Concatenating images with ImageMagick


It sounds counter-intuitive, but I do almost all my image processing for this blog using my almost two-decade old Swiss Army Knife shell script library. Every image is scaled at multiple resolutions to save non-Retina readers bandwidth, and is sent through the excellent pngcrush and jpegoptim tools to losslessly reduce their size.

On the weekend I learned that ImageMagick’s append option can also be used to place images side by side, either horizontally or vertically. Note the operator changes from a minus to a plus:

$ magick convert \*.png -append vertical.png
$ magick convert \*.png +append horizontal.png

My mnemonic is to imagine the - is a dividing line, with images above and below.

Some of you may now be reasonably asking why I haven’t given a photographic example. That’s a great question. GraphicsMagick also has a similarly-named option, though I haven’t tested.

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