Image Processing

Image Processing Skill

Process images using ImageMagick command-line tools for conversion, optimization, and manipulation tasks.

Installation

macOS

brew install imagemagick

Ubuntu/Debian

sudo apt-get install imagemagick

Windows

winget install ImageMagick.ImageMagick
# Or download: https://imagemagick.org/script/download.php

Verify Installation

magick -version
# or
convert -version

Quick Start Examples

Image Processing

# Convert format
magick input.png output.jpg

# Resize maintaining aspect ratio
magick input.jpg -resize 800x600 output.jpg

# Create square thumbnail
magick input.jpg -resize 200x200^ -gravity center -extent 200x200 thumb.jpg

Batch Image Resize

# Resize all JPEGs to 800px width
mogrify -resize 800x -quality 85 *.jpg

# Output to separate directory
mogrify -path ./output -resize 800x600 *.jpg

Image Watermark

# Add watermark to corner
magick input.jpg watermark.png -gravity southeast \
  -geometry +10+10 -composite output.jpg

Common Workflows

Create Responsive Images

# Generate multiple sizes
for size in 320 640 1024 1920; do
  magick input.jpg -resize ${size}x -quality 85 "output-${size}w.jpg"
done

Batch Image Optimization

# Convert PNG to optimized JPEG
mogrify -path ./optimized -format jpg -quality 85 -strip *.png

Image Blur Effect

# Gaussian blur
magick input.jpg -gaussian-blur 0x8 output.jpg

Advanced Techniques

Complex Image Pipeline

# Resize, crop, border, adjust
magick input.jpg \
  -resize 1000x1000^ \
  -gravity center \
  -crop 1000x1000+0+0 +repage \
  -bordercolor black -border 5x5 \
  -brightness-contrast 5x10 \
  -quality 90 \
  output.jpg

Animated GIF from Images

# Create with delay
magick -delay 100 -loop 0 frame*.png animated.gif

# Optimize size
magick animated.gif -fuzz 5% -layers Optimize optimized.gif

Media Analysis

Image Information

# Basic info
identify image.jpg

# Detailed format
identify -verbose image.jpg

# Custom format
identify -format "%f: %wx%h %b\n" image.jpg

Performance Tips

1. Batch with mogrify - In-place image processing
2. Strip metadata - Reduce file size with -strip
3. Progressive JPEG - Better web loading with -interlace Plane
4. Limit memory - Prevent crashes on large batches
5. Test on samples - Verify settings before batch
6. Parallel processing - Use GNU Parallel for multiple files

Reference Documentation

Detailed guides in references/:

• imagemagick-editing.md - Format conversion, effects, transformations
• imagemagick-batch.md - Batch processing, mogrify, parallel operations

Common Parameters

ImageMagick Geometry

• 800x600 - Fit within (maintains aspect)
• 800x600! - Force exact size
• 800x600^ - Fill (may crop)
• 800x - Width only
• x600 - Height only
• 50% - Scale percentage

Troubleshooting

ImageMagick "not authorized"

# Edit policy file
sudo nano /etc/ImageMagick-7/policy.xml
# Change <policy domain="coder" rights="none" pattern="PDF" />
# to <policy domain="coder" rights="read|write" pattern="PDF" />

Memory errors

# Limit memory usage
magick -limit memory 2GB -limit map 4GB input.jpg output.jpg

Resources

• ImageMagick: https://imagemagick.org/
• ImageMagick Usage: https://imagemagick.org/Usage/