ImageMagick Command‑Line Guide: Installation, Basic Commands, Formats and Practical Examples

ImageMagick is a powerful command‑line suite for creating, editing, converting and compositing images, supporting over 200 formats including PNG, JPEG, GIF, PDF and SVG.

Installation – on macOS you can install it with brew install imagemagick . The official download page also provides binaries for Linux, Windows and other platforms.

Basic commands – after installation the following sub‑commands are available:

magick : general image creation, editing and conversion.

convert : alias of magick for backward compatibility.

identify : prints image format, resolution, size, colorspace, etc.

mogrify : like magick but overwrites the original file.

composite : combines one or more images into a new image.

montage : creates a composite image from multiple independent images.

compare : compares two images mathematically and visually.

display , animate , import , conjure , stream and others for various advanced tasks.

Command format follows the Unix style: command [options] input_image output_image . For multiple inputs you can use command [options] image1 [options] image2 output_image .

Resize example – to create a 150×100 thumbnail from goods.jpg :

convert -resize 150x100 -quality 70 -strip goods.jpg thumbnail.jpg

The -resize flag also accepts modifiers:

! – force exact dimensions.

> – resize only if the image is larger than the given size.

< – resize only if the image is smaller.

Watermark example – add a centered transparent text watermark:

convert -draw 'text 0,0 "JD.COM"' -fill 'rgba(221,34,17,0.25)' -pointsize 36 -font 'cochin.ttc' -gravity center joy.jpg watermark.jpg

For tiled, rotated watermarks you can first create a transparent canvas with -size and xc:none , draw the text, then pipe it to composite using -tile and -dissolve .

Captcha generation – a fixed‑value example that draws four characters with different colors, rotations and bezier noise:

convert 'xc:[100x40!]' -pointsize 20 -font 'cochin.ttc' \
  -gravity NorthWest -strokewidth 1 -fill '#b72b36' -stroke '#b72b36' \
  -draw 'translate 13,19 rotate 10 text -5,-8 "5"' \
  -fill '#821d70' -stroke '#821d70' -draw 'translate 36,13 rotate -8 text -8,-8 "C"' \
  -fill '#c7960a' -stroke '#c7960a' -draw 'translate 60,23 rotate 5 text -5,-8 "2"' \
  -fill '#03610a' -stroke '#03610a' -draw 'translate 85,25 rotate 13 text -8,-8 "E"' \
  -strokewidth 2 -stroke 'rgba(248,100,30,0.5)' -fill 'rgba(0,0,0,0)' \
  -draw 'bezier -20,30 -16,10 20,2 50,20' -draw 'bezier 50,20 78,42 138,36 140,16' +noise Impulse captcha.jpg

Clone and append – using image stacks to crop, resize, flip and combine images:

convert \ 
  ( -crop 300x300+10+25 joy.jpg ) \ 
  ( -resize 400x400 -crop 300x300+50+0 logo: ) -swap 0,1 +append \ 
  ( -clone 0 -flop -flip ) -append -resize 200x200 combined.jpg

GIF ↔ image conversion – extract frames:

convert -coalesce rain.gif frame_%d.jpg

Or extract a specific frame:

convert -coalesce 'rain.gif[0]' first_frame.jpg

To re‑assemble frames into an animated GIF with infinite looping:

convert -loop 0 frame-*.jpg rain_animation.gif

Use leading zeros ( frame-001.jpg ) to keep correct order.

PDF ↔ image conversion – requires Ghostscript ( brew install ghostscript ). Two approaches:

convert -density 150 -flatten 'download.pdf[0]' first_page.jpg

or

convert -density 150 -background white -alpha remove download.pdf download.jpg

The -density option sets DPI for clearer output.

Node.js integration – execute ImageMagick commands via child_process :

const util = require('util');
const exec = util.promisify(require('child_process').exec);
await exec(`convert -resize '150x100!' -strip goods.jpg thumbnail.jpg`);

For streaming data use spawn :

const cp = require('child_process');
const fs = require('fs');
const args = ['-', '-resize', '150x100!', '-strip', 'jpg:-'];
const proc = cp.spawn('convert', args);
fs.createReadStream('/path/to/goods.jpg').pipe(proc.stdin);
proc.stdout.pipe(response);

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