Make, modify and convert images with ImageMagick
ImageMagick is a powerful free software suite of command line tools for manipulating images. For this reason, it's often called the "swiss army knife" of image tools.
Resources
ImageMagick tools
ImageMagick provides a number of command line tools, none of which are named ImageMagick, but instead:
- convert, which creates/modifies an image and saves it as a new file
- mogrify, which makes changes to an image "in-place"
- montage, which creates a "thumbnail" image of a number of images in a grid
- identify, which displays information about an image
- display, which shows an image in a window
ImageMagick often comes with operating systems, such as Linux distributions. Type the name of one of the above commands in a terminal/shell, such as:
convert
If ImageMagick is installed on your machine, you should see an extensive manual of options for the convert tool.
Installing ImageMagick
In Linux, ImageMagick should either already be installed, or is available via whatever package manager the distribution supports. In Debian/Ubuntu:
sudo apt-get install imagemagick
or on Mac OS, try:
brew install imagemagick
A (basic) guide to ImageMagick tools and their options
Checking the version of ImageMagick you have
Use the --version option with an ImageMagick command.
convert --version
You should see something like this:
Version: ImageMagick 7.1.0-5 Q16 arm 2021-08-22 https://imagemagick.org
Creating new images (without changing any originals)
Use convert. This command always produces a new output file, named it is given at the end of the command.
convert original.png -resize 160x120 icon.png
Modifying images "in-place" (changing the originals)
Resizing a folder of images with mogrify
WARNING: This command replaces all the images in the current folder with thumbnails, writing over the files that are there. If you want to keep the originals, make a copy first!
mogrify -resize 320x240 *
Mogrify supports the same options as convert, only it modifies its input, replacing the original (so you need to be careful with it).
It can be used with a wildcard to modify many files at once.
mogrify -resize 320x240 *.JPG
Getting information about an image
identify original.png
Displaying an image
display foo.png
Cutting
Cutting out a particular-shaped rectangle from an image
The format of the crop option is: WIDTHxHEIGHT+LEFT+TOP
For instance, to extract a 256 pixel square from an image 500 pixels from the left, at the top (0):
convert FILE0058.JPG -crop 256x256+500+0 tile.jpg
Cutting an image up into tiles or strips, aka "Cookie Cutting"
The crop command, when not given a specific position to cut out, will repeat as many times as it can, "cookie-cutter style", producing a series of images.
convert original.png -crop 64x64 tile%04d.png
convert original.png -crop 64x strip%04d.png
convert original.png -crop x64 bar%04d.png
Transforming
Converting/Changing image formats
convert original.png new.jpg
convert original.png -quality 1 lo.jpg
Resizing images
convert -resize 640x640 FILE0058.JPG work.png
convert -resize 640x640! FILE0058.JPG work.png
Assembling
Creating an animated gif from multiple images
convert tile*.png slide.gif
convert -delay 5 -dispose background -page +0+0 tile*.png slide.gif
Overlaying/Combining 2 images into a new image
Use composite. Composite is both a command-line tool on its own, and also it's available via the "-composite" option of convert. Note that the order of things is different depending on which way you use it.
Creating a "contact sheet" / table of images
This tool arranges images in a grid, based on the specifications given in the options and output filename.
Using montage, arrange the frames as tiles on new jpg files. The -geometry option describes how big each image is resized to (640) and the spacing in between the tiles (+10+10).
%04d in the output filename means that the results are numbered starting from 0001 (0-padded to 4 places).
montage -geometry '640x640>+10+10' -tile 1x3 /*.jpg test%04d.jpg
Drawing
Create shapes using convert.
convert -size 300x300 xc:lightgray -fill black -draw 'rectangle 0,0 150,150' rect.gif
convert -size 300x300 xc:lightgray -fill black -draw 'circle 150,150 50,40' circle.gif