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ImageMagick — image swiss army knife

ImageMagick is the de-facto CLI for single-image and small-batch image transforms — convert, resize, crop, composite, annotate, filter. Bundled here under installMediaTools=true together with ffmpeg, ExifTool, and libvips.

  • Install:
    • macOS — Homebrew (brew install imagemagick), v7 with the unified magick binary. Managed by dot_ansible/roles/media_tools/tasks/main.yml when installMediaTools=true.
    • Linux — apt (sudo apt install imagemagick). Ubuntu 24.04 still ships v6, which exposes the legacy per-tool commands (convert, identify, mogrify, composite, …) instead of the unified magick. Same role / same flag.
  • Verify: magick --version (v7) or convert --version (v6).
  • Status in this repo: opt-in via installMediaTools=true. No automation calls into ImageMagick yet — it's there for ad-hoc image work.

v6 vs v7 — which command?

ImageMagick 7 unifies all the legacy executables behind a single magick entrypoint:

# v7 (macOS Homebrew)
magick input.png -resize 1280x output.png

# v6 (Ubuntu 24.04 apt)
convert input.png -resize 1280x output.png

magick accepts magick convert ..., magick identify ..., etc., for backward compatibility. To write portable scripts, prefer magick and fall back to convert:

IM=$(command -v magick || command -v convert)
"$IM" input.png -resize 1280x output.png

The rest of this page uses magick; mentally substitute convert on Ubuntu 24.04.

Common transforms

# Inspect
magick identify input.png                    # one-line summary
magick identify -verbose input.png | head -40

# Resize (preserve aspect)
magick input.png -resize 1280x output.png    # max width 1280
magick input.png -resize 1280x720 output.png # fit inside 1280×720

# Crop
magick input.png -crop 800x600+100+50 output.png   # WIDTHxHEIGHT+X+Y

# Quality / format
magick input.jpg -quality 85 output.jpg
magick input.png -background white -alpha remove output.jpg   # PNG → JPG, fill alpha

-resize 1280x keeps aspect; -resize 1280x720! (with !) forces exact dimensions and may distort.

Batch resize / convert

mkdir -p resized
for f in *.jpg; do
  magick "$f" -resize 1280x "resized/$f"
done

For thousands of files, see libvips — vipsthumbnail is 5–10× faster and uses a fraction of the memory.

mogrify (v6) / magick mogrify (v7) edits in place — fast but destructive:

magick mogrify -resize 1280x -path resized/ *.jpg     # writes to resized/, leaves originals alone
magick mogrify -resize 1280x *.jpg                    # OVERWRITES the originals

Compositing

# Overlay logo bottom-right with 20px margin
magick input.png logo.png \
  -gravity southeast -geometry +20+20 \
  -composite output.png

# Add solid border
magick input.png -bordercolor white -border 20 output.png

# Round corners (alpha mask trick)
magick input.png \
  \( +clone -alpha extract \
     -draw 'fill black polygon 0,0 0,15 15,0 fill white circle 15,15 15,0' \
     \( +clone -flip \) -compose Multiply -composite \
     \( +clone -flop \) -compose Multiply -composite \
  \) -alpha off -compose CopyOpacity -composite rounded.png

Compositing is where ImageMagick beats ffmpeg — the syntax is dense but designed for one-off image work.

Annotate

# Caption under an image
magick input.png \
  -gravity south -background "#00000088" -fill white \
  -splice 0x40 -annotate +0+10 'Caption text' \
  output.png

For repeatable styling, save a config file or wrap in a shell function.

Format conversion shortcuts

magick input.heic output.jpg     # HEIC → JPG (needs libheif support; check `magick -list format`)
magick input.svg -density 300 output.png   # SVG → high-DPI PNG
magick *.jpg output.pdf          # JPGs → multi-page PDF
magick input.pdf[0] cover.png    # First page of PDF → PNG (needs ghostscript)

PDF support depends on Ghostscript being installed. macOS Homebrew pulls it as a dep; on Ubuntu install separately (sudo apt install ghostscript).

Watch out

  • PDF / PostScript policy — recent Debian / Ubuntu builds ship with /etc/ImageMagick-6/policy.xml blocking PDF reads (CVE-2018-16509). If magick input.pdf cover.png errors with "not authorized", edit the policy or convert via pdftoppm first.
  • Memory limits — same policy.xml caps memory / area / disk. For big batches, prefer libvips.
  • Determinism — pin font, density, colorspace via flags so two runs produce byte-identical output. Useful for diffable visual tests.

See also