CLI Imagemagick

ImageMagick — Image Manipulation Suite

Repo: https://github.com/ImageMagick/ImageMagick

Create, edit, compose, and convert images from the command line. Supports 200+ formats. The standard tool for programmatic image manipulation.

Note: ImageMagick 7+ uses the magick command. Version 6 uses convert, identify, mogrify, etc. as separate commands. Examples use magick (v7) — replace with convert/identify/mogrify if on v6.

When to Activate

Manual triggers:

• "Resize these images"
• "Convert images to PNG/JPEG/WebP"
• "Create a thumbnail"
• "Watermark images"
• "Create a favicon"
• "Make an animated GIF from frames"

Auto-detect triggers:

• User needs to batch-process a folder of images
• User needs image assets at specific dimensions for web/app
• User wants to add text or a logo overlay to images
• User extracted frames from FFmpeg and wants to process them

Key Commands

Inspect Images (magick identify)

magick identify image.png                        # Basic info (format, size, depth)
magick identify -verbose image.png              # Full metadata
magick identify -format "%wx%h\n" *.jpg         # Print dimensions for all JPEGs
magick identify -format "%f: %wx%h %[colorspace]\n" *.png  # Custom format

Basic Conversion

magick input.png output.jpg                     # Convert format
magick input.jpg -quality 85 output.jpg         # Set JPEG quality (1-100)
magick input.png -quality 90 output.webp        # Convert to WebP
magick *.png output.pdf                         # Combine images into PDF
magick input.pdf output-%04d.png               # PDF pages to PNG sequence

Resize (-resize)

magick input.jpg -resize 800x600 output.jpg     # Resize to fit within 800x600
magick input.jpg -resize 800x output.jpg        # Width 800, height proportional
magick input.jpg -resize x600 output.jpg        # Height 600, width proportional
magick input.jpg -resize 800x600! output.jpg    # Force exact size (distorts)
magick input.jpg -resize 800x600^ output.jpg    # Fill (crop to fit) 800x600
magick input.jpg -resize 50% output.jpg         # 50% of original size
magick input.jpg -resize 800x600> output.jpg    # Only shrink (don't enlarge)
magick input.jpg -resize 800x600< output.jpg    # Only enlarge (don't shrink)

Crop (-crop)

magick input.jpg -crop 400x300+100+50 output.jpg  # width x height + x_offset + y_offset
magick input.jpg -gravity Center -crop 400x300+0+0 output.jpg  # Crop from center
magick input.jpg -trim output.jpg                  # Auto-trim whitespace/border

Rotate, Flip, Flop

magick input.jpg -rotate 90 output.jpg          # Rotate 90° clockwise
magick input.jpg -rotate -45 output.jpg         # Rotate 45° counter-clockwise
magick input.jpg -flip output.jpg               # Vertical flip
magick input.jpg -flop output.jpg               # Horizontal flip
magick input.jpg -auto-orient output.jpg        # Fix EXIF orientation

Color Adjustments

magick input.jpg -brightness-contrast 10x20 output.jpg     # Brightness +10, contrast +20
magick input.jpg -modulate 100,150,100 output.jpg           # Brightness,Saturation,Hue
magick input.jpg -colorspace Gray output.jpg                # Grayscale
magick input.jpg -negate output.jpg                         # Invert colors
magick input.jpg -level 20%,80% output.jpg                 # Levels (black/white point)
magick input.jpg -sigmoidal-contrast 3,50% output.jpg      # S-curve contrast
magick input.jpg -colorize 10,0,0 output.jpg               # Add red tint

Blur and Sharpen

magick input.jpg -blur 0x2 output.jpg           # Gaussian blur, radius 0, sigma 2
magick input.jpg -sharpen 0x1 output.jpg        # Unsharp mask sharpen
magick input.jpg -unsharp 0x1+0.5+0.1 output.jpg  # Fine-tuned unsharp mask
magick input.jpg -median 3 output.jpg           # Median filter (noise reduction)

Text Overlay (-annotate)

magick input.jpg \
  -font Arial -pointsize 48 -fill white -gravity South \
  -annotate +0+20 "Photo Caption" \
  output.jpg

# With stroke/outline
magick input.jpg \
  -font Arial -pointsize 48 \
  -fill white -stroke black -strokewidth 2 \
  -gravity Center -annotate +0+0 "Watermark" \
  output.jpg

Border and Padding

magick input.jpg -border 10x10 -bordercolor white output.jpg  # White border
magick input.jpg -border 5% -bordercolor black output.jpg      # 5% border
magick input.jpg -gravity Center -extent 900x600 output.jpg    # Pad to exact canvas size

Shadow and Effects

magick input.png -background none -shadow 50x5+4+4 \
  \( +clone -background none -shadow 50x5+4+4 \) \
  +swap -background white -layers merge output.png

magick input.jpg -vignette 0x20 output.jpg      # Vignette effect
magick input.jpg -charcoal 1 output.jpg         # Charcoal sketch effect
magick input.jpg -oil-paint 3 output.jpg        # Oil paint effect

Transparency (-alpha)

magick input.png -alpha set -background none output.png         # Preserve transparency
magick input.jpg -transparent white output.png                  # Make white pixels transparent
magick input.png -fuzz 10% -transparent "#ffffff" output.png   # Fuzzy transparency

Advanced Patterns

Batch Processing with mogrify (in-place)

# Resize all JPEGs in a folder (modifies originals!)
magick mogrify -resize 1200x1200> *.jpg

# Convert all PNGs to JPEG (different extension = new files)
magick mogrify -format jpg *.png

# Resize and add watermark to all images, output to ./thumbs/
mkdir -p thumbs
magick mogrify -path thumbs -resize 300x300^ -gravity Center \
  -extent 300x300 -font Arial -pointsize 18 -fill "rgba(255,255,255,0.5)" \
  -gravity SouthEast -annotate +5+5 "© 2024" *.jpg

Create Favicon (Multi-Size ICO)

# Generate all sizes from a source SVG or large PNG
magick source.png -resize 16x16 favicon-16.png
magick source.png -resize 32x32 favicon-32.png
magick source.png -resize 48x48 favicon-48.png
magick source.png -resize 64x64 favicon-64.png

# Combine into .ico
magick favicon-16.png favicon-32.png favicon-48.png favicon-64.png favicon.ico

# One-liner
magick source.png -define icon:auto-resize=64,48,32,16 favicon.ico

Thumbnail Generation with Cropping

# Smart crop (crop-to-fill at exact size)
magick input.jpg -resize 300x300^ -gravity Center \
  -crop 300x300+0+0 +repage thumb.jpg

# Batch thumbnails preserving aspect ratio (letterbox)
magick input.jpg -thumbnail 300x300 -background white \
  -gravity Center -extent 300x300 thumb.jpg

Watermarking

# Image watermark (logo overlay)
magick composite -gravity SouthEast -geometry +10+10 \
  logo.png input.jpg output.jpg

# Semi-transparent text watermark across entire image
magick input.jpg \
  \( -size 200x50 xc:none -font Arial -pointsize 24 \
     -fill "rgba(255,255,255,0.3)" -gravity Center \
     -annotate 0 "CONFIDENTIAL" \) \
  -gravity Center -composite output.jpg

Image Comparison

magick compare input1.jpg input2.jpg diff.jpg         # Visual diff
magick compare -metric PSNR input1.jpg input2.jpg diff.jpg  # PSNR metric
magick compare -metric AE input1.jpg input2.jpg diff.jpg    # Absolute error pixels

Create Animated GIF from Frames

# From image sequence (50ms delay = 20fps)
magick -delay 5 -loop 0 frame*.png animation.gif

# Control per-frame delay
magick \( frame1.png -delay 100 \) \( frame2.png -delay 50 \) \
  -loop 0 animation.gif

# Optimize GIF file size
magick -delay 5 -loop 0 frame*.png -layers optimize animation.gif

Create Contact Sheet / Montage

# 4-column contact sheet with labels
magick montage *.jpg -geometry 200x200+5+5 -tile 4x montage.jpg

# Uniform grid, white background
magick montage *.png -background white -geometry 150x150+2+2 \
  -tile 5x -border 1 -bordercolor gray sheet.jpg

Color Profile Conversion

magick input.jpg -profile /path/to/sRGB.icc -profile /path/to/CMYK.icc output.tif
magick input.jpg -colorspace sRGB output.jpg                # Convert to sRGB
magick input.jpg -strip output.jpg                          # Strip all metadata/profiles

SVG to PNG Rendering

magick -background none input.svg output.png               # Transparent background
magick -background white -density 150 input.svg output.png # 150 DPI rasterization
magick -density 300 input.svg -resize 1000x output.png    # High-res render

PDF to Images

# Requires Ghostscript
magick -density 150 input.pdf output-%04d.png    # All pages to PNG at 150 DPI
magick -density 150 "input.pdf[0]" cover.jpg    # First page only

Sprites for Web

# Horizontal sprite strip
magick icon1.png icon2.png icon3.png +append sprite.png

# Vertical sprite strip
magick icon1.png icon2.png icon3.png -append sprite.png

# Grid sprite
magick montage icon*.png -geometry +0+0 -tile 4x sprite.png

Chaining with Other Skills

• cli-ffmpeg: Extract video frames with FFmpeg (-vf fps=1 frame_%04d.png), then use ImageMagick's mogrify to batch-resize, watermark, or convert the frames
• fd: Use fd -e jpg to find all images recursively, pipe into a shell loop with magick for batch processing
• cli-fzf (fzf): Use fd -e png | fzf to interactively select an image before running a magick command
• cli-pandoc: Use ImageMagick to generate or preprocess images that are embedded in documents converted by Pandoc