These examples of ImageMagick usage illustrate what you can do with an image from the command line, a program interface, or script. You can generate this image yourself with this PerlMagick script, examples.pl.
9 | 10 |![[ImageMagick Examples]](<?php echo $_SESSION['RelativePath']?>/../image/examples.jpg)
There are no notices at this time.
9 |9 | 10 |
As the organization overseeing the open-source ImageMagick software distribution, ImageMagick Studio LLC does not collect any personal identifier information (PII). In addition to the organization, the ImageMagick software distribution does not collect PII either.
9 | 10 |These examples of ImageMagick usage illustrate what you can do with an image from the command line, a program interface, or script. You can generate this image yourself with this PerlMagick script, examples.pl.
9 | 10 |Learn how to cite ImageMagick in your work. Choose from these citation formats:
9 | 10 |ImageMagick Studio LLC. (2024). ImageMagick. Retrieved from https://imagemagick.org12 | 13 |
1. ImageMagick Studio LLC. ImageMagick [Internet]. 2024. Available from: https://imagemagick.org15 | 16 |
18 |ImageMagick Studio LLC, 2024. ImageMagick, Available at: https://imagemagick.org.
@software{imagemagick,
20 | author = {{ImageMagick Studio LLC}},
21 | title = {ImageMagick},
22 | url = {https://imagemagick.org},
23 | version = {7.1.1},
24 | date = {2024-01-04},
25 | }
26 |
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/Magick++/Cache.fig:
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1 | #FIG 3.2
2 | Landscape
3 | Center
4 | Inches
5 | Letter
6 | 100.00
7 | Single
8 | 0
9 | 1200 2
10 | 1 3 0 3 4 4 0 0 20 0.000 1 0.0000 2715 3030 31 31 2715 3030 2745 3037
11 | 2 1 0 1 0 7 0 0 -1 0.000 0 0 -1 1 0 2
12 | 1 1 1.00 60.00 120.00
13 | 1200 3300 1200 2100
14 | 2 1 0 1 0 7 0 0 -1 0.000 0 0 -1 1 0 2
15 | 1 1 1.00 60.00 120.00
16 | 2925 1875 1500 1875
17 | 2 1 0 1 0 7 0 0 -1 0.000 0 0 -1 1 0 2
18 | 1 1 1.00 60.00 120.00
19 | 3825 1875 4800 1875
20 | 2 1 0 1 0 7 0 0 -1 0.000 0 0 -1 1 0 2
21 | 1 1 1.00 60.00 120.00
22 | 1200 3600 1200 4800
23 | 2 2 0 1 0 6 9 0 30 0.000 0 0 -1 0 0 5
24 | 2325 2700 4125 2700 4125 3825 2325 3825 2325 2700
25 | 2 2 0 1 0 2 10 0 30 0.000 0 0 7 0 0 5
26 | 1500 2100 4800 2100 4800 4800 1500 4800 1500 2100
27 | 2 2 0 1 7 7 11 0 20 0.000 0 0 -1 0 0 5
28 | 900 1500 5100 1500 5100 5100 900 5100 900 1500
29 | 4 1 0 0 0 16 12 0.0000 4 180 810 3375 1950 columns()\001
30 | 4 2 0 0 0 16 12 0.0000 4 180 510 1500 3525 rows()\001
31 | 4 0 0 0 0 16 12 0.0000 4 165 255 1575 2325 0,0\001
32 | 4 1 0 0 0 16 12 0.0000 4 180 795 3375 2625 columns_\001
33 | 4 1 0 0 0 16 12 0.0000 4 135 225 2325 2625 x,y\001
34 | 4 2 0 0 0 16 12 0.0000 4 135 495 2250 3300 rows_\001
35 | 4 0 0 0 0 16 12 0.0000 4 135 405 2730 3232 Pixel\001
36 |
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/Magick++/thumbnail-anatomy-plain.fig:
--------------------------------------------------------------------------------
1 | #FIG 3.2
2 | Portrait
3 | Center
4 | Inches
5 | Letter
6 | 100.00
7 | Single
8 | -3
9 | 1200 2
10 | 2 1 0 1 -1 7 0 0 -1 0.000 0 0 -1 1 0 2
11 | 1 1 1.00 60.00 120.00
12 | 3825 1200 3600 1875
13 | 2 1 0 1 -1 7 0 0 -1 0.000 0 0 -1 1 0 2
14 | 1 1 1.00 60.00 120.00
15 | 4950 1200 4575 2100
16 | 2 1 0 1 -1 7 0 0 -1 0.000 0 0 -1 1 0 2
17 | 1 1 1.00 60.00 120.00
18 | 6000 3900 4950 4350
19 | 2 5 0 1 -1 -1 2 0 -1 0.000 0 0 -1 0 0 5
20 | 0 thumbnail-sample-plain.jpg
21 | 2700 1800 5850 1800 5850 4935 2700 4935 2700 1800
22 | 2 1 0 1 -1 7 0 0 -1 0.000 0 0 -1 1 0 2
23 | 1 1 1.00 60.00 120.00
24 | 6000 3075 5250 3375
25 | 2 2 0 1 0 7 10 0 -1 0.000 0 0 -1 0 0 5
26 | 1800 600 6900 600 6900 6000 1800 6000 1800 600
27 | 4 1 -1 0 0 16 14 0.0000 4 165 1875 4275 5250 PLAIN THUMBNAIL\001
28 | 4 1 -1 0 0 16 10 0.0000 4 120 480 3825 975 Thumb\001
29 | 4 1 -1 0 0 16 10 0.0000 4 120 465 3825 1155 Border\001
30 | 4 1 -1 0 0 16 10 0.0000 4 135 435 4950 1140 Image\001
31 | 4 1 -1 0 0 16 10 0.0000 4 120 480 4950 975 Thumb\001
32 | 4 1 -1 0 0 16 10 0.0000 4 120 570 6300 3180 Shadow\001
33 | 4 1 -1 0 0 16 10 0.0000 4 120 480 6300 3000 Thumb\001
34 | 4 1 -1 0 0 16 10 0.0000 4 120 390 6300 4005 Label\001
35 | 4 1 -1 0 0 16 10 0.0000 4 120 480 6300 3825 Thumb\001
36 |
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/Magick++/ImageDesign.html:
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1 |
2 |
3 |
4 |
5 |
6 | 
ImageMagick Studio LLC is a limited liability corporation based in the United States of America. All of our products are developed via online collaboration in public forums and distributed from a central server within the U.S. Therefore, U.S. export laws and regulations apply to our distributions and remain in force as products and technology are re-exported to different parties and places around the world. Information on export control classifications and associated restrictions may be required for exporting, re-exporting, record keeping, bundling/embedding of ImageMagick products, encryption reporting, and shipping documentation. More information on U.S. Export Regulations can be found at the U. S. Bureau of Industry and Security.
9 | 10 |The ImageMagick software distribution is classified as ECCN 5D002. However, ImageMagick Studio LLC makes no warranty or representation that this classification is accurate, current, or complete. ImageMagick is exported under the TSU exception in EAR 740.13(e) which applies to software containing or designed for use with encryption software that is publicly available as open source. TSU further provides that Posting encryption source code and corresponding object code on the Internet (e.g., FTP or World Wide Web site) where it may be downloaded by anyone neither establishes "knowledge" of a prohibited export or reexport for purposes of this paragraph, nor triggers any "red flags" necessitating the affirmative duty to inquire[...]. It is your obligation as the exporter to comply with the current applicable requirements of United States export rules and regulations.
11 |This document describes the requirements and instructions to build ImageMagick for Windows on your own machine.
9 | 10 |To build ImageMagick with Visual Studio the following components should be installed:
19 | 20 |Naming of these components might differ between version of Visual Studio. The example above use the Visual Studio 2017 names.
28 | 29 |The ImageMagick library is built with a number of third party libraries. Run CloneRepositories.IM7.cmd to clone 31 | these libraries and the ImageMagick library. To clone the legacy ImageMagick 6 library and it's dependencies 32 | run CloneRepositories.IM6.cmd.
33 | 34 |One of the folders in this project is called Configure. This folder contains the solution file Configure.sln 36 | for the latest 2022 version of Visual Studio, and Configure.2017.sln for older versions. Open one of those and 37 | start a Release build of the project. This will create a file called Configure.exe in the folder. Running this 38 | program will start a Wizard that allows configuration of ImageMagick and its individual components.
39 | 40 |Depending on which options where chosen when running configure.exe one of the following solutions will be created in the root of the repository:
42 | 43 |Open the solution to start building ImageMagick. The binaries will be created in the Output\bin folder.
50 |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 or large image sequences. Start up the pixel cache server on one or more hosts. 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.
9 |For really large images or large image sequences, or if there is limited resources on your host, you can utilize a distributed pixel cache on one or more remote hosts. To get started, first set your shared secret in the policy.xml security policy configuration file:
10 |11 | <policy domain="cache" name="shared-secret" value="passphrase" stealth="true"/>12 | 13 |
Here we create two distributed pixel caches and utilize them from our desktop:
14 |magick -distribute-cache 6668 & # start on 192.168.100.50 15 | magick -distribute-cache 6668 & # start on 192.168.100.51 16 | magick -limit memory 1GiB -limit map 2GiB -limit disk 4GiB \ 17 | -define registry:cache:hosts=192.168.100.50:6668,192.168.100.51:6668 \ 18 | myhugeimage.jpg -sharpen 5x2 myhugeimage.png19 |
For large image sequences, the servers are contacted in a round-robin fashion to distribute the load over multiple distributed pixel caches (assuming you have a host list rather than a single host). In our example, some modest resources are available on the desktop as defined by the -limit option. For smaller images, they are allocated on the desktop up to the specified limits.
20 |Your image processing tasks are likely to perform slower when utilizing a distributed pixel cache due to shuffling pixels between the client and the server over a network. Algorithms that access virtual pixels (e.g. -sharpen) are noticeably slower, up to 3 times slower, than algorithms that only access authentic pixels (e.g. -negate) due to increased network traffic.
21 |A client can only contact a compatible distributed pixel cache server. Compatibility requires the same ImageMagick library interface, quantum depth, HDRI status, OS word size, endianness, and passphrase. The distributed pixel cache checks these attributes and throws an exception if these requirements are not met.
22 |A challenging release plan has been developed for Magick++. What actually gets accomplished depends on the level of support from users and developers. Volunteers are needed. In particular, work on the CORBA/COM IDL-base API may proceed in parallel with other development. The following is the tentative development and release plan (step 1.0 is complete).
13 |1.0 API for operating on individual images and STL containers of images
14 |This version supports all ImageMagick API operations which operate on a single image as well as providing STL container support for operating on multiple images (on any STL compatible container which supports a forward input iterator).15 |
STL is used as the framework in which to store images. Template functions (e.g. montage) are provided to build the image lists required by ImageMagick and then invoke the list-oriented ImageMagick API. STL is quite powerful yet easy to use. At this stage Magick++ has matched what is currently available/possible using the PerlMagick API due to leveraging the power of STL.16 |
2.0 CORBA and/or COM IDL based client API with server implementation for executing image processing operations on a remote (or local) computer.
17 |This version provides an IDL-based API. A C++ wrapper API compatible with that developed for release 2.0 is available for use by clients. Client wrappers may also be developed for other languages (e.g. Java). COM and CORBA servers are provided which are implemented in terms of the Magick++ API in order to satisfy client requests (which may run a different operating system than the server).18 |
3.0 Integration of IDL-based API with an existing open source work-queing system in order to load-share image processing tasks and the image frame and file level across a large number of machines.
19 |This version is the culmination of the effort. By intelligently spreading work over many machines, the performance of ImageMagick is magnified. In order for this to be a success algorithms for efficient transfer of image data must be developed. Algorithms that take into account processor afinity and the CPU vs I/O tradeoff for the task to be performed must be developed. At this point in time, the queuing system to be employed has not been identified.20 | 21 | 22 | 23 | -------------------------------------------------------------------------------- /source/piechart.svg: -------------------------------------------------------------------------------- 1 | 2 | 4 | 33 | -------------------------------------------------------------------------------- /image/convex-hull.php: -------------------------------------------------------------------------------- 1 |
The convex hull is the is the smallest area convex polygon containing the set of points inside it. The convex hull may be visualized as the shape enclosed by a rubber band stretched around the set of points.
2 | 3 |The convex-hull string format returns a list of x,y coordinates of the vertices of the convex-hull polygon containing all the non-black pixels within it.
4 | 5 |6 | magick [-fuzz XXX%] [-define convex-hull:background-color] -format "%[convex-hull]" info: 7 |8 | 9 |
where the string format is sensitive to an optional -fuzz value and to an optional background color specified by the define. The command above will find the background color automatically according to the fuzz value unless the background color is defined. The fuzz value defaults to 0 when not specified.
For example, consider the following white rectangle on a black background:
12 | 13 |![[Convex Hull]](<?php echo $_SESSION['RelativePath']?>/../image/convex-hull.png)
The convex hull set of points may be computed as:
16 | 17 |magick rect.png -format "%[convex-hull]" info: 18 | 190,121 193,122 281,154 377,189 378,190 377,193 345,281 310,377 309,378 306,377 218,345 122,310 121,309 122,306 154,218 189,122 190,121 19 |20 | 21 |
The convex hull may also be drawn as a polygon (filled or unfilled) using -draw as follows:
magick rect.png -set option:hull "%[convex-hull]" -fill none -stroke red -strokewidth 1 -draw "polygon %[hull]" blocks_hull.png24 | 25 |
Here is an example using a non-convex shaped image on a black background:
26 | 27 |![[Convex Hull Blocks]](<?php echo $_SESSION['RelativePath']?>/../image/convex-hull-blocks.png)
magick blocks_black.png -set option:hull "%[convex-hull]" -fill none -stroke red -strokewidth 1 -draw "polygon %[hull]" blocks_hull.png30 | 31 |
![[Convex Hull Blocks Closure]](<?php echo $_SESSION['RelativePath']?>/../image/convex-hull-blocks-closure.png)
Finally, here is an example with a non-constant, non-black background using -fuzz to determine the background color:
34 | 35 |![[Convex Hull Barn]](<?php echo $_SESSION['RelativePath']?>/../image/convex-hull-barn.png)
magick barn_rot20.png -fuzz 30% -set option:hull "%[convex-hull]" -fill none -stroke red -strokewidth 1 -draw "polygon %[hull]" barn_rot20_hull.png38 | 39 |
![[Convex Hull Barn Closure]](<?php echo $_SESSION['RelativePath']?>/../image/convex-hull-barn-closure.png)
The Magick::Image methods annotate, draw, label, and the template function montageImages support special format characters contained in the argument text. These format characters work similar to C's printf. Whenever a format character appears in the text, it is replaced with the equivalent attribute text. The available format characters are shown in the following table.
13 |Format Characters
15 ||
21 | Format Character |
22 |
23 | Description |
|
26 | %b |
27 |
28 | file size |
|
31 | %d |
32 |
33 | directory |
|
36 | %e |
37 |
38 | filename extension |
|
41 | %f |
42 |
43 | filename |
|
46 | %h |
47 |
48 | height |
|
51 | %m |
52 |
53 | magick (e.g GIF) |
|
56 | %p |
57 |
58 | page number |
|
61 | %s |
62 |
63 | scene number |
|
66 | %t |
67 |
68 | top of filename |
|
71 | %w |
72 |
73 | width |
|
76 | %x |
77 |
78 | x resolution |
|
81 | %y |
82 |
83 | y resolution |
|
86 | \n |
87 |
88 | newline |
|
91 | \r |
92 |
93 | carriage return |
The Voluntary Product Accessibility Template (VPAT) is a document that describes how an information technology (IT) product, such as software, hardware, or web-based applications, meets the accessibility standards defined by Section 508 of the Rehabilitation Act. This VPAT describes the accessibility features of the ImageMagick open-source project.
10 |This VPAT is based on a review of the ImageMagick project documentation, including the project website and the software documentation.
17 | 18 |ImageMagick is a command-line utility for creating, editing, and converting images. The software can be used with screen readers and other assistive technologies to access the command-line interface. However, the interface is not optimized for use with assistive technologies, and some users may find it difficult to use without significant customization.
21 | 22 |ImageMagick does not have any web-based features, so this section does not apply.
25 | 26 |ImageMagick does not include any telecommunications features, so this section does not apply.
29 | 30 |ImageMagick does not include any video or multimedia features, so this section does not apply.
33 | 34 |Section 1194.25 - Self-Contained, Closed Products
35 | 36 |ImageMagick is an open-source command-line utility and does not meet the requirements of this section.
37 | 38 |ImageMagick is a command-line utility and does not include a graphical user interface (GUI) that could be used with assistive technologies. This section does not apply.
41 | 42 |ImageMagick does not include any functional performance criteria.
45 | 46 |The ImageMagick project provides online documentation in HTML format, which is accessible using screen readers and other assistive technologies. The documentation includes installation instructions, command-line reference, and other resources. However, some of the documentation may be technical and difficult for non-technical users to understand. The project does not offer any support services for users with disabilities.
49 | 50 |ImageMagick is an open-source command-line utility that provides basic accessibility features for users who rely on assistive technologies. However, the software is not optimized for use with assistive technologies and may require significant customization to be accessible to all users. The project provides accessible online documentation, but may not be suitable for non-technical users.
53 | 54 | 55 |High dynamic-range imaging (HDRI) 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. The HDR imaging approach includes:
9 | 10 |ImageMagick supports the Jzazbc colorspace, for applications that require wide color gamut and high dynamic range.
18 | 19 |By default, image pixels in ImageMagick version 7 are stored in a floating-point representation that range from 0 to the quantum depth, which is typically 16-bits (Q16). With HDRI enabled, the pixels can include negative values as well as values that exceed the quantum depth. A majority of digital image formats do not support HDRI, and for those images any pixels outside the quantum range are clamped before they are stored.
22 | 23 |The most promising HDR image format is EXR. You must have the OpenEXR delegate library installed to read or write this format. Other HDR formats include TIFF 48-bit integer and 96-bit float formats, HDR, PFM, and ImageMagick's own MIFF format.
24 | 25 |To disable the HDRI version of ImageMagick, use this Linux/Linux command:
26 | 27 |./configure --disable-hdri 28 |29 | 30 |
Under Windows, follow the instructions (straightforward for a non-programmer) in a one hour process to build and configure your own executables: Install from Windows Source.
31 | 32 |To verify HDRI is properly configured, look for "HDRI" as a feature:
33 | 34 |magick identify -version 35 | Features: HDRI 36 |37 | 38 |
With HDRI enabled, you can now create images with a much wider dynamic range, allowing for more vivid colors and better contrast. It ensures that HDR content can be displayed accurately on compatible devices while maintaining backward compatibility with SDR displays. In this example, you can store the difference between a standard dynamic range (SDR) image and its high dynamic range (HDR) counterpart. Essentially, a gain map captures the additional brightness and color information that HDR provides over SDR:
39 | 40 |magick -define uhdr:hdr-color-gamut=bt709 -define uhdr:hdr-color-transfer=hlg \ 41 | \( img_sdr.tif -depth 8 \) \( img_hdr.tif -depth 16 \) uhdr:ultrahdr.jpg 42 |43 |
Many of ImageMagick's internal algorithms are threaded to take advantage of speed-ups offered by the multicore processor chips and OpenMP. OpenMP, is an API specification for parallel programming. If your compiler supports OpenMP (e.g. gcc, Visual Studio 2005) directives, ImageMagick automatically includes support. To verify, look for the OpenMP feature of ImageMagick with this command:
9 |$ magick identify -version 10 | Version: ImageMagick 7.0.10-50 2021-01-04 Q16 https://imagemagick.org 11 | Copyright: © 1999-2021 ImageMagick Studio LLC 12 | Features: OpenMP(4.5)13 |
With OpenMP enabled, most ImageMagick algorithms execute on all the cores on your system in parallel. ImageMagick typically divides the work so that each thread processes 64 rows of pixels. As rows are completed, OpenMP assigns more chunks of pixel rows to each thread until the algorithm completes. For example, if you have a quad-core system, and attempt to resize an image, the resizing takes place on 4 cores (8 if hyperthreading is enabled).
14 |You can further increase performance by reducing lock contention with the tcmalloc memory allocation library. To enable, add --with-tcmalloc to the configure command-line when you build ImageMagick.
15 |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 the 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 are the most efficient in your environment. Here is an example benchmark for threads 1-8:
17 | 18 |$ magick -bench 40 model.png -sharpen 0x1 null: 19 | Performance[1]: 40i 0.712ips 1.000e 14.000u 0:14.040 20 | Performance[2]: 40i 1.362ips 0.657e 14.550u 0:07.340 21 | Performance[3]: 40i 2.033ips 0.741e 14.530u 0:04.920 22 | Performance[4]: 40i 2.667ips 0.789e 14.590u 0:03.750 23 | Performance[5]: 40i 3.236ips 0.820e 14.970u 0:03.090 24 | Performance[6]: 40i 3.802ips 0.842e 15.280u 0:02.630 25 | Performance[7]: 40i 4.274ips 0.857e 15.540u 0:02.340 26 | Performance[8]: 40i 4.831ips 0.872e 15.680u 0:02.07027 |
Better performance correlates with higher values of IPS (iterations-per-second). In our example, 8 cores are optimal. However, in certain cases it might be optimal to set the number of threads to 1 (e.g. -limit thread 1) or to disable OpenMP completely. To disable this feature, add --disable-openmp to your configure script command line then rebuild and re-install ImageMagick.
28 |ImageMagick's JPEG-2000 image formats, JP2 and JPC, accept a plethora of encoding options as detailed below. As an example, suppose you are interested in these options:
10 | 11 |Use this command to convert a JPEG-2000 image to the PNG image format:
19 | 20 |magick wizard.jp2 wizard.png21 | 22 |
Let's convert a JPEG image to a lossless JPEG-2000 image:
23 | 24 |magick wizard.jpg -quality 0 wizard.jp225 | 26 |
Here we extract an area from the image:
27 | 28 |magick 'wizard.jp2[640x480+0+0]' wizard.png29 | 30 |
Extract a particular tile from the image:
31 | 32 |magick 'wizard.jp2[2]' wizard.png33 | 34 |
Specify a subsampling factor:
35 | 36 |magick wizard.png -colorspace YUV -sampling-factor 2:2 wizard.jp237 | 38 |
Save a tiled JPEG-2000 image:
39 | 40 |magick wizard.png 'wizard.png[512x512]'41 | 42 |
Write a digital Cinema 4K profile compliant codestream:
43 | 44 |magick wizard.png -resize 4096x2160! -depth 12 wizard.jp245 | 46 |
Here is a complete list of JPEG-2000 decoding options:
47 | 48 || jp2:quality-layers=x | 52 |set the maximum number of quality layers to decode. | 53 |
| jp2:reduce-factor=x | 56 |set the number of highest resolution levels to be discarded. | 57 |
Here is a complete list of JPEG-2000 encoding options:
61 | 62 || jp2:number-resolutions=x | 66 |number of resolutions to encode. | 67 |
| jp2:quality=x,x,... | 70 |set the quality layer PSNR, given in dB. The order is from left to right in ascending order. The default is a single lossless quality layer. | 71 |
| jp2:rate=x,x,... | 74 |the compression ratio values. Each value is a factor of compression, thus 20 means 20 times compressed. The order is from left to right in descending order. A final lossless quality layer is signified by the value 1. The default is a single lossless quality layer. | 75 |
| jp2:progression-order=x | 78 |choose from LRCP, RLCP, RPCL, PCRL or CPRL. | 79 |
ImageMagick source and binary distributions are available from a variety of FTP and Web mirrors around the world listed below. ImageMagick stable and development source releases are also available from Git. Before you download, you may want to review recent changes to the ImageMagick distribution. The authoritative source code repository is https://github.com/ImageMagick.
9 |The latest release of ImageMagick is version .
10 |If you want to add a new mirror, please contact us.
38 |Use contrast limited adaptive histogram equalization (AHE) to improve contrast in images. Ordinary histogram equalization computes a global equalization whereas an adaptive method computes several histograms, each corresponding to a distinct section of the image, and uses them to redistribute the lightness values of the image. It is suitable for improving the local contrast and enhancing the definitions of edges in each region of an image. A variant of adaptive histogram equalization, contrast limited adaptive histogram equalization (CLAHE) limits AHE's tendency to overamplify noise in relatively homogeneous regions of an image.
9 |CLAHE is supported as of ImageMagick 7.0.8-24 with the -clahe option:
10 | 13 |The image is divided into tiles of width and height pixels. Append % to define the width and height as percentages of the image's dimensions. The tile size should be larger than the size of features to be preserved and respects the aspect ratio of the image. Add ! to force an exact tile width and height. number-bins is the number of histogram bins per tile (min 2, max 65536). The number of histogram bins should be smaller than the number of pixels in a single tile. clip-limit is the contrast limit for localized changes in contrast. A clip-limit of 2 to 3 is a good starting place (e.g. -clahe 50x50%+128+3). Very large values will let the histogram equalization do whatever it wants to do, that is result in maximal local contrast. The value 1 will result in the original image. Note, if the number of bins and the clip-limit are omitted, they default to 128 and no clipping respectively.
14 |To visualize the benefits of CLAHE, we have a low contrast image of mountains:
15 |16 |
18 | We can improve the image with global histogram equalization:
20 |
22 | We can further improve the image with the contrast limited adaptive histogram equalization image processing technique:
24 |
26 | The latter image was produced with this command:
28 |magick mountains.jpg -clahe 25x25%+128+3 mountains-clahe.jpg29 |
The 25x25% argument divides the image into 16 tiles to perform local contrast enhancement. The image dimensions are 1500x1000 so the tiles are exactly 375x250 pixels each. Rather than a percentage, you can specify the tile dimensions directly with 375x250.
30 |For tile sizes that do not divide evenly into the image dimensions, CLAHE utilizes virtual pixels, as such the results can vary slightly based on your chosen virtual pixel method. For example,
31 |magick mountains.jpg -virtual-pixel mirror -clahe 300x300+128+3! mountains-clahe.jpg32 |
Notice the !. That forces the tile size to exactly 300x300 pixels, whereas without the !, the tile size respects the aspect ratio of the image and results in tile dimensions of 300x200.
33 | 34 |The CoderInfo class provides the means to provide information regarding ImageMagick support for an image format (designated by a magick string). It may be used to provide support for a specific named format (provided as an argument to the constructor), or as an element of a container when format support is queried using the coderInfoList() templated function.
13 |The following code fragment illustrates how CoderInfo may be used.
14 |
15 | CoderInfo info("GIF");
16 | cout < info->name() << ": (" << info->description() << ") : ";
17 | cout << "Readable = ";
18 | if ( info->isReadable() )
19 | cout << "true";
20 | else
21 | cout << "false";
22 | cout << ", ";
23 | cout << "Writable = ";
24 | if ( info->isWritable() )
25 | cout << "true";
26 | else
27 | cout << "false";
28 | cout << ", ";
29 | cout << "Multiframe = ";
30 | if ( info->isMultiframe() )
31 | cout << "true";
32 | else
33 | cout << "false";
34 | cout << endl;
35 |
36 | The methods available in the CoderInfo class are shown in the following table:
37 |CoderInfo Methods
39 ||
42 | Method |
43 |
44 | Returns |
45 |
46 | Signature |
47 |
48 | Description |
| 51 | | 52 |53 | |
54 | void |
55 |
56 | Construct object corresponding to named format (e.g. "GIF"). An exception is thrown if the format is not supported. |
| 59 | | 60 |
61 | std::string |
62 |
63 | void |
64 |
65 | Format name (e.g. "GIF"). |
| 68 | | 69 |
70 | std::string |
71 |
72 | void |
73 |
74 | Format description (e.g. "CompuServe graphics interchange format"). |
| 77 | | 78 |
79 | bool |
80 |
81 | void |
82 |
83 | Format is readable. |
| 86 | | 87 |
88 | bool |
89 |
90 | void |
91 |
92 | Format is writeable. |
| 95 | | 96 |
97 | bool |
98 |
99 | void |
100 |
101 | Format supports multiple frames. |
The TypeMetric class provides the means to pass data from the Image class's TypeMetric method to the user. It provides information regarding font metrics such as ascent, descent, text width, text height, and maximum horizontal advance. The units of these font metrics are in pixels, and that the metrics are dependent on the current Image font (default Ghostscript's "Helvetica"), pointsize (default 12 points), and x/y resolution (default 72 DPI) settings.
13 |The pixel units may be converted to points (the standard resolution-independent measure used by the typesetting industry) via the following equation:
14 |15 | size_points = (size_pixels * 72)/resolution 16 |17 |
where resolution is in dots-per-inch (DPI). This means that at the default image resolution, there is one pixel per point.
18 |Note that a font's pointsize is only a first-order approximation of the font height (ascender + descender) in points. The relationship between the specified pointsize and the rendered font height is determined by the font designer.
19 |See FreeType Glyph Conventions for a detailed description of font metrics related issues.
20 |The methods available in the TypeMetric class are shown in the following table:
21 |TypeMetric Methods
22 ||
25 | Method |
26 |
27 | Returns |
28 |
29 | Units |
30 |
31 | Signature |
32 |
33 | Description |
| 36 | | 37 |
38 | double |
39 |
40 | Pixels |
41 |
42 | void |
43 |
44 | Returns the distance in pixels from the text baseline to the highest/upper grid coordinate used to place an outline point. Always a positive value. |
| 47 | | 48 |
49 | double |
50 |
51 | Pixels |
52 |
53 | void |
54 |
55 | Returns the distance in pixels from the baseline to the lowest grid coordinate used to place an outline point. Always a negative value. |
| 58 | | 59 |
60 | double |
61 |
62 | Pixels |
63 |
64 | void |
65 |
66 | Returns text width in pixels. |
| 69 | | 70 |
71 | double |
72 |
73 | Pixels |
74 |
75 | void |
76 |
77 | Returns text height in pixels. |
| 80 | | 81 |
82 | double |
83 |
84 | Pixels |
85 |
86 | void |
87 |
88 | Returns the maximum horizontal advance (advance from the beginning of a character to the beginning of the next character) in pixels. |
Encipher an Image • Decipher an Image • Encipher and Decipher Caveats
9 | 10 |Most images, by design, are made to be viewed often and by many people. Web images, for example, may be viewed hundreds of times a day by a multitude of visitors. However, in some cases, you may want to keep a particular image private so that only you or perhaps a select group of your friends or web visitors can view it. ImageMagick permits you to scramble your images such that unless someone knows your passphrase, they will be unable to view the original content.
11 | 12 |You could use an enciphering utility to scramble your image but they typically scramble the entire file making it unrecognizable as an image format. With ImageMagick, only the pixels are scrambled. The scrambled image continues to be recognized as an image and will even display in your web page. However, the content appears as gibberish, nothing like the original content.
13 | 14 |Use the -encipher option to scramble your image so that it is unrecognizable. The option requires a filename that contains your passphrase. In this example we scramble an image and save it in the PNG format:
17 | 18 |magick rose.jpg -encipher passphrase.txt rose.png19 | 20 |
Here we encipher an image using another image as the passphrase:
21 | 22 |magick rose.jpg -encipher smiley.gif rose.png23 | 24 |
Use the -decipher option to unscramble your image so that it is recognizable once again. The option requires a filename that contains your passphrase. In this example we unscramble an image and save it in the JPEG format:
27 | 28 |magick rose.png -decipher passphrase.txt rose.jpg29 | 30 |
Some formats do not support enciphered pixels-- the JPEG or GIF format, for 33 | example. To ensure your image format is supported, encipher a test image and 34 | verify you can restore its original content before you encipher any 35 | additional images in that format.
36 | 37 |The image format may only support 8-bit and RGB (TrueColor). As such you may 38 | like to include the options "-depth 8 -type TrueColor" before the output 39 | filename.
40 | 41 |The passphrase can be any combinations of letters and symbols. It should 42 | be a minimum of 12 character combinations to help ensure your image remains 43 | private. Also make sure your passphrase file permissions prevent others from 44 | reading it otherwise unintended users may be able to view the original image 45 | content.
46 | 47 |You can only restore the original image content if you know your 48 | passphrase. If you lose or forget it, your original image content is lost 49 | forever.
50 | 51 |ImageMagick only scrambles the image pixels. The image metadata remains 52 | untouched and readable by anyone with access to the image file.
53 | 54 |ImageMagick uses the AES 56 | cipher in Counter mode. We use the first half of your passphrase to derive the nonce. The second half is the cipher key. When used correctly, AES-CTR provides a high level of confidentiality. To avoid information leaks, you must use a fresh passphrase for each image your encrypt.
57 | 58 |Currently only ImageMagick can restore your enciphered image content. We 59 | use a standard cipher and mode so other vendors could support enciphered image content.
60 | 61 |Some small practical examples of image enciphering can be found in IM 62 | Examples Encrypting Image Data.
64 | 65 |The Quantum structure is used to represent pixels in ImageMagick. ImageMagick may be compiled to support 32 or 64 bit pixels. The size of Quantum is controlled by the value of the QuantumDepth define. The default is 64 bit pixels, which provide the best accuracy. If memory consumption must be minimized, or processing time must be minimized, then ImageMagick may be compiled with QuantumDepth=8. The following table shows the relationship between QuantumDepth, the type of Quantum, and the overall Quantum size.
13 |Effect Of QuantumDepth Values
15 ||
22 | QuantumDepth |
23 |
24 | Quantum Type |
25 |
26 | Quantum Size |
|
29 | 8 |
30 |
31 | unsigned char |
32 |
33 | 32 bits |
|
36 | 16 |
37 |
38 | unsigned short |
39 |
40 | 64 bits |
The members of the Quantum structure, and their interpretation, are shown in the following table:
42 |Quantum Pixel Layout
44 ||
53 | Member |
54 |
55 | Type |
56 |
57 | Interpretation | ||
| 60 | | 61 |62 | | 63 |64 | | ||
|
67 | red |
68 |
69 | Quantum |
70 |
71 | Red |
72 |
73 | Red |
74 |
75 | Cyan |
|
78 | green |
79 |
80 | Quantum |
81 |
82 | Green |
83 |
84 | Green |
85 |
86 | Magenta |
|
89 | blue |
90 |
91 | Quantum |
92 |
93 | Blue |
94 |
95 | Blue |
96 |
97 | Yellow |
|
100 | alpha |
101 |
102 | Quantum |
103 |
104 | Ignored |
105 |
106 | Alpha |
107 |
108 | Ignored |
ImageMagick has built-in support for some OpenCL accelerated operations. However, there are some conditions for its operation. These requirements are listed below.
9 | 10 |blur 25 | contrast 26 | charcoal 27 | function 28 | grayscale 29 | motion-blur 30 | resize31 | The following operators are OpenCL accelerated as well, but they require alpha channel to be enabled, e.g. magick sample.jpg -alpha on -despeckle null:. 32 |
despeckle 33 | equalize 34 | modulate35 |
When some of the OpenCL accelerated operators are invoked for the first time and all the conditions above are met, ImageMagick conducts a series of tests to configure the OpenCL environment according to the system hardware; therefore, it is normal to experience a higher latency the first time you use an accelerated option. The OpenCL kernels are embedded inside ImageMagick in source format. During the initial setup, ImageMagick discovers all the available OpenCL devices and compiles the kernels for each of these targets. ImageMagick also runs several performance tests internally to determine the preferred device to use. The compiled kernel code and the performance test results are stored into the cache directory so that the data can be reused by subsequent invocations of the OpenCL path. By default, the OpenCL cached data is stored in $HOME/.cache/ImageMagick on Linux and on MacOSX or in %LOCALAPPDATA%\ImageMagick on Windows. To run these tests for the first time, use the command below:
41 |MAGICK_OCL_DEVICE=true magick sample.jpg -blur 0x5 null:42 |
On Windows the MAGICK_OCL_DEVICE=true part should be removed and the command set MAGICK_OCL_DEVICE=true should be executed before executing the command above to enable OpenCL operations.
43 |To change the cache directory, set the MAGICK_OPENCL_CACHE_DIR environment variable. ImageMagick is able to detect hardware changes, driver updates, and new kernel sources and re-run the setup and the calibration test. You can also force ImageMagick to re-run the process by removing the content from the cache directory.
44 |In addition to the environment variables mentioned above, ImageMagick provides a set of APIs that allow developers to gain more fine-grained control of the OpenCL acceleration. For example, use the InitializeOpenCL() function to initialize the OpenCL environment:
45 | 46 |clEnv=GetCurrentOpenCLEnv();
47 | if (InitializeOpenCL(clEnv,exception) == MagickFalse)
48 | {
49 | /* looks like OpenCL is not supported */
50 | }
51 |