image-files

name	Image Files
description	Image manipulation using ImageMagick command-line tools for resizing, converting, optimizing, and batch processing

Image Files

Instructions

When helping users work with image files, follow these guidelines:

1. Tool Availability: ImageMagick is installed and available on the system path. Use magick command (modern syntax) or legacy commands (convert, identify, mogrify) If it is not on the path look in C:\Program Files\ImageMagick-7.1.2-Q16-HDRI

2. Modern vs Legacy Syntax:

   • Modern (ImageMagick 7+): magick convert input.jpg output.png
   • Legacy (ImageMagick 6): convert input.jpg output.png
   • Try modern syntax first, fall back to legacy if command not found

3. Common Operations:

   • Resize: Use -resize with geometry (e.g., 800x600, 50%, 800x)
   • Convert Format: Change file extension (e.g., .jpg to .png)
   • Quality: Use -quality for JPEG compression (1-100)
   • Strip Metadata: Use -strip to remove EXIF data
   • Batch Processing: Use mogrify for in-place edits or shell loops for batch conversions

4. Preserve Aspect Ratio: Use geometry without ! suffix (e.g., 800x600 not 800x600!)

5. Output Paths: Always specify full output path to avoid overwriting originals

6. Format Support: Common formats include JPG, PNG, GIF, BMP, TIFF, WebP, PDF

7. Error Handling: Check file exists before processing, verify output was created

8. Performance: For batch operations, process files in parallel if system has multiple cores

Examples

Example 1: Resize Single Image

User: Resize this image to 800px wide, maintaining aspect ratio

Claude: I'll use ImageMagick to resize the image:
- Preserve aspect ratio with 800x geometry
- Keep original format
- Save to new filename to preserve original

magick convert input.jpg -resize 800x output.jpg

Example 2: Batch Convert and Optimize

User: Convert all PNG files to JPEG and reduce file size

Claude: I'll batch convert PNG to JPEG with optimization:
- Strip metadata with -strip
- Set quality to 85 (good balance)
- Process all PNG files in directory

for file in *.png; do magick convert "$file" -strip -quality 85 "${file%.png}.jpg"; done

Example 3: Generate Thumbnails

User: Create thumbnails for all images in a folder

Claude: I'll generate thumbnails:
- Resize to 200x200 (constrained, maintain aspect)
- Save with _thumb suffix
- Preserve format

for img in *.jpg; do magick convert "$img" -resize 200x200 "thumbs/${img%.jpg}_thumb.jpg"; done

Example 4: Get Image Information

User: What are the dimensions of this image?

Claude: I'll use identify to get image details:

magick identify input.jpg
# or: identify input.jpg

---

Reference Implementation Details

Common ImageMagick operations and patterns.

Basic Operations

Resize Images

Maintain Aspect Ratio:

# Resize to width of 800px (height auto)
magick convert input.jpg -resize 800x output.jpg

# Resize to height of 600px (width auto)
magick convert input.jpg -resize x600 output.jpg

# Resize to fit within 800x600 box
magick convert input.jpg -resize 800x600 output.jpg

# Resize to 50% of original
magick convert input.jpg -resize 50% output.jpg

Force Exact Dimensions (distorts if needed):

magick convert input.jpg -resize 800x600! output.jpg

Resize and Crop to Exact Dimensions:

# Crop to center after resize
magick convert input.jpg -resize 800x600^ -gravity center -extent 800x600 output.jpg

Convert Formats

# JPG to PNG
magick convert input.jpg output.png

# PNG to JPG with quality
magick convert input.png -quality 90 output.jpg

# Multiple formats
magick convert input.tiff output.jpg output.png

# PDF to images (one per page)
magick convert document.pdf page-%03d.jpg

Optimize Images

JPEG Optimization:

# Reduce quality (85 is good balance)
magick convert input.jpg -quality 85 output.jpg

# Strip metadata and optimize
magick convert input.jpg -strip -quality 85 output.jpg

# Progressive JPEG
magick convert input.jpg -interlace Plane -quality 85 output.jpg

PNG Optimization:

# Basic PNG optimization
magick convert input.png -strip output.png

# Reduce PNG colors (for smaller file)
magick convert input.png -colors 256 output.png

Crop and Trim

# Crop to specific region (width x height + x_offset + y_offset)
magick convert input.jpg -crop 800x600+100+50 output.jpg

# Auto-trim whitespace
magick convert input.jpg -trim output.jpg

# Add border
magick convert input.jpg -border 10x10 -bordercolor white output.jpg

Image Information

# Basic info (format, dimensions, size)
magick identify input.jpg

# Verbose info (all metadata)
magick identify -verbose input.jpg

# Just dimensions
magick identify -format "%wx%h" input.jpg

Batch Operations

Batch Resize

Using mogrify (in-place modification):

# DANGEROUS: Overwrites originals!
magick mogrify -resize 800x *.jpg

# Safer: Output to different directory
mkdir resized
magick mogrify -path resized -resize 800x *.jpg

Using loop (safer):

# Bash loop for batch resize
mkdir output
for img in *.jpg; do
  magick convert "$img" -resize 800x "output/$img"
done

# PowerShell loop
mkdir output
Get-ChildItem *.jpg | ForEach-Object {
  magick convert $_.Name -resize 800x "output/$($_.Name)"
}

Batch Convert Format

# Convert all PNG to JPG
for file in *.png; do
  magick convert "$file" -quality 90 "${file%.png}.jpg"
done

# Convert all to WebP
for file in *.jpg; do
  magick convert "$file" -quality 90 "${file%.jpg}.webp"
done

Batch Optimize

# Optimize all JPEGs in place (with backup)
mkdir originals
for img in *.jpg; do
  cp "$img" "originals/$img"
  magick convert "$img" -strip -quality 85 "$img"
done

Parallel Processing

# Process files in parallel (requires GNU parallel)
ls *.jpg | parallel magick convert {} -resize 800x output/{}

# Or using xargs (Unix/Linux)
ls *.jpg | xargs -P 4 -I {} magick convert {} -resize 800x output/{}

Advanced Operations

Watermarking

# Add text watermark
magick convert input.jpg \
  -gravity southeast \
  -pointsize 24 \
  -fill white \
  -annotate +10+10 'Copyright 2025' \
  output.jpg

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

Image Composition

# Combine images horizontally
magick convert img1.jpg img2.jpg +append output.jpg

# Combine images vertically
magick convert img1.jpg img2.jpg -append output.jpg

# Create montage/grid
magick montage *.jpg -tile 3x3 -geometry +5+5 grid.jpg

Effects and Filters

# Convert to grayscale
magick convert input.jpg -colorspace Gray output.jpg

# Blur
magick convert input.jpg -blur 0x8 output.jpg

# Sharpen
magick convert input.jpg -sharpen 0x1 output.jpg

# Rotate
magick convert input.jpg -rotate 90 output.jpg

# Flip/Flop
magick convert input.jpg -flip output.jpg    # vertical flip
magick convert input.jpg -flop output.jpg    # horizontal flip

# Sepia tone
magick convert input.jpg -sepia-tone 80% output.jpg

Background Removal

# Remove white background (make transparent)
magick convert input.jpg -fuzz 10% -transparent white output.png

# Replace background color
magick convert input.jpg -fuzz 10% -fill blue -opaque white output.jpg

Useful Patterns

Create Thumbnails with Prefix/Suffix

# Add _thumb suffix
for img in *.jpg; do
  magick convert "$img" -resize 200x200 "${img%.jpg}_thumb.jpg"
done

# Add thumb_ prefix
for img in *.jpg; do
  magick convert "$img" -resize 200x200 "thumb_$img"
done

Maintain Directory Structure

# Recursively process images, maintaining directory structure
find . -name "*.jpg" -type f | while read file; do
  dir=$(dirname "$file")
  name=$(basename "$file")
  mkdir -p "output/$dir"
  magick convert "$file" -resize 800x "output/$dir/$name"
done

Progressive Quality Outputs

# Generate multiple quality versions
for quality in 95 85 75 60; do
  magick convert input.jpg -quality $quality "output_q${quality}.jpg"
done

Generate Responsive Image Sizes

# Create common responsive sizes
for width in 320 640 768 1024 1920; do
  magick convert input.jpg -resize ${width}x "responsive/image_${width}w.jpg"
done

Error Handling and Validation

Check File Exists

if [ -f "input.jpg" ]; then
  magick convert input.jpg -resize 800x output.jpg
else
  echo "Error: input.jpg not found"
fi

Verify Output Created

magick convert input.jpg -resize 800x output.jpg
if [ -f "output.jpg" ]; then
  echo "Success: output.jpg created"
else
  echo "Error: conversion failed"
fi

Handle Spaces in Filenames

# Always quote variables
for img in *.jpg; do
  magick convert "$img" -resize 800x "output/$img"
done

Format-Specific Options

JPEG

# Quality (1-100, default 92)
-quality 85

# Sampling factor (4:2:0 for smaller files)
-sampling-factor 4:2:0

# Progressive
-interlace Plane

# Strip metadata
-strip

PNG

# Compression level (0-9, higher = smaller but slower)
-quality 95  # PNG quality is compression level

# Bit depth
-depth 8

# Remove alpha channel
-alpha off

WebP

# WebP quality
-quality 90

# Lossless WebP
-define webp:lossless=true

Common Use Cases

Prepare Images for Web

# Optimize for web: resize, strip metadata, optimize quality
magick convert input.jpg \
  -resize 1920x \
  -strip \
  -quality 85 \
  -sampling-factor 4:2:0 \
  -interlace Plane \
  output.jpg

Convert Screenshots to Optimized Format

# PNG screenshots to optimized JPEG
for png in *.png; do
  magick convert "$png" -strip -quality 90 "${png%.png}.jpg"
done

Create Social Media Images

# Facebook/Twitter cover (1200x630)
magick convert input.jpg \
  -resize 1200x630^ \
  -gravity center \
  -extent 1200x630 \
  social_cover.jpg

# Instagram square (1080x1080)
magick convert input.jpg \
  -resize 1080x1080^ \
  -gravity center \
  -extent 1080x1080 \
  instagram.jpg

Troubleshooting

ImageMagick Not Found

# Check if installed
magick --version
convert --version

# Windows: Check PATH environment variable
# Linux: sudo apt-get install imagemagick
# macOS: brew install imagemagick

Permission Denied

# Check file permissions
ls -l input.jpg

# Make readable
chmod 644 input.jpg

Out of Memory

# Limit memory usage
magick convert input.jpg -limit memory 1GB -resize 800x output.jpg

# Process in smaller batches

Policy Errors (PDF, etc.)

# Edit ImageMagick policy.xml
# Location: /etc/ImageMagick-7/policy.xml
# Remove or comment out restrictive policies for PDF, PS, etc.

Command Reference

Core Commands

• magick convert - Convert and modify images
• magick identify - Display image information
• magick mogrify - Modify images in place
• magick montage - Create composite images
• magick compare - Compare two images

Legacy Commands (ImageMagick 6)

• convert - Same as magick convert
• identify - Same as magick identify
• mogrify - Same as magick mogrify
• montage - Same as magick montage
• compare - Same as magick compare

Best Practices

1. Always backup originals before batch operations
2. Use descriptive output names to avoid confusion
3. Quote filenames to handle spaces and special characters
4. Test commands on single file before batch processing
5. Create output directories before processing
6. Use appropriate quality settings (85 is usually good for JPEGs)
7. Strip metadata to reduce file size (unless needed)
8. Maintain aspect ratio unless explicitly distorting
9. Use modern syntax (magick convert) for future compatibility
10. Check command success before continuing in scripts