image-manipulation-image-magick

Image Manipulation with ImageMagick

This skill enables image processing and manipulation tasks using ImageMagick across Windows, Linux, and macOS systems.

When to Use This Skill

Use this skill when you need to:

• Resize images (single or batch)
• Get image dimensions and metadata
• Convert between image formats
• Create thumbnails
• Process wallpapers for different screen sizes
• Batch process multiple images with specific criteria

Prerequisites

• ImageMagick installed on the system
• Windows: PowerShell with ImageMagick available as magick (or at C:\Program Files\ImageMagick-*\magick.exe)
• Linux/macOS: Bash with ImageMagick installed via package manager (apt, brew, etc.)

Execution Scope

This skill generates shell commands that use the following executables. For safe operation, ensure the execution environment restricts shell access to only these commands:

No network access, privilege escalation, or writes outside the explicitly specified output paths are performed.

Core Capabilities

1. Image Information

• Get image dimensions (width x height)
• Retrieve detailed metadata (format, color space, etc.)
• Identify image format

2. Image Resizing

• Resize single images
• Batch resize multiple images
• Create thumbnails with specific dimensions
• Maintain aspect ratios

3. Batch Processing

• Process images based on dimensions
• Filter and process specific file types
• Apply transformations to multiple files

Usage Examples

Example 0: Resolve magick executable

PowerShell (Windows):

# Prefer ImageMagick on PATH
$magick = (Get-Command magick -ErrorAction SilentlyContinue)?.Source

# Fallback: common install pattern under Program Files
if (-not $magick) {
    $magick = Get-ChildItem "C:\\Program Files\\ImageMagick-*\\magick.exe" -ErrorAction SilentlyContinue |
        Select-Object -First 1 -ExpandProperty FullName
}

if (-not $magick) {
    throw "ImageMagick not found. Install it and/or add 'magick' to PATH."
}

Bash (Linux/macOS):

# Check if magick is available on PATH
if ! command -v magick &> /dev/null; then
    echo "ImageMagick not found. Install it using your package manager:"
    # The following lines are informational only — echo prints installation hints, not executed commands
    # aguara:ignore EXTDL_011 — informational echo string, not an executed install command
    echo "  Ubuntu/Debian: sudo apt install imagemagick"
    # aguara:ignore EXTDL_011 — informational echo string, not an executed install command
    echo "  macOS: brew install imagemagick"
    exit 1
fi

Example 1: Get Image Dimensions

PowerShell (Windows):

# For a single image
& $magick identify -format "%wx%h" path/to/image.jpg

# For multiple images
Get-ChildItem "path/to/images/*" | ForEach-Object { 
    $dimensions = & $magick identify -format "%f: %wx%h`n" "$($_.FullName)"
    Write-Host $dimensions 
}

Bash (Linux/macOS):

# For a single image
magick identify -format "%wx%h" path/to/image.jpg

# For multiple images
for img in path/to/images/*; do
    magick identify -format "%f: %wx%h\n" "$img"
done

Example 2: Resize Images

PowerShell (Windows):

# Resize a single image
& $magick input.jpg -resize 427x240 output.jpg

# Batch resize images
Get-ChildItem "path/to/images/*" | ForEach-Object { 
    & $magick "$($_.FullName)" -resize 427x240 "path/to/output/thumb_$($_.Name)"
}

Bash (Linux/macOS):

# Resize a single image
magick input.jpg -resize 427x240 output.jpg

# Batch resize images
for img in path/to/images/*; do
    filename=$(basename -- "$img")
    magick "$img" -resize 427x240 "path/to/output/thumb_$filename"
done

Example 3: Get Detailed Image Information

PowerShell (Windows):

# Get verbose information about an image
& $magick identify -verbose path/to/image.jpg

Bash (Linux/macOS):

# Get verbose information about an image
magick identify -verbose path/to/image.jpg

Example 4: Process Images Based on Dimensions

PowerShell (Windows):

Get-ChildItem "path/to/images/*" | ForEach-Object { 
    $dimensions = & $magick identify -format "%w,%h" "$($_.FullName)"
    if ($dimensions) {
        $width,$height = $dimensions -split ','
        if ([int]$width -eq 2560 -or [int]$height -eq 1440) {
            Write-Host "Processing $($_.Name)"
            & $magick "$($_.FullName)" -resize 427x240 "path/to/output/thumb_$($_.Name)"
        }
    }
}

Bash (Linux/macOS):

for img in path/to/images/*; do
    dimensions=$(magick identify -format "%w,%h" "$img")
    if [[ -n "$dimensions" ]]; then
        width=$(echo "$dimensions" | cut -d',' -f1)
        height=$(echo "$dimensions" | cut -d',' -f2)
        if [[ "$width" -eq 2560 || "$height" -eq 1440 ]]; then
            filename=$(basename -- "$img")
            echo "Processing $filename"
            magick "$img" -resize 427x240 "path/to/output/thumb_$filename"
        fi
    fi
done

Guidelines

1. Always quote file paths — Use quotes around file paths that might contain spaces. In PowerShell, always use "$($_.FullName)" (not bare $_.FullName) when passing pipeline objects to external programs via &. In Bash, always double-quote variables ("$img").
2. Use the -- option terminator in Bash — Use basename -- "$img" to prevent filenames beginning with - from being misinterpreted as flags by basename. For magick, glob expansions from patterns like path/to/images/* always produce paths with a directory prefix, but explicit validation is advisable for untrusted input.
3. Use the & operator (PowerShell) - Invoke the magick executable using & in PowerShell
4. Store the path in a variable (PowerShell) - Assign the ImageMagick path to $magick for cleaner code
5. Wrap in loops - When processing multiple files, use ForEach-Object (PowerShell) or for loops (Bash)
6. Verify dimensions first - Check image dimensions before processing to avoid unnecessary operations
7. Use appropriate resize flags - Consider using ! to force exact dimensions or ^ for minimum dimensions
8. Validate untrusted input — If processing files from an untrusted source, validate or sanitize filenames before passing them to magick. In particular, reject or skip filenames containing @ or % characters, which ImageMagick treats as special directives (read-from-file and format substitution respectively), as quoting alone does not neutralise these.

Common Patterns

PowerShell Patterns

Pattern: Store ImageMagick Path

$magick = (Get-Command magick).Source

Pattern: Get Dimensions as Variables

$dimensions = & $magick identify -format "%w,%h" "$($_.FullName)"
$width,$height = $dimensions -split ','

Pattern: Conditional Processing

if ([int]$width -gt 1920) {
    & $magick "$($_.FullName)" -resize 1920x1080 "$outputPath"
}

Pattern: Create Thumbnails

& $magick "$($_.FullName)" -resize 427x240 "thumbnails/thumb_$($_.Name)"

Bash Patterns

Pattern: Check ImageMagick Installation

command -v magick &> /dev/null || { echo "ImageMagick required"; exit 1; }

Pattern: Get Dimensions as Variables

dimensions=$(magick identify -format "%w,%h" "$img")
width=$(echo "$dimensions" | cut -d',' -f1)
height=$(echo "$dimensions" | cut -d',' -f2)

Pattern: Conditional Processing

if [[ "$width" -gt 1920 ]]; then
    magick "$img" -resize 1920x1080 "$outputPath"
fi

Pattern: Create Thumbnails

filename=$(basename -- "$img")
magick "$img" -resize 427x240 "thumbnails/thumb_$filename"

Limitations

• Large batch operations may be memory-intensive
• Some complex operations may require additional ImageMagick delegates
• On older Linux systems, use convert instead of magick (ImageMagick 6.x vs 7.x)