Imagemagick Conversion

---
created: 2025-12-16
modified: 2026-05-09
reviewed: 2025-12-16
name: imagemagick-conversion
description: "ImageMagick image manipulation: format conversion, resizing, batch processing, quality. Use when converting, resizing, batch-processing, or generating thumbnails."
user-invocable: false
allowed-tools: Bash, Read, Grep, Glob
model: sonnet
---

# 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:**
```bash
magick input-file [options] output-file
```

## Common Use Cases

### Format Conversion

**Basic format conversion:**
```bash
magick image.jpg image.png
magick photo.png photo.webp
```

**Batch convert all JPEGs to PNG:**
```bash
magick mogrify -format png *.jpg
```

**Convert with specific output directory:**
```bash
mkdir -p output
magick mogrify -format webp -path output/ *.jpg
```

### Resizing Images

**Resize by percentage:**
```bash
magick image.jpg -resize 50% output.jpg
```

**Resize to specific width (maintain aspect ratio):**
```bash
magick image.jpg -resize 800x output.jpg
```

**Resize to specific height (maintain aspect ratio):**
```bash
magick image.jpg -resize x600 output.jpg
```

**Resize to fit within dimensions (maintain aspect ratio):**
```bash
magick image.jpg -resize 800x600 output.jpg
```

**Resize to exact dimensions (ignore aspect ratio):**
```bash
magick image.jpg -resize 800x600! output.jpg
```

**Resize only if larger:**
```bash
magick image.jpg -resize '800x600>' output.jpg
```

**Resize only if smaller:**
```bash
magick image.jpg -resize '800x600<' output.jpg
```

### Quality and Compression

**Set JPEG quality (1-100, default 92):**
```bash
magick image.jpg -quality 85 output.jpg
```

**Optimize PNG compression:**
```bash
magick image.png -quality 95 output.png
```

**Create high-quality WebP:**
```bash
magick image.jpg -quality 90 output.webp
```

### Thumbnails

**Generate thumbnail (fast, lower quality):**
```bash
magick image.jpg -thumbnail 200x200 thumb.jpg
```

**Generate thumbnail with padding:**
```bash
magick image.jpg -thumbnail 200x200 -background white -gravity center -extent 200x200 thumb.jpg
```

### Batch Operations

**Resize all images in directory:**
```bash
magick mogrify -resize 800x600 -path resized/ *.jpg
```

**Convert and resize in one operation:**
```bash
magick mogrify -resize 1200x -format webp -quality 85 -path output/ *.jpg
```

**Process specific file types:**
```bash
magick mogrify -resize 50% -path smaller/ *.{jpg,png,gif}
```

### Image Information

**Display image information:**
```bash
magick identify image.jpg
```

**Detailed image information:**
```bash
magick identify -verbose image.jpg
```

### Advanced Transformations

**Rotate image:**
```bash
magick image.jpg -rotate 90 rotated.jpg
```

**Flip horizontally:**
```bash
magick image.jpg -flop flipped.jpg
```

**Flip vertically:**
```bash
magick image.jpg -flip flipped.jpg
```

**Crop to specific region:**
```bash
magick image.jpg -crop 800x600+100+100 cropped.jpg
```

**Auto-orient based on EXIF:**
```bash
magick image.jpg -auto-orient output.jpg
```

**Strip metadata (reduce file size):**
```bash
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:**
```bash
# 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:**
```bash
# This preserves originals in current directory
magick mogrify -resize 800x -path resized/ *.jpg
```

**Quote wildcards in shell:**
```bash
# Prevents premature shell expansion
magick mogrify -resize '800x600>' -path output/ '*.jpg'
```

## Common Patterns

### Web Optimization Workflow

```bash
# 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

```bash
# 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

```bash
# 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:**
```bash
magick -version
```

**Verify supported formats:**
```bash
magick identify -list format
```

**Test command on single file first:**
```bash
# 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.