ImageMagick is a set of CLI tools and a C library for performing a variety of digital image handling tasks, such as converting between formats, resizing, mirroring, rotating, adjusting colors, rendering text, drawing shapes and so on. In many cases ImageMagick is not being used directly, but exists as part of the hidden substrate of C code that the modern shiny stuff is built upon. For example, it may be used to generate thumbnails of images that users uploaded to a web application. ImageMagick supports more than 200 image formats and runs on all the major operating systems. If you’re running Linux, macOS or other well established Unix system it will most likely be available through your package manager.
ImageMagick can be used through the following CLI tools:
animate- animate a sequence of images (requires X Windows).conjure- run an image processing script written in XML-based Magick Scripting Language (MSL).display- show a single image (requires X Windows).magick- general purpose CLI tool for pretty much everything. This one is recommended for modern usage. Others are leftovers from legacy versions of ImageMagick.convert- convert between image formats, optionally with some tranformations.composite- overlap or overlay two or more image on each other.montage- combine several images into a single output image.compare- show difference between images.identify- describes one or more image files and prints their metadata.import- save a screenshot of entire X Windows screen or some portion of it.stream- extract raw values of pixel components.
Let us start simple by extracting some metadata from image files. For the sake of example, we will use a geotagged image file that contains GPS coordinates within EXIF fields.
$ wget https://www.geoimgr.com/images/samples/irland-dingle.jpg
--2022-08-13 13:10:14-- https://www.geoimgr.com/images/samples/irland-dingle.jpg
Resolving www.geoimgr.com (www.geoimgr.com)... 108.157.214.28, 108.157.214.104, 108.157.214.75, ...
Connecting to www.geoimgr.com (www.geoimgr.com)|108.157.214.28|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 694078 (678K) [image/jpeg]
Saving to: ‘irland-dingle.jpg’
irland-dingle.jpg 100%[================================================================================================================>] 677,81K 979KB/s in 0,7s
2022-08-13 13:10:16 (979 KB/s) - ‘irland-dingle.jpg’ saved [694078/694078]
$ file irland-dingle.jpg
irland-dingle.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, Exif Standard: [TIFF image data, little-endian, direntries=14, manufacturer=Panasonic, model=DMC-FX60, orientation=upper-left, xresolution=202, yresolution=210, resolutionunit=2, software=Ver.1.0 , datetime=2012:09:16 16:58:02, GPS-DataTIFF image data, little-endian, direntries=14, manufacturer=Panasonic, model=DMC-FX60, orientation=upper-left, xresolution=202, yresolution=210, resolutionunit=2, software=Ver.1.0 , datetime=2012:09:16 16:58:02, GPS-Data], baseline, precision 8, 2048x1536, components 3
$ magick identify -verbose irland-dingle.jpg
Image:
Filename: irland-dingle.jpg
Format: JPEG (Joint Photographic Experts Group JFIF format)
Mime type: image/jpeg
Class: DirectClass
Geometry: 2048x1536+0+0
Resolution: 92.16x92.16
Print size: 22.2222x16.6667
Units: PixelsPerInch
Colorspace: sRGB
Type: TrueColor
Base type: Undefined
Endianness: Undefined
Depth: 8-bit
Channel depth:
Red: 8-bit
Green: 8-bit
Blue: 8-bit
Channel statistics:
Pixels: 3145728
Red:
min: 0 (0)
max: 255 (1)
mean: 147.255 (0.57747)
median: 139 (0.545098)
standard deviation: 71.5477 (0.280579)
kurtosis: -1.25311
skewness: 0.0244421
entropy: 0.960027
Green:
min: 0 (0)
max: 255 (1)
mean: 146.551 (0.574708)
median: 137 (0.537255)
standard deviation: 73.5709 (0.288513)
kurtosis: -1.26019
skewness: 0.0407684
entropy: 0.957017
Blue:
min: 0 (0)
max: 255 (1)
mean: 148.024 (0.580487)
median: 140 (0.54902)
standard deviation: 73.7421 (0.289185)
kurtosis: -1.28316
skewness: 0.0582366
entropy: 0.937305
Image statistics:
Overall:
min: 0 (0)
max: 255 (1)
mean: 147.277 (0.577555)
median: 138.667 (0.543791)
standard deviation: 72.9536 (0.286092)
kurtosis: -1.26427
skewness: 0.0417203
entropy: 0.951449
Rendering intent: Perceptual
Gamma: 0.454545
Chromaticity:
red primary: (0.64,0.33)
green primary: (0.3,0.6)
blue primary: (0.15,0.06)
white point: (0.3127,0.329)
Matte color: grey74
Background color: white
Border color: srgb(223,223,223)
Transparent color: none
Interlace: None
Intensity: Undefined
Compose: Over
Page geometry: 2048x1536+0+0
Dispose: Undefined
Iterations: 0
Compression: JPEG
Quality: 90
Orientation: TopLeft
Profiles:
Profile-exif: 16766 bytes
Properties:
date:create: 2022-08-13T10:10:16+00:00
date:modify: 2019-07-13T17:45:39+00:00
date:timestamp: 2022-08-13T10:13:31+00:00
exif:ColorSpace: 1
exif:ComponentsConfiguration: ....
exif:CompressedBitsPerPixel: 4/1
exif:Contrast: 0
exif:CustomRendered: 0
exif:DateTime: 2012:09:16 16:58:02
exif:DateTimeDigitized: 2012:09:16 16:58:02
exif:DateTimeOriginal: 2012:09:16 16:58:02
exif:DigitalZoomRatio: 0/10
exif:ExifOffset: 648
exif:ExifVersion: 0221
exif:ExposureBiasValue: 0/100
exif:ExposureMode: 0
exif:ExposureProgram: 2
exif:ExposureTime: 10/2000
exif:FileSource: .
exif:Flash: 24
exif:FlashPixVersion: 0100
exif:FNumber: 40/10
exif:FocalLength: 77/10
exif:FocalLengthIn35mmFilm: 43
exif:GainControl: 0
exif:GPSInfo: 10396
exif:GPSLatitude: 52/1, 8/1, 20155/942
exif:GPSLatitudeRef: N
exif:GPSLongitude: 10/1, 16/1, 17981/630
exif:GPSLongitudeRef: W
exif:GPSVersionID: ....
exif:InteroperabilityOffset: 10366
exif:LightSource: 0
exif:Make: Panasonic
exif:MakerNote: Panasonic...=......................................................... ...................................%... ...........!.... ..h..."...........#...........$...........%.......p'..&.......0291'...........(...........).......?...*...........+...........,...........-......................./...........0...........1...........2...........3........'..4...........5...........6.......??..7...........8...........:...........;...........<.......??..=...........>...........?...........M........'..N...*...?'..O...........W...........Y...........]...........^...........a.......?'..b...........c...................0132........%...................................?.......................................................................b(..............DV..EP..??DB?.??AF?.??..??..??.0??..ʯ2.??..??..??..??????..??..??..??X.???.ȯ@.د????..??..Ư..ίB.ү..Я(.??v.??>.??>.ԯ0.?? .?(.?..?..௯.??.??.??.?..??..گ..֯..?........?..?...?...?...?..??ST.. ?.."?..$?..&?..(?..*?..,?...?..0?..2?..4?..6?..8?..:?..<?..`?..b?..d?..h?..f?..j?..x?..|?..~?..>?..p?..r?..t?..v?..R?..L?..N?..P?..??AEn..?,..?X..?,..?...?...?..*?..,?..$??.>?..2? ..??.(?...?.. ?f."??.0?#.&?..??..????4?...???.???.?..??..?????..?...???¦??.?...?..??...?...???.?...???.?..T?..V?..D??.J??.F??.H?..N?..^?..R?..X?..@?..B??.`?..Z?..\?...??.d?...?..b?...?..L?..??..??..??..6?..j?..l?..n?6.Ħ..Ʀ..Ȧ].ʦ9.̦..Φa.Ц..֦..ئ..Ҧ..Ԧ..??#.??..??#.??..0?x..?x..?P..?W..?#[email protected]?..??WB2..??..?...?...?...?..h?..`?o.d??.f?..@??.B?..D?..F? .??j.???.??..??..??u.??".??s.??..???.??..??..???.??j.???.??..??..j?..l?!..??..?..b??.??d.Ȩ..¨?.ʨ?.Ĩ??̨..ƨ..Ψ..Ш..$?..&?.. ?.."?..(??.*?..,?...?..0?..2?..H??.J?..L??.N?..P??.R?..T??.V?...?\..?j..?...?...?...?...?...?...?...?...?...?...?...?..??YC?.N?..P?..R?..T?..D?..F???H?..J?..L?..8?..:?..<?..>?...?..0??.2?fD4?".6?...............?`.`?..b?..d?Xrf?Xrh?]]j?..l?..n?...?...?...?...?...?...?...?...?...?...?..???.??..???.??..??..X?..Z?..\?..^? ..?...?..????ª??Ī??ƪ??Ȫ????CM..?. p.?..??..ک..ܩ..??DS:..?...?...??..??..?...?...??U.?uU.?"".?! .?"".?! .?..??ISn..?..??..??..???.??...?...?e..?...?e..?...?...??..?<..?n..?N..?...??..??..??..??..??..??..??..??..??..??.??FD?.`?..b?...?...?...?...?...?...?...?...?...?...?...?...?...?...?...?...?..@?..B?..D?..F?..H?..J?..L?..N?..P?..R?..T?..V?..X?..Z?..\?..^?..ħ..̧..Χ..Ч..ʧd.§..??ATB.<?.."?..$?..&?..(?..*?..,?...?..0?..2?..4?..6?..8?..:?..>?..??IAn.???.???.??..??..??????????????????..??..??..??..????????????????.?r..?...?...?...?...?...?!..?...?...?..........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................MOIS..?...,...?...8.,.p.L.x.?.....?... .?... .?...?.?.`.?.?.....@.(.T.,.?.<.?.(...h.?...p...h.D.....?.$...d.8.?.x. ...?.T.?.?.........?.....L...X.?.?. 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exif:MaxApertureValue: 30/10
exif:MeteringMode: 5
exif:Model: DMC-FX60
exif:PhotographicSensitivity: 80
exif:PixelXDimension: 2048
exif:PixelYDimension: 1536
exif:PrintImageMatching: PrintIM.0250..................d.............................?.................?..........................'.......'.......'..?....'.......'..^....'.......'..?....'..?....'......................................
exif:Saturation: 0
exif:SceneCaptureType: 0
exif:SceneType: .
exif:SensingMethod: 2
exif:Sharpness: 0
exif:Software: Ver.1.0
exif:thumbnail:Compression: 6
exif:thumbnail:InteroperabilityIndex: R98
exif:thumbnail:InteroperabilityVersion: 0100
exif:thumbnail:JPEGInterchangeFormat: 10628
exif:thumbnail:JPEGInterchangeFormatLength: 6131
exif:thumbnail:Orientation: 1
exif:thumbnail:ResolutionUnit: 2
exif:thumbnail:XResolution: 180/1
exif:thumbnail:YCbCrPositioning: 2
exif:thumbnail:YResolution: 180/1
exif:WhiteBalance: 0
exif:YCbCrPositioning: 2
jpeg:colorspace: 2
jpeg:sampling-factor: 2x2,1x1,1x1
signature: 43f09d8ff5c5df045697fccde02cd88200c8c657eb4c2458a48c72a4cd8a9576
unknown: ................................................................
Artifacts:
verbose: true
Tainted: False
Filesize: 694078B
Number pixels: 3.14573M
Pixel cache type: Memory
Pixels per second: 74.1853MP
User time: 0.030u
Elapsed time: 0:01.042
Version: ImageMagick 7.1.0-45 Q16-HDRI aarch64 20319 https://imagemagick.org
We see that ImageMagick was able to print far more information on the image file than a standard Unix file(1) utility. Not only it printed some image representation characteristics, but it also gave us the entire EXIF metadata including coordinates, camera settings and information on technical properties of the camera. All of this leaks quite a bit of information on how, where and when the picture was taken and can be valuable to those working on digital forensics. Furthemore, it computed various statistical properties of pixel component value distribution within the image (e.g. mean, median, standard deviation, entropy).
Let us try doing some transformations on the image. Converting the image file to another format is rather simple:
$ magick convert irland-dingle.jpg irland-dingle.png
$ magick identify irland-dingle.png
irland-dingle.png PNG 2048x1536 2048x1536+0+0 8-bit sRGB 3.22077MiB 0.000u 0:00.000
What if we wanted to make it grayscale? The convert (sub-)command can also be used for this:
$ convert -colorspace Gray irland-dingle.png irland-dingle-gray.png
$ magick identify irland-dingle-gray.png
irland-dingle-gray.png PNG 2048x1536 2048x1536+0+0 8-bit Gray 256c 1.36152MiB 0.000u 0:00.001
That’s one way to do this. For another ways, see:
- Convert RGB to Grayscale in ImageMagick command-line on StackOverflow
Resizing the image is also fairly simple:
$ magick convert irland-dingle.png -resize 64x64 irland-dingle-thumb.png
$ magick identify irland-dingle-thumb.png
irland-dingle-thumb.png PNG 64x48 64x48+0+0 8-bit sRGB 28196B 0.000u 0:00.000
Note that by default this will keep the original aspect ratio of the image, thus the result image
may not be of size you passed into -resize argument or may have some empty parts. To force the
resizing into an exact size we provide, we need to use exclamation marks next to width and height values:
$ magick convert irland-dingle.png -resize 64\!x64\! irland-dingle-thumb-forced.png
For further information on resizing, see the official documentation.
However there is more to image processing than simple stuff like this. Digital image processing is a fairly large field that deals with computational handling of image data for applications such as image compression, computational photography, medical imaging, augmented reality, computer vision and others.
One of the foundational techniques of digital image processing is convolutions that entails applying a linear-algebra based filter on images. Convolution kernel is a two dimensional table of numbers (matrix) that defines how the output image is created from input image. For example, low pass filter that implements a simple image blurring can be implemented by a square matrix with each member being a constant:
$ magick convert irland-dingle.png -convolve "3x3: 0.1111, 0.1111, 0.1111 0.1111, 0.1111, 0.1111 0.1111, 0.1111, 0.1111" irland-dingle-blur.png
In fact, ImageMagick has some pre-made kernels for Gaussian blurring, among other applications:
$ magick convert irland-dingle.png -convolve Gaussian:0x8 irland-dingle-blur-gaussian.png
Since ImageMagick is a bunch of CLI tools it can already be used as part of automation scripts by calling magick(1) program as subprocess or by writing a shell script that launches it with the appropriate arguments. However, ImageMagick also exposes two kinds of C APIs. MagickWand is high-level, thread safe API and MagickCore is a low-level one. Most developers should only consider using MagickWand. Don’t worry if you don’t want to deal with C programming language. Wrappers in multiple popular programming languages are available:
- Magick++ for C++.
- Go Imagick for Go.
- JMagick for Java.
- Wand for Python.
- MagickRust for Rust.
For a real-world code that uses ImageMagick, see textcleaner script for cleaning up images of text before applying OCR on them. Potentially something like this can be implemented to deal with simple image captchas that can be decoded with something like Tesseract when proper pre-processing has been applied.