imagemagick-conversion

ImageMagick Image Conversion

Project: Project-independent Gitignored: Yes

Trigger

Use this skill when users request image manipulation tasks including:

• Converting between image formats (PNG, JPEG, WebP, GIF, TIFF, etc.)
• Resizing images (dimensions, percentages, aspect ratios)
• Batch processing multiple images
• Adjusting image quality and compression
• Creating thumbnails
• Basic image transformations (rotate, flip, crop)

Overview

ImageMagick is a powerful command-line tool for image processing. This skill provides guidance for using the magick command to perform common image conversion and manipulation tasks.

Key Command Pattern:

magick input-file [options] output-file

Common Use Cases

Format Conversion

Basic format conversion:

magick image.jpg image.png
magick photo.png photo.webp

Batch convert all JPEGs to PNG:

magick mogrify -format png *.jpg

Convert with specific output directory:

mkdir -p output
magick mogrify -format webp -path output/ *.jpg

Resizing Images

Resize by percentage:

magick image.jpg -resize 50% output.jpg

Resize to specific width (maintain aspect ratio):

magick image.jpg -resize 800x output.jpg

Resize to specific height (maintain aspect ratio):

magick image.jpg -resize x600 output.jpg

Resize to fit within dimensions (maintain aspect ratio):

magick image.jpg -resize 800x600 output.jpg

Resize to exact dimensions (ignore aspect ratio):

magick image.jpg -resize 800x600! output.jpg

Resize only if larger:

magick image.jpg -resize '800x600>' output.jpg

Resize only if smaller:

magick image.jpg -resize '800x600<' output.jpg

Quality and Compression

Set JPEG quality (1-100, default 92):

magick image.jpg -quality 85 output.jpg

Optimize PNG compression:

magick image.png -quality 95 output.png

Create high-quality WebP:

magick image.jpg -quality 90 output.webp

Thumbnails

Generate thumbnail (fast, lower quality):

magick image.jpg -thumbnail 200x200 thumb.jpg

Generate thumbnail with padding:

magick image.jpg -thumbnail 200x200 -background white -gravity center -extent 200x200 thumb.jpg

Batch Operations

Resize all images in directory:

magick mogrify -resize 800x600 -path resized/ *.jpg

Convert and resize in one operation:

magick mogrify -resize 1200x -format webp -quality 85 -path output/ *.jpg

Process specific file types:

magick mogrify -resize 50% -path smaller/ *.{jpg,png,gif}

Image Information

Display image information:

magick identify image.jpg

Detailed image information:

magick identify -verbose image.jpg

Advanced Transformations

Rotate image:

magick image.jpg -rotate 90 rotated.jpg

Flip horizontally:

magick image.jpg -flop flipped.jpg

Flip vertically:

magick image.jpg -flip flipped.jpg

Crop to specific region:

magick image.jpg -crop 800x600+100+100 cropped.jpg

Auto-orient based on EXIF:

magick image.jpg -auto-orient output.jpg

Strip metadata (reduce file size):

magick image.jpg -strip output.jpg

Important Notes

mogrify vs convert

• magick mogrify: Modifies files in-place or writes to specified path

  • Use -path option to preserve originals
  • Efficient for batch operations

• magick convert (or just magick): Creates new files

  • Always preserves original
  • Better for single-file operations

Performance Tips

1. Use -thumbnail for thumbnails: Faster than -resize for small previews
2. Use -strip to remove metadata: Reduces file size significantly
3. Batch operations: Process multiple files in one mogrify command
4. Quality settings: 85-90 is usually optimal for JPEG (balances size/quality)

Format Recommendations

• JPEG: Photos, complex images with gradients (lossy)
• PNG: Screenshots, graphics with transparency (lossless)
• WebP: Modern format, excellent compression (lossy or lossless)
• GIF: Simple animations, limited colors
• TIFF: Archival, high-quality storage

Safety Considerations

Always test commands on copies first:

# Create test directory
mkdir -p test-output

# Test on single file
magick original.jpg -resize 50% test-output/test.jpg

# Verify result before batch processing

Use -path with mogrify to preserve originals:

# This preserves originals in current directory
magick mogrify -resize 800x -path resized/ *.jpg

Quote wildcards in shell:

# Prevents premature shell expansion
magick mogrify -resize '800x600>' -path output/ '*.jpg'

Common Patterns

Web Optimization Workflow

# Create optimized versions for web
mkdir -p web-optimized

# Convert to WebP with quality 85, resize to max 1920px width
magick mogrify -resize 1920x -quality 85 -format webp -path web-optimized/ *.jpg

# Strip metadata to reduce size
magick mogrify -strip web-optimized/*.webp

Thumbnail Generation

# Create thumbnail directory
mkdir -p thumbnails

# Generate 300x300 thumbnails with white padding
for img in *.jpg; do
  magick "$img" -thumbnail 300x300 -background white -gravity center -extent 300x300 "thumbnails/${img%.jpg}_thumb.jpg"
done

Multi-Format Export

# Export to multiple formats for compatibility
mkdir -p exports/{png,webp,jpg}

for img in source/*.png; do
  name=$(basename "$img" .png)
  magick "$img" -quality 90 "exports/png/$name.png"
  magick "$img" -quality 85 "exports/webp/$name.webp"
  magick "$img" -quality 85 "exports/jpg/$name.jpg"
done

Troubleshooting

Check ImageMagick version:

magick -version

Verify supported formats:

magick identify -list format

Test command on single file first:

# Always test before batch operations
magick test-image.jpg -resize 50% test-output.jpg

When to Use This Skill

Use this skill when...	Use other skills instead when...
Converting an image between standard formats (PNG/JPG/WebP/AVIF/GIF/HEIC)	Producing a brand-new image from a text prompt — use generate-image
Resizing, compressing, or adjusting quality of an existing image	Generating a repository social preview — use github-actions-plugin:github-social-preview
Running batch processing or thumbnail generation across many files	Advanced photo editing or complex filters (use GIMP, Photoshop, or dedicated tools)
Performing basic transformations (rotate, crop, flip) at scale	Video processing (use FFmpeg) or vector graphics (use Inkscape)

Integration with Workflows

This skill complements other development workflows:

• Web development: Optimize images for deployment
• Documentation: Generate screenshots and diagrams
• CI/CD: Automate image processing in pipelines
• Content creation: Prepare images for various platforms

The magick command is typically available via Homebrew (brew install imagemagick) or system package managers.