4>Create an image from a JPEG image on disk:</h4>
				228	<p class="code"> (void) strcpy(image_info->filename,"image.jpg"):
				229	image=ReadImage(image_info,exception);
				230	if (image == (Image *) NULL)
				231	{ /* an exception was thrown */ }
				232	</p>
				233	<h4>Create an image from a memory based image:</h4>
				234	<p class="code">
				235	image=BlobToImage(blob_info,blob,extent,exception);
				236	if (image == (Image *) NULL)
				237	{ /* an exception was thrown */ }
				238	</p>
				239
				240	<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>
				241
				242	<p>When the pixel cache is initialized, pixels are scaled from whatever bit depth they originated from to that required by the pixel cache. For example, a 1-channel 1-bit monochrome PBM image is scaled to a 4 channel 8-bit RGBA image, if you are using the Q8 version of ImageMagick, and 16-bit RGBA for the Q16 version. You can determine which version you have using the <a href="../www/command-line-options.html#version">‑version</a> option, as with this command: </p>
				243
cristy	16ff93c	2010-01-13 23:18:07 +0000	[diff] [blame^]	244	<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.5.9-0 2010-01-01 Q16 http://www.imagemagick.org</span></p>
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	245	<p>As you can see, the convenience of the pixel cache sometimes comes with a trade-off in storage (e.g. storing a 1-bit monochrome image as 16-bit RGBA is wasteful) and speed (i.e. storing the entire image in memory is generally slower than accessing one scanline of pixels at a time).</p>
				246	</div>
				247
				248	<h3>Access the Pixel Cache</h3>
				249	<div class="doc-section">
				250
				251	<p>Once the pixel cache is associated with an image, you typically want to get, update, or put pixels into it. We refer to pixels inside the image region as <em>authentic pixels</em> and outside the region as <em>virtual pixels</em>. Use these methods to access the pixels in the cache:</p>
				252	<ul>
				253	<li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify</li>
				254	<li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
				255	<li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
				256	<li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
				257	</ul>
				258
				259	<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>
				260
				261	<div class="viewport">
				262	<pre class="code">
				263	long
				264	x,
				265	y;
				266
				267	const PixelPacket
				268	*p;
				269
				270	PixelPacket
				271	*q;
				272
				273	destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
				274	if (destination == (Image *) NULL)
				275	{ /* an exception was thrown */ }
				276	for (y=0; y < (long) source->rows; y++)
				277	{
				278	p=GetVirtualPixels(source,0,y,source->columns,1,exception);
				279	q=GetAuthenticPixels(destination,0,y,destination->columns,1,exception);
				280	if ((p == (const PixelPacket ) NULL) \|\| (q == (PixelPacket ) NULL)
				281	break;
				282	for (x=0; x < (long) source->columns; x++)
				283	{
				284	q->red=90*p->red/100;
				285	q->green=90*p->green/100;
				286	q->blue=90*p->blue/100;
				287	q->opacity=90*p->opacity/100;
				288	p++;
				289	q++;
				290	}
				291	if (SyncAuthenticPixels(destination,exception) == MagickFalse)
				292	break;
				293	}
				294	if (y < (long) source->rows)
				295	{ /* an exception was thrown */ }
				296	</pre>
				297	</div>
				298
				299	<p>When we first create the destination image by cloning the source image, the pixel cache pixels are not copied. They are only copied when you signal your intentions to modify the pixel cache by calling <a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> or <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a>. Use <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> if you want to set new pixel values rather than update existing ones. Finally, use <a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p>
				300
				301	<p>Recall how we mentioned that the indexes of a colormapped image or the black channel of a CMYK image are stored separately. Use <a href="../www/api/cache.html#GetVirtualIndexes">GetVirtualIndexes()</a> (to read the indexes) or <a href="../www/api/cache.html#GetAuthenticIndexes">GetAuthenticIndexes()</a> (to update the indexes) to gain access to this channel. For example, to print the colormap indexes, use:</p>
				302
				303	<pre class="code">
				304	const IndexPacket
				305	*indexes;
				306
				307	for (y=0; y < (long) source->rows; y++)
				308	{
				309	p=GetVirtualPixels(source,0,y,source->columns,1);
				310	if (p == (const PixelPacket *) NULL)
				311	break;
				312	indexes=GetVirtualIndexes(source);
				313	for (x=0; x < (long) source->columns; x++)
				314	(void) printf("%d\n",indexes[x];
				315	}
				316	if (y < (long) source->rows)
				317	/* an exception was thrown */
				318	</pre>
				319
				320	<p>The pixel cache manager decides whether to give you direct or indirect access to the image pixels. In some cases the pixels are staged to an intermediate buffer-- and that is why you must call SyncAuthenticPixels() to ensure this buffer is <em>pushed</em> out to the pixel cache to guarantee the corresponding pixels in the cache are updated. For this reason we recommend that you only read or update a scanline or a few scanlines of pixels at a time. However, you can get any rectangular region of pixels you want. GetAuthenticPixels() requires that the region you request is within the bounds of the image area. For a 640 by 480 image, you can get a scanline of 640 pixels but if you ask for 641 pixels, an exception is returned. GetVirtualPixels() does not have this constraint. For example,</p>
				321
				322	<pre class="code">
				323	p=GetVirtualPixels(source,-3,3,source->columns+7,7,exception);
				324	</pre>
				325
				326	<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
				327	</div>
				328
				329	<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
				330	<div class="doc-section">
				331
				332	<p>Access to the virtual pixels are controlled by the <a href="../www/api/cache.html#SetImageVirtualPixelMethod">SetImageVirtualPixelMethod()</a> method from the MagickCore API or the <a href="../www/command-line-options.html#virtual-pixel">‑virtual‑pixel</a> option from the command line. The methods include:</p>
				333
				334	<pre class="text">
				335	background: the area surrounding the image is the background color
				336	black: the area surrounding the image is black
				337	checker-tile: alternate squares with image and background color
				338	dither: non-random 32x32 dithered pattern
				339	edge: extend the edge pixel toward infinity
				340	gray: the area surrounding the image is gray
				341	horizontal-tile: horizontally tile the image, background color above/below
				342	horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
				343	mirror: mirror tile the image
				344	random: choose a random pixel from the image
				345	tile: tile the image (default)
				346	transparent: the area surrounding the image is transparent blackness
				347	vertical-tile: vertically tile the image, sides are background color
				348	vertical-tile-edge: vertically tile the image and replicate the side edge pixels
				349	white: the area surrounding the image is white
				350	</pre>
				351
				352	<p>There is a plethora of image processing algorithms that require a neighborhood of pixels about a pixel of interest. There is typically 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>
				353	</div>
				354
				355	<h3>Cache Storage and Resource Requirements</h3>
				356	<div class="doc-section">
				357
cristy	c1c6166	2009-09-30 14:04:37 +0000	[diff] [blame]	358	<p>We mentioned previously 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're using the Q16 version of ImageMagick, the pixel cache consumes image <em>width * height * bit-depth / 8 * channels</em> bytes or approximately 2.3 mebibytes (i.e. 640 * 480 * 2 * 4). Not too bad, but what if your image is 25000 by 25000 pixels? The pixel cache requires approximately 4.7 gibibytes of storage. Ouch. ImageMagick accounts for possible huge storage requirements by caching large images to disk rather than memory. Typically the pixel cache is stored in memory using heap memory. If heap memory is exhausted, pixels are stored in in an anonymous map; if the anonymous memory map is exhausted, we create the pixel cache on disk and attempt to memory-map it; and if memory-map memory is exhausted, we simply use standard disk I/O. Disk storage is cheap but it is also very slow, upwards of 1000 times slower than memory. We can get some speed improvements, up to 5 times, if we use memory mapping to the disk-based cache. These decisions about storage are made <em>automagically</em> by the pixel cache manager negotiating with the operating system. However, you can influence how the pixel cache manager allocates the pixel cache with <em>cache resource limits</em>. The limits include:</p>
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	359
				360	<dl class="doc">
				361	<dt class="doc">files</dt>
				362	<dd>maximum number of open pixel cache files. When this limit is exceeded, any subsequent pixels cached to disk are closed and reopened on demand. This behavior permits a large number of images to be accessed simultaneously on disk, but with a speed penalty due to repeated open/close calls.</dd>
				363	<dt class="doc">area</dt>
				364	<dd>maximum area in bytes of any one image that can reside in the pixel cache memory. If this limit is exceeded, the image is automagically cached to disk.</dd>
				365	<dt class="doc">memory</dt>
				366	<dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
				367	<dt class="doc">map</dt>
				368	<dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
				369	<dt class="doc">disk</dt>
				370	<dd>maximum amount of disk space in bytes permitted for use by the pixel cache. If this limit is exceeded, the pixel cache is not created and a fatal exception is thrown.</dd>
				371	</dl>
				372
				373	<p>To determine the current setting of these limits, use this command:</p>
				374
cristy	c1c6166	2009-09-30 14:04:37 +0000	[diff] [blame]	375	<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>identify -list resource</span><span class='crtout'><pre>File Area Memory Map Disk Thread Time
				376	------------------------------------------------------------------------
				377	768 11.551GiB 8.6631GiB 23.102GiB 16EiB 8 unlimited</pre></span></p>
				378	<p>You can set these limits either with <a href="../www/resources.html#environment">environment variables</a>, the <a href="../www/command-line-options.html#limit">-limit</a> command line option, or the <a href="../www/api/resource.html#SetMagickResourceLimit">SetMagickResourceLimit()</a> MagickCore API method. As an example, our online web interface to ImageMagick, <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">ImageMagick Studio</a>, has an area limit of 64 mebibytes, a memory limit of 128 mebibytes and a map limit of 256 mebibytes and a disk limit of 1 gibibytes. Since we process multiple simultaneous sessions, we don't want any one session consuming all the available memory. Instead large images are cached to disk. If the image is too large and exceeds the pixel cache disk limit, the program exits. In addition, we place a 60 second time limit to prevent any run-away processing tasks.</p>
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	379
				380	<p>Note, the cache limits are global, meaning if you create several images, the combined resource requirements are compared to the limit to determine the pixel cache storage disposition.</p>
				381	</div>
				382
				383	<h3>Cache Views</h3>
				384	<div class="doc-section">
				385
				386	<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() from the MagickCore API can only deal with one pixel cache area per image at a time. Suppose you want to access the first and last scanline from the same image at the same time? The solution is to use a <em>cache view</em>. A cache view permits you to access as many areas simultaneously in the pixel cache as you require. The cache view <a href="../www/api/cache-view.html">methods</a> behave like the previous methods except you must first open a view and close it when you are finished with it. Here is a snippet of MagickCore code that permits us to access two areas of an image simultaneously:</p>
				387
				388	<pre class="code">
				389	CacheView
				390	*view_1,
				391	*view_2;
				392
				393	view_1=OpenCacheView(source);
				394	view_2=OpenCacheView(source);
				395	for (y=0; y < (long) source->rows; y++)
				396	{
				397	u=GetCacheViewVirtualPixels(view_1,0,y,source->columns,1,exception);
				398	v=GetCacheViewVirtualPixels(view_2,0,source->rows-y-1,source->columns,1,exception);
				399	if ((u == (const PixelPacket ) NULL) \|\| (v == (const PixelPacket ) NULL))
				400	break;
				401	for (x=0; x < (long) source->columns; x++)
				402	{
				403	/* do something with u & v here */
				404	}
				405	}
				406	view_1=CloseCacheView(view_1);
				407	view_2=CloseCacheView(view_2);
				408	if (y < (long) source->rows)
				409	{ /* an exception was thrown */ }
				410	</pre>
				411	</div>
				412
				413	<h3>Magick Persistent Cache Format</h3>
				414	<div class="doc-section">
				415
				416	<p>Recall that each image format is decoded by ImageMagick and the pixels are deposited in the pixel cache. If you write an image, the pixels are read from the pixel cache and encoded as required by the format you are writing (e.g. GIF, PNG, etc.). The Magick Persistent Cache (MPC) format is designed to eliminate the overhead of decoding and encoding pixels to and from an image format. MPC writes two files. One, with the extension <kbd>.mpc</kbd>, retains all the properties associated with the image or image sequence (e.g. width, height, colorspace, etc.) and the second, with the extension <kbd>.cache</kbd>, is the pixel cache in the native format. When reading an MPC image file, ImageMagick reads the image properties and memory maps the pixel cache on disk eliminating the need for decoding the image pixels. The tradeoff is in disk space. MPC is generally larger in file size than most other image formats.</p>
				417	</div>
				418
				419	<h3>Best Practices</h3>
				420	<div class="doc-section">
				421
				422	<p>Although you can request any pixel from the pixel cache, any block of pixels, any scanline, multiple scanlines, any row, or multiple rows with the GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels, GetCacheViewVirtualPixels(), GetCacheViewAuthenticPixels(), and QueueCacheViewAuthenticPixels() methods, ImageMagick is optimized to return a few pixels or a few pixels rows at time. There are additional optimizations if you request a single scanline or a few scanlines at a time. These methods also permit random access to the pixel cache, however, ImageMagick is optimized for sequential access.</p>
				423
				424	<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>
				425
				426	<p>Use QueueAuthenticPixels() or QueueCacheViewAuthenticPixels() if you are setting an initial pixel value. The GetAuthenticPixels() or GetCacheViewAuthenticPixels() method reads pixels from the cache and if you are setting an initial pixel value, this read is unnecessary. Don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to push your updates to the pixel cache.</p>
				427
				428	<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() are slightly more efficient than their cache view counter-parts. However, cache views are required if you need access to more than one region of the image simultaneously or if more than one <a href="#threads">thread of execution</a> is accessing the image.</p>
				429
				430	<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>
				431
				432	<p>Although you can force the pixel cache to disk using appropriate resource limits, disk access can be upwards of 1000 times slower than memory access. For fast, efficient, access to the pixel cache, try to keep the pixel cache in heap memory or anonymous mapped memory.</p>
				433
				434	<p>The ImageMagick Q16 version of ImageMagick permits you to read and write 16 bit images without scaling but the pixel cache consumes twice as much resources as the Q8 version. If your system has constrained memory or disk resources, consider the Q8 version of ImageMagick. In addition, the Q8 version typically executes faster than the Q16 version.</p>
				435
				436	<p>A great majority of image formats and algorithms restrict themselves to a fixed range of pixel values from 0 to some maximum value, for example, the Q16 version of ImageMagick permit intensities from 0 to 65535. High dynamic-range imaging (HDRI), however, permits a far greater dynamic range of exposures (i.e. a large difference between light and dark areas) than standard digital imaging techniques. HDRI accurately represents the wide range of intensity levels found in real scenes ranging from the brightest direct sunlight to the deepest darkest shadows. Enable <a href="../www/high-dynamic-range.html">HDRI</a> at ImageMagick build time to deal with high dynamic-range images, but be mindful that each pixel component is a 32-bit floating point value. In addition pixel values are not clamped so some algorithms may perform differently than the non-HDRI version.</p>
				437
cristy	739df91	2009-10-24 16:10:18 +0000	[diff] [blame]	438	<p>If you are dealing with large images, make sure the pixel cache is written to a disk area with plenty of free space. Under Unix, this is typically <kbd>/tmp</kbd> and for Windows, <kbd>c:/temp</kbd>. You can tell ImageMagick to write the pixel cache to an alternate location with the MAGICK_TEMPORARY_PATH environment variable. For example,</p>
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	439
cristy	739df91	2009-10-24 16:10:18 +0000	[diff] [blame]	440	<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>export MAGICK_TEMPORARY_PATH=/data/magick</span></p>
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	441
				442	<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>
				443
				444	<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.tif image.mpc</span><span class='crtout'></span><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.mpc -crop 100x100+0+0 +repage 1.png</span><span class='crtout'></span><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.mpc -crop 100x100+100+0 +repage 2.png</span><span class='crtout'></span><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.mpc -crop 100x100+200+0 +repage 3.png</span></p>
				445	<p>MPC is ideal for web sites. It reduces the overhead of reading and writing an image. We use it exclusively at our <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">online image studio</a>.</p>
				446	</div>
				447
				448	</div>
				449
				450	<h2><a name="stream"></a>Streaming Pixels</h2>
				451	<div class="doc-section">
				452
				453	<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>
				454
				455	<p>Use <a href="../www/api/stream.html#ReadStream">ReadStream()</a> or <a href="../www/api/stream.html#WriteStream">WriteStream()</a> with an appropriate callback method in your MagickCore program to consume the pixels as they are streaming. Here's an abbreviated example of using ReadStream:</p>
				456
				457	<pre class="code">
				458	static size_t StreamHandler(const Image image,const void pixels,
				459	const size_t columns)
				460	{
				461	/* process pixels here */
				462	return(columns);
				463	}
				464
				465	...
				466	/* invoke the pixel stream here */
				467	image=ReadStream(image_info,&StreamHandler,exception);
				468	</pre>
				469
				470	<p>We also provide a lightweight tool, <a name="stream"></a><a href="../www/stream.html">stream</a>, to stream one or more pixel components of the image or portion of the image to your choice of storage formats. It writes the pixel components as they are read from the input image a row at a time making <a name="stream"></a><a href="../www/stream.html">stream</a> desirable when working with large images or when you require raw pixel components.</p>
				471
				472	</div>
				473
				474	<h2><a name="properties"></a>Image Properties and Profiles</h2>
				475	<div class="doc-section">
				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
				479	<pre class="code">
				480	(void) printf("image width: %lu, height: %lu\n",image->columns,image->rows);
				481	</pre>
				482
				483	<p>For a great majority of image properties, such as an image comment or description, we use the <a href="../www/api/property.html#GetImageProperty">GetImageProperty()</a> and <a href="../www/api/property.html#SetImageProperty">SetImageProperty()</a> methods. Here we set a property and fetch it right back:</p>
				484
				485	<pre class="code">
				486	const char
				487	*comment;
				488
				489	(void) SetImageProperty(image,"comment","This space for rent");
				490	comment=GetImageProperty(image,"comment");
				491	if (comment == (const char *) NULL)
				492	(void) printf("Image comment: %s\n",comment);
				493	</pre>
				494
				495	<p>Image profiles are handled with <a href="../www/api/profile.html#GetImageProfile">GetImageProfile()</a>, <a href="../www/api/profile.html#SetImageProfile">SetImageProfile()</a>, and <a href="../www/api/profile.html#ProfileImage">ProfileImage()</a> methods. Here we set a profile and fetch it right back:</p>
				496
				497	<pre class="code">
				498	StringInfo
				499	*profile;
				500
				501	profile=AcquireStringInfo(length);
				502	SetStringInfoDatum(profile,my_exif_profile);
				503	(void) SetImageProfile(image,"EXIF",profile);
				504	DestroyStringInfo(profile);
				505	profile=GetImageProfile(image,"EXIF");
				506	if (profile != (StringInfo *) NULL)
				507	(void) PrintStringInfo(stdout,"EXIF",profile);
				508	</pre>
				509
				510	</div>
				511
				512	<h2><a name="threads"></a>Threads of Execution</h2>
				513	<div class="doc-section">
				514
				515	<p>Many of ImageMagick's internal algorithms are threaded to take advantage of speed-ups offered by the dual and quad-core processor technologies. However, you are welcome to use ImageMagick algorithms in your threads of execution with the exception of the MagickCore's GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), or SyncAuthenticPixels() pixel cache methods. These methods are intended for one thread of execution only. To access the pixel cache with more than one thread of execution, use a cache view. We do this for the <a href="../www/api/composite.html#CompositeImage">CompositeImage()</a> method, for example. Suppose we want to composite a single image over a different image in each thread of execution. If we use GetVirtualPixels(), the results are unpredictable because multiple threads would likely be asking for different areas of the pixel cache simultaneously. Instead we use GetCacheViewVirtualPixels() which creates a unique view for each thread of execution ensuring our program behaves properly regardless of how many threads are invoked. The other program interfaces, such as the <a href="../www/magick-wand.html">MagickWand API</a>, are completely thread safe so there are no special precautions for threads of execution.</p>
				516
cristy	16ff93c	2010-01-13 23:18:07 +0000	[diff] [blame^]	517	<p>Here is an example of how ImageMagick can take advantage of threads of execution with the <a href="http://en.wikipedia.org/wiki/OpenMP">OpenMP</a> programming paradigm:</p>
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	518
				519	<div class="viewport">
				520	<pre class="code">
				521	{
				522	CacheView
				523	*image_view;
				524
				525	long
				526	y;
				527
				528	MagickBooleanType
				529	status;
				530
				531	status=MagickTrue;
				532	image_view=AcquireCacheView(image);
				533	#pragma omp parallel for schedule(dynamic,4) shared(status)
				534	for (y=0; y < (long) image->rows; y++)
				535	{
				536	register IndexPacket
				537	*indexes;
				538
				539	register long
				540	x;
				541
				542	register PixelPacket
				543	*q;
				544
				545	if (status == MagickFalse)
				546	continue;
				547	q=GetCacheViewAuthenticPixels(image_view,0,y,image->columns,1,exception);
				548	if (q == (PixelPacket *) NULL)
				549	{
				550	status=MagickFalse;
				551	continue;
				552	}
				553	indexes=GetCacheViewAuthenticIndexQueue(image_view);
				554	for (x=0; x < (long) image->columns; x++)
				555	{
				556	q->red= ...
				557	q->green= ...
				558	q->blue= ...
				559	q->opacity= ...
				560	if (indexes != (IndexPacket *) NULL)
				561	indexes[x]= ...
				562	q++;
				563	}
				564	if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
				565	status=MagickFalse;
				566	}
				567	image_view=DestroyCacheView(image_view);
				568	if (status == MagickFalse)
				569	perror("something went wrong");
				570	}
				571	</pre>
				572	</div>
				573
				574	<p>If you call the ImageMagick API from your OpenMP-enabled application and you intend to dynamically increase the number of threads available in subsequent parallel regions, be sure to perform the increase <em>before</em> you call the API otherwise ImageMagick may fault.</p>
				575
				576	</div>
				577
cristy	16ff93c	2010-01-13 23:18:07 +0000	[diff] [blame^]	578	<h2><a name="distributed"></a>Heterogeneous Distributed Processing</h2>
				579	<div class="doc-section">
				580	<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>
				581
				582	<p>To speed up image convolution, for example, use this image filter:</p>
				583
				584	<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert image.pam -process "convolve '-1, -1, -1, -1, 9, -1, -1, -1, -1'" gpu.pam</span></p>
				585	<p>Here is an example OpenCL kernel that convolves an image:</p>
				586
				587	<div class="viewport">
				588	<pre class="code">
				589	static inline long ClampToCanvas(const long offset,const ulong range)
				590	{
				591	if (offset < 0L)
				592	return(0L);
				593	if (offset >= range)
				594	return((long) (range-1L));
				595	return(offset);
				596	}
				597
				598	static inline CLQuantum ClampToQuantum(const double value)
				599	{
				600	if (value < 0.0)
				601	return((CLQuantum) 0);
				602	if (value >= (double) QuantumRange)
				603	return((CLQuantum) QuantumRange);
				604	return((CLQuantum) (value+0.5));
				605	}
				606
				607	__kernel void Convolve(const __global CLPixelType source,__constant double filter,
				608	const ulong width,const ulong height,__global CLPixelType *destination)
				609	{
				610	const ulong columns = get_global_size(0);
				611	const ulong rows = get_global_size(1);
				612
				613	const long x = get_global_id(0);
				614	const long y = get_global_id(1);
				615
				616	const double scale = (1.0/QuantumRange);
				617	const long mid_width = (width-1)/2;
				618	const long mid_height = (height-1)/2;
				619	double4 sum = { 0.0, 0.0, 0.0, 0.0 };
				620	double gamma = 0.0;
				621	register ulong i = 0;
				622
				623	for (long v=(-mid_height); v <= mid_height; v++)
				624	{
				625	for (long u=(-mid_width); u <= mid_width; u++)
				626	{
				627	register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,columns);
				628	const double alpha=scale*(QuantumRange-source[index].w);
				629	sum.x+=alphafilter[i]source[index].x;
				630	sum.y+=alphafilter[i]source[index].y;
				631	sum.z+=alphafilter[i]source[index].z;
				632	sum.w+=filter[i]*source[index].w;
				633	gamma+=alpha*filter[i];
				634	i++;
				635	}
				636	}
				637
				638	gamma=1.0/(fabs(gamma) <= MagickEpsilon ? 1.0 : gamma);
				639	const ulong index=y*columns+x;
				640	destination[index].x=ClampToQuantum(gamma*sum.x);
				641	destination[index].y=ClampToQuantum(gamma*sum.y);
				642	destination[index].z=ClampToQuantum(gamma*sum.z);
				643	destination[index].w=ClampToQuantum(sum.w);
				644	};
				645	</pre>
				646	</div>
				647
				648	<p>See <a href="http://trac.imagemagick.org/browser/ImageMagick/trunk/filters/convolve.c">filters/convolve.c</a> for a complete implementation of image convolution with an OpenCL kernel.</p>
				649
				650	</div>
				651
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	652	<h2><a name="coders"></a>Custom Image Coders</h2>
				653	<div class="doc-section">
				654
				655	<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>
				656
				657	<p>Here is a listing of a sample <a href="../www/source/mgk.c">custom coder</a>. It reads and writes images in the MGK image format which is simply an ID followed by the image width and height followed by the RGB pixel values.</p>
				658
				659	<div class="viewport">
				660	<pre class="code">
				661	/*
				662	Include declarations.
				663	*/
				664	#include "magick/studio.h"
				665	#include "magick/blob.h"
				666	#include "magick/blob-private.h"
				667	#include "magick/colorspace.h"
				668	#include "magick/exception.h"
				669	#include "magick/exception-private.h"
				670	#include "magick/image.h"
				671	#include "magick/image-private.h"
				672	#include "magick/list.h"
				673	#include "magick/magick.h"
				674	#include "magick/memory_.h"
				675	#include "magick/monitor.h"
				676	#include "magick/monitor-private.h"
				677	#include "magick/quantum-private.h"
				678	#include "magick/static.h"
				679	#include "magick/string_.h"
				680	#include "magick/module.h"
				681
				682	/*
				683	Forward declarations.
				684	*/
				685	static MagickBooleanType
				686	WriteMGKImage(const ImageInfo ,Image );
				687
				688	/*
				689	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				690	% %
				691	% %
				692	% %
				693	% I s M G K %
				694	% %
				695	% %
				696	% %
				697	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				698	%
				699	% IsMGK() returns MagickTrue if the image format type, identified by the
				700	% magick string, is MGK.
				701	%
				702	% The format of the IsMGK method is:
				703	%
				704	% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
				705	%
				706	% A description of each parameter follows:
				707	%
				708	% o magick: This string is generally the first few bytes of an image file
				709	% or blob.
				710	%
				711	% o length: Specifies the length of the magick string.
				712	%
				713	*/
				714	static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
				715	{
				716	if (length < 7)
				717	return(MagickFalse);
				718	if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
				719	return(MagickTrue);
				720	return(MagickFalse);
				721	}
				722
				723	/*
				724	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				725	% %
				726	% %
				727	% %
				728	% R e a d M G K I m a g e %
				729	% %
				730	% %
				731	% %
				732	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				733	%
				734	% ReadMGKImage() reads a MGK image file and returns it. It allocates
				735	% the memory necessary for the new Image structure and returns a pointer to
				736	% the new image.
				737	%
				738	% The format of the ReadMGKImage method is:
				739	%
				740	% Image ReadMGKImage(const ImageInfo image_info,ExceptionInfo *exception)
				741	%
				742	% A description of each parameter follows:
				743	%
				744	% o image_info: the image info.
				745	%
				746	% o exception: return any errors or warnings in this structure.
				747	%
				748	*/
				749	static Image ReadMGKImage(const ImageInfo image_info,
				750	ExceptionInfo *exception)
				751	{
				752	char
				753	buffer[MaxTextExtent];
				754
				755	Image
				756	*image;
				757
				758	long
				759	y;
				760
				761	MagickBooleanType
				762	status;
				763
				764	register long
				765	x;
				766
				767	register PixelPacket
				768	*q;
				769
				770	register unsigned char
				771	*p;
				772
				773	ssize_t
				774	count;
				775
				776	unsigned char
				777	*pixels;
				778
				779	unsigned long
				780	columns,
				781	rows;
				782
				783	/*
				784	Open image file.
				785	*/
				786	assert(image_info != (const ImageInfo *) NULL);
				787	assert(image_info->signature == MagickSignature);
				788	if (image_info->debug != MagickFalse)
				789	(void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info->filename);
				790	assert(exception != (ExceptionInfo *) NULL);
				791	assert(exception->signature == MagickSignature);
				792	image=AcquireImage(image_info);
				793	status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
				794	if (status == MagickFalse)
				795	{
				796	image=DestroyImageList(image);
				797	return((Image *) NULL);
				798	}
				799	/*
				800	Read MGK image.
				801	*/
				802	(void) ReadBlobString(image,buffer); /* read magic number */
				803	if (IsMGK(buffer,7) == MagickFalse)
				804	ThrowReaderException(CorruptImageError,"ImproperImageHeader");
				805	(void) ReadBlobString(image,buffer);
				806	count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows);
				807	if (count <= 0)
				808	ThrowReaderException(CorruptImageError,"ImproperImageHeader");
				809	do
				810	{
				811	/*
				812	Initialize image structure.
				813	*/
				814	image->columns=columns;
				815	image->rows=rows;
				816	image->depth=8;
				817	if ((image_info->ping != MagickFalse) && (image_info->number_scenes != 0))
				818	if (image->scene >= (image_info->scene+image_info->number_scenes-1))
				819	break;
				820	/*
				821	Convert MGK raster image to pixel packets.
				822	*/
				823	if (SetImageExtent(image,0,0) == MagickFalse)
				824	{
				825	InheritException(exception,&image->exception);
				826	return(DestroyImageList(image));
				827	}
				828	pixels=(unsigned char ) AcquireQuantumMemory((size_t) image->columns,3ULsizeof(*pixels));
				829	if (pixels == (unsigned char *) NULL)
				830	ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
				831	for (y=0; y < (long) image->rows; y++)
				832	{
				833	count=(ssize_t) ReadBlob(image,(size_t) (3*image->columns),pixels);
				834	if (count != (ssize_t) (3*image->columns))
				835	ThrowReaderException(CorruptImageError,"UnableToReadImageData");
				836	p=pixels;
				837	q=QueueAuthenticPixels(image,0,y,image->columns,1,exception);
				838	if (q == (PixelPacket *) NULL)
				839	break;
				840	for (x=0; x < (long) image->columns; x++)
				841	{
				842	q->red=ScaleCharToQuantum(*p++);
				843	q->green=ScaleCharToQuantum(*p++);
				844	q->blue=ScaleCharToQuantum(*p++);
				845	q++;
				846	}
				847	if (SyncAuthenticPixels(image,exception) == MagickFalse)
				848	break;
				849	if ((image->previous == (Image *) NULL) &&
				850	(SetImageProgress(image,LoadImageTag,y,image>>rows) == MagickFalse))
				851	break;
				852	}
				853	pixels=(unsigned char *) RelinquishMagickMemory(pixels);
				854	if (EOFBlob(image) != MagickFalse)
				855	{
				856	ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image->filename);
				857	break;
				858	}
				859	/*
				860	Proceed to next image.
				861	*/
				862	if (image_info->number_scenes != 0)
				863	if (image->scene >= (image_info->scene+image_info->number_scenes-1))
				864	break;
				865	*buffer='\0';
				866	(void) ReadBlobString(image,buffer);
				867	count=(ssize_t) sscanf(buffer,"%lu %lu\n",&columns,&rows);
				868	if (count != 0)
				869	{
				870	/*
				871	Allocate next image structure.
				872	*/
				873	AcquireNextImage(image_info,image);
				874	if (GetNextImageInList(image) == (Image *) NULL)
				875	{
				876	image=DestroyImageList(image);
				877	return((Image *) NULL);
				878	}
				879	image=SyncNextImageInList(image);
				880	status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
				881	if (status == MagickFalse)
				882	break;
				883	}
				884	} while (count != 0);
				885	(void) CloseBlob(image);
				886	return(GetFirstImageInList(image));
				887	}
				888
				889	/*
				890	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				891	% %
				892	% %
				893	% %
				894	% R e g i s t e r M G K I m a g e %
				895	% %
				896	% %
				897	% %
				898	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				899	%
				900	% RegisterMGKImage() adds attributes for the MGK image format to
				901	% the list of supported formats. The attributes include the image format
				902	% tag, a method to read and/or write the format, whether the format
				903	% supports the saving of more than one frame to the same file or blob,
				904	% whether the format supports native in-memory I/O, and a brief
				905	% description of the format.
				906	%
				907	% The format of the RegisterMGKImage method is:
				908	%
				909	% unsigned long RegisterMGKImage(void)
				910	%
				911	*/
				912	ModuleExport unsigned long RegisterMGKImage(void)
				913	{
				914	MagickInfo
				915	*entry;
				916
				917	entry=SetMagickInfo("MGK");
				918	entry->decoder=(DecodeImageHandler *) ReadMGKImage;
				919	entry->encoder=(EncodeImageHandler *) WriteMGKImage;
				920	entry->magick=(IsImageFormatHandler *) IsMGK;
				921	entry->description=ConstantString("MGK");
				922	entry->module=ConstantString("MGK");
				923	(void) RegisterMagickInfo(entry);
				924	return(MagickImageCoderSignature);
				925	}
				926
				927	/*
				928	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				929	% %
				930	% %
				931	% %
				932	% U n r e g i s t e r M G K I m a g e %
				933	% %
				934	% %
				935	% %
				936	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				937	%
				938	% UnregisterMGKImage() removes format registrations made by the
				939	% MGK module from the list of supported formats.
				940	%
				941	% The format of the UnregisterMGKImage method is:
				942	%
				943	% UnregisterMGKImage(void)
				944	%
				945	*/
				946	ModuleExport void UnregisterMGKImage(void)
				947	{
				948	(void) UnregisterMagickInfo("MGK");
				949	}
				950
				951	/*
				952	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				953	% %
				954	% %
				955	% %
				956	% W r i t e M G K I m a g e %
				957	% %
				958	% %
				959	% %
				960	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				961	%
				962	% WriteMGKImage() writes an image to a file in red, green, and blue
				963	% MGK rasterfile format.
				964	%
				965	% The format of the WriteMGKImage method is:
				966	%
				967	% MagickBooleanType WriteMGKImage(const ImageInfo image_info,Image image)
				968	%
				969	% A description of each parameter follows.
				970	%
				971	% o image_info: the image info.
				972	%
				973	% o image: The image.
				974	%
				975	*/
				976	static MagickBooleanType WriteMGKImage(const ImageInfo image_info,Image image)
				977	{
				978	char
				979	buffer[MaxTextExtent];
				980
				981	long
				982	y;
				983
				984	MagickBooleanType
				985	status;
				986
				987	MagickOffsetType
				988	scene;
				989
				990	register const PixelPacket
				991	*p;
				992
				993	register long
				994	x;
				995
				996	register unsigned char
				997	*q;
				998
				999	unsigned char
				1000	*pixels;
				1001
				1002	/*
				1003	Open output image file.
				1004	*/
				1005	assert(image_info != (const ImageInfo *) NULL);
				1006	assert(image_info->signature == MagickSignature);
				1007	assert(image != (Image *) NULL);
				1008	assert(image->signature == MagickSignature);
				1009	if (image->debug != MagickFalse)
				1010	(void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
				1011	status=OpenBlob(image_info,image,WriteBinaryBlobMode,&image->exception);
				1012	if (status == MagickFalse)
				1013	return(status);
				1014	scene=0;
				1015	do
				1016	{
				1017	/*
				1018	Allocate memory for pixels.
				1019	*/
				1020	if (image->colorspace != RGBColorspace)
				1021	(void) SetImageColorspace(image,RGBColorspace);
				1022	pixels=(unsigned char *) AcquireQuantumMemory((size_t) image->columns,
				1023	3ULsizeof(pixels));
				1024	if (pixels == (unsigned char *) NULL)
				1025	ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
				1026	/*
				1027	Initialize raster file header.
				1028	*/
				1029	(void) WriteBlobString(image,"id=mgk\n");
				1030	(void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
				1031	image->columns,image->rows);
				1032	(void) WriteBlobString(image,buffer);
				1033	for (y=0; y < (long) image->rows; y++)
				1034	{
				1035	p=GetVirtualPixels(image,0,y,image->columns,1,&image->exception);
				1036	if (p == (const PixelPacket *) NULL)
				1037	break;
				1038	q=pixels;
				1039	for (x=0; x < (long) image->columns; x++)
				1040	{
				1041	*q++=ScaleQuantumToChar(p->red);
				1042	*q++=ScaleQuantumToChar(p->green);
				1043	*q++=ScaleQuantumToChar(p->blue);
				1044	p++;
				1045	}
				1046	(void) WriteBlob(image,(size_t) (q-pixels),pixels);
				1047	if ((image->previous == (Image *) NULL) &&
				1048	(SetImageProgress(image,SaveImageTag,y,image->rows) == MagickFalse))
				1049	break;
				1050	}
				1051	pixels=(unsigned char *) RelinquishMagickMemory(pixels);
				1052	if (GetNextImageInList(image) == (Image *) NULL)
				1053	break;
				1054	image=SyncNextImageInList(image);
				1055	status=SetImageProgress(image,SaveImagesTag,scene,
				1056	GetImageListLength(image));
				1057	if (status == MagickFalse)
				1058	break;
				1059	scene++;
				1060	} while (image_info->adjoin != MagickFalse);
				1061	(void) CloseBlob(image);
				1062	return(MagickTrue);
				1063	}
				1064	</pre>
				1065	</div>
				1066
				1067	<p>To invoke the custom coder from the command line, use these commands:</p>
				1068
				1069	<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert logo: logo.mgk</span><span class='crtout'></span><span class="crtprompt"> $magick> </span><span class='crtin'>display logo.mgk</span></p>
				1070	<p>We provide the <a href="ftp://ftp.imagemagick.org/pub/ImageMagick/kits/MagickCoderKit-1.0.0.tar.gz">Magick Coder Kit</a> to help you get started writing your own custom coder.</p>
				1071
				1072	</div>
				1073
				1074	<h2><a name="filters"></a>Custom Image Filters</h2>
				1075	<div class="doc-section">
				1076
				1077	<p>ImageMagick provides a convenient mechanism for adding your own custom image processing algorithms. We call these image filters and they are invoked from the command line with the <a href="../www/command-line-options.html#process">-process</a> option or from the MagickCore API method <a href="../www/api/module.html#ExecuteModuleProcess">ExecuteModuleProcess()</a>.</p>
				1078
				1079	<p>Here is a listing of a sample <a href="../www/source/analyze.c">custom image filter</a>. It computes a few statistics such as the pixel brightness and saturation mean and standard-deviation.</p>
				1080
				1081	<div class="viewport">
				1082	<pre class="code">
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1083	#include <stdio.h>
				1084	#include <stdlib.h>
				1085	#include <string.h>
				1086	#include <time.h>
				1087	#include <assert.h>
				1088	#include <math.h>
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1089	#include "magick/MagickCore.h"
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1090
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1091	/*
				1092	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				1093	% %
				1094	% %
				1095	% %
				1096	% a n a l y z e I m a g e %
				1097	% %
				1098	% %
				1099	% %
				1100	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
				1101	%
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1102	% analyzeImage() computes the brightness and saturation mean, standard
				1103	% deviation, kurtosis and skewness and stores these values as attributes
				1104	% of the image.
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1105	%
				1106	% The format of the analyzeImage method is:
				1107	%
				1108	% unsigned long analyzeImage(Image *images,const int argc,
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1109	% char *argv,ExceptionInfo exception)
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1110	%
				1111	% A description of each parameter follows:
				1112	%
				1113	% o image: the address of a structure of type Image.
				1114	%
				1115	% o argc: Specifies a pointer to an integer describing the number of
				1116	% elements in the argument vector.
				1117	%
				1118	% o argv: Specifies a pointer to a text array containing the command line
				1119	% arguments.
				1120	%
				1121	% o exception: return any errors or warnings in this structure.
				1122	%
				1123	*/
				1124	ModuleExport unsigned long analyzeImage(Image **images,const int argc,
				1125	const char *argv,ExceptionInfo exception)
				1126	{
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1127	char
				1128	text[MaxTextExtent];
				1129
				1130	double
				1131	area,
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1132	brightness,
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1133	brightness_mean,
				1134	brightness_standard_deviation,
				1135	brightness_kurtosis,
				1136	brightness_skewness,
				1137	brightness_sum_x,
				1138	brightness_sum_x2,
				1139	brightness_sum_x3,
				1140	brightness_sum_x4,
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1141	hue,
				1142	saturation,
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1143	saturation_mean,
				1144	saturation_standard_deviation,
				1145	saturation_kurtosis,
				1146	saturation_skewness,
				1147	saturation_sum_x,
				1148	saturation_sum_x2,
				1149	saturation_sum_x3,
				1150	saturation_sum_x4;
				1151
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1152	Image
				1153	*image;
				1154
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1155	assert(images != (Image **) NULL);
				1156	assert(images != (Image ) NULL);
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1157	assert((*images)->signature == MagickSignature);
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1158	(void) argc;
				1159	(void) argv;
				1160	image=(*images);
				1161	for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
				1162	{
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1163	CacheView
				1164	*image_view;
				1165
				1166	long
				1167	y;
				1168
				1169	MagickBooleanType
				1170	status;
				1171
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1172	brightness_sum_x=0.0;
				1173	brightness_sum_x2=0.0;
				1174	brightness_sum_x3=0.0;
				1175	brightness_sum_x4=0.0;
				1176	brightness_mean=0.0;
				1177	brightness_standard_deviation=0.0;
				1178	brightness_kurtosis=0.0;
				1179	brightness_skewness=0.0;
				1180	saturation_sum_x=0.0;
				1181	saturation_sum_x2=0.0;
				1182	saturation_sum_x3=0.0;
				1183	saturation_sum_x4=0.0;
				1184	saturation_mean=0.0;
				1185	saturation_standard_deviation=0.0;
				1186	saturation_kurtosis=0.0;
				1187	saturation_skewness=0.0;
				1188	area=0.0;
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1189	status=MagickTrue;
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1190	image_view=AcquireCacheView(image);
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1191	#if defined(MAGICKCORE_OPENMP_SUPPORT)
				1192	#pragma omp parallel for schedule(dynamic,4) shared(status)
				1193	#endif
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1194	for (y=0; y < (long) image->rows; y++)
				1195	{
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1196	register const PixelPacket
				1197	*p;
				1198
				1199	register long
				1200	x;
				1201
				1202	if (status == MagickFalse)
				1203	continue;
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1204	p=GetCacheViewVirtualPixels(image_view,0,y,image->columns,1,exception);
				1205	if (p == (const PixelPacket *) NULL)
cristy	76e378e	2009-12-21 18:20:04 +0000	[diff] [blame]	1206	{
				1207	status=MagickFalse;
				1208	continue;
				1209	}
cristy	3ed852e	2009-09-05 21:47:34 +0000	[diff] [blame]	1210	for (x=0; x < (long) image->columns; x++)
				1211	{
				1212	ConvertRGBToHSB(p->red,p->green,p->blue,&hue,&saturation,&brightness);
				1213	brightness*=QuantumRange;
				1214	brightness_sum_x+=brightness;
				1215	brightness_sum_x2+=brightness*brightness;
				1216	brightness_sum_x3+=brightnessbrightnessbrightness;
				1217	brightness_sum_x4+=brightnessbrightnessbrightness*brightness;
				1218	saturation*=QuantumRange;
				1219	saturation_sum_x+=saturation;
				1220	saturation_sum_x2+=saturation*saturation;
				1221	saturation_sum_x3+=saturationsaturationsaturation;
				1222	saturation_sum_x4+=saturationsaturationsaturation*saturation;
				1223	area++;
				1224	p++;
				1225	}
				1226	}
				1227	image_view=DestroyCacheView(image_view);
				1228	if (area <= 0.0)
				1229	break;
				1230	brightness_mean=brightness_sum_x/area;
				1231	(void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
				1232	(void) SetImageProperty(image,"filter:brightness:mean",text);
				1233	brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
				1234	area*brightness_sum_x/area));
				1235	(void) FormatMagickString(text,MaxTextExtent,"%g",
				1236	brightness_standard_deviation);
				1237	(void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
				1238	if (brightness_standard_deviation != 0)
				1239	brightness_kurtosis=(brightness_sum_x4/area-4.0brightness_mean
				1240	brightness_sum_x3/area+6.0brightness_meanbrightness_mean*
				1241	brightness_sum_x2/area-3.0brightness_meanbrightness_mean*
				1242	brightness_meanbrightness_mean)/(brightness_standard_deviation
				1243	brightness_standard_deviationbrightness_standard_deviation
				1244	brightness_standard_deviation)-3.0;
				1245	(void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
				1246	(void) SetImageProperty(image,"filter:brightness:kurtosis",text);
				1247	if (brightness_standard_deviation != 0)
				1248	brightness_skewness=(brightness_sum_x3/area-3.0brightness_mean
				1249	brightness_sum_x2/area+2.0brightness_meanbrightness_mean*
				1250	brightness_mean)/(brightness_standard_deviation*
				1251	brightness_standard_deviation*brightness_standard_deviation);
				1252	(void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
				1253	(void) SetImageProperty(image,"filter:brightness:skewness",text);
				1254	saturation_mean=saturation_sum_x/area;
				1255	(void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
				1256	(void) SetImageProperty(image,"filter:saturation:mean",text);
				1257	saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
				1258	area*saturation_sum_x/area));
				1259	(void) FormatMagickString(text,MaxTextExtent,"%g",
				1260	saturation_standard_deviation);
				1261	(void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
				1262	if (saturation_standard_deviation != 0)
				1263	saturation_kurtosis=(saturation_sum_x4/area-4.0saturation_mean
				1264	saturation_sum_x3/area+6.0saturation_meansaturation_mean*
				1265	saturation_sum_x2/area-3.0saturation_meansaturation_mean*
				1266	saturation_meansaturation_mean)/(saturation_standard_deviation
				1267	saturation_standard_deviationsaturation_standard_deviation
				1268	saturation_standard_deviation)-3.0;
				1269	(void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
				1270	(void) SetImageProperty(image,"filter:saturation:kurtosis",text);
				1271	if (saturation_standard_deviation != 0)
				1272	saturation_skewness=(saturation_sum_x3/area-3.0saturation_mean
				1273	saturation_sum_x2/area+2.0saturation_meansaturation_mean*
				1274	saturation_mean)/(saturation_standard_deviation*
				1275	saturation_standard_deviation*saturation_standard_deviation);
				1276	(void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
				1277	(void) SetImageProperty(image,"filter:saturation:skewness",text);
				1278	}
				1279	return(MagickImageFilterSignature);
				1280	}
				1281	</pre>
				1282	</div>
				1283
				1284	<p>To invoke the custom filter from the command line, use this command:</p>
				1285
				1286	<p class='crt'><span class="crtprompt"> $magick> </span><span class='crtin'>convert logo: -process analyze -verbose info:</span><span class='crtout'>Image: logo: <br/>
				1287	Format: LOGO (ImageMagick Logo) <br/>
				1288	Class: PseudoClass <br/>
				1289	Geometry: 640x480 <br/>
				1290	... <br/>
				1291	filter:brightness:kurtosis: 8.98864 <br/>
				1292	filter:brightness:mean: 238.096 <br/>
				1293	filter:brightness:skewness: -3.04519 <br/>
				1294	filter:brightness:standard-deviation: 46.3286 <br/>
				1295	filter:saturation:kurtosis: 5.9137 <br/>
				1296	filter:saturation:mean: 23.4635 <br/>
				1297	filter:saturation:skewness: 2.71874 <br/>
				1298	filter:saturation:standard-deviation: 64.7734</span></p>
				1299
				1300	<p>We provide the <a href="ftp://ftp.imagemagick.org/pub/ImageMagick/kits/MagickFilterKit-1.0.0.tar.gz">Magick Filter Kit</a> to help you get started writing your own custom image filter.</p>
				1301
				1302	</div>
cristy	f3bb478	2009-09-08 13:10:04 +0000	[diff] [blame]	1303
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cristy	16ff93c	2010-01-13 23:18:07 +0000	[diff] [blame^]	1311	<a href="http://studio.webbyland.com/ImageMagick/MagickStudio/scripts/MagickStudio.cgi">Studio</a>
cristy	f3bb478	2009-09-08 13:10:04 +0000	[diff] [blame]	1312	</span>
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cristy	16af1cb	2009-12-11 21:38:29 +0000	[diff] [blame]	1316	<span id="footer-west">© 1999-2010 ImageMagick Studio LLC</span>
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