Commmonly used imagemagick commands.
ImageMagick is an open source tool for editing and converting raster images created in 1987 by John Cristy.
I use ImageMagick on the command line for quick image edits such as cropping, resizing or rotating. It is also used in the batchVariants script that prepares the images for this website.
Use convert to create a new output file or mogrify to overwrite the input file.
Rotating
mogrify -rotate "90" file.jpg
Rotates an image by 90 degrees clockwise.
Cropping
convert -crop 640x480+50+100 +repage input.jpg output.jpg
Crops the image at X:50 Y:100 to a size of W: 640 H:480.+repage will prevent export of the cropped area.
convert -crop 3:2+50+100 +repage input.jpg output.jpg
Crops the image at X:50 Y:100 to a ratio of W: 3 H:2
convert -crop 3:2+50+100 +repage input.jpg output.jpg
Crops the image at X:50 Y:100 to a ratio of W: 3 H:2
Resizing
mogrify -geometry 50% file.jpg
Resizes the image down by half.
mogrify -geometry 1024x file.jpg
Resizes the image to a width of 1024px.
mogrify -geometry x800 file.jpg
Resizes the image to a height of 800px.
mogrify -geometry 800x800 file.jpg
Resizes the image to 800px at the longer side.
mogrify -density 72 -units pixelsperinch file.jpg
Changes the DPI of the image to 72.
Dithering
convert input.jpg -dither FloydSteinberg -colors 8 output.jpg
Dithers the image with 8 colors.
convert input.jpg -dither FloydSteinberg -remap colortable.gif output.jpg
Dithers the image using a colortable.
Tiling
montage * output.jpg
Tiles all images in folder.
montage * output.jpg -background "#000000"
Sets the background color the black.
PDF conversion
convert file.pdf -flatten output.jpg
Converts a pdf to.jpg
Image Sequencing
convert -delay 200 -loop 0 *.jpg output.gif
Creates an infinitely looping GIF with 2 seconds delay between each frame.
Information
identify file.jpg
Displays information on the file such as width and height.
Offline Documentation
To make the documentation available offline, install the imagemagick-6-doc package.