imagemagick-conversion（图像魔术转换）

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

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.