Image optimization

Make a smaller copy of a JPEG, PNG, or WebP with ImageMagick. The original file stays where it is.

When to use

An image is larger than the place it is going: a page, an attachment, or a thumbnail. Resize it, drop the metadata, and write a new file. Compare the two before you replace anything.

Install

ImageMagick 7 installs the magick command. ImageMagick 6 installs convert. Use whichever one exists.

magick -version || convert -version

# Debian / Ubuntu
sudo apt-get install imagemagick

# macOS
brew install imagemagick

Pick the binary once and reuse it:

if command -v magick >/dev/null; then IM=magick; else IM=convert; fi

Commands

Shrink a photo so the longest side is at most 1600 pixels, bake in the orientation, strip metadata, and write a JPEG. The > suffix means "only shrink". Quote it so the shell does not treat it as a redirect.

"$IM" input.jpg -auto-orient -resize '1600x1600>' -quality 82 -strip output.jpg

PNG, still a new file. -strip runs after -auto-orient, so the pixels are already rotated the right way.

"$IM" input.png -auto-orient -resize '1600x1600>' -strip output.png

WebP from the same source:

"$IM" input.png -auto-orient -resize '1600x1600>' -quality 80 -strip output.webp

Look at dimensions and byte sizes before you keep the result.

identify input.jpg output.jpg
ls -l input.jpg output.jpg

Gotchas

• mogrify writes over the file you name. These examples use magick or convert so the original stays put.
• -strip removes profiles, comments, and EXIF, including GPS. Run -auto-orient first, or a phone photo can come out sideways.
• An unquoted 1600x1600> is a shell redirect. Keep the quotes.
• Quality 82 is a reasonable JPEG. Lower numbers get smaller and softer. Look at the output before you go further down.
• A file that is already small can grow when you change format. Keep the original when ls shows the new file is larger.

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