Image Optimization Skill

Optimize and convert images for various use cases using sharp-cli.

Tools

• sharp-cli — Primary tool for all image optimization (JPEG/PNG/WebP/AVIF). Run sharp --help for full reference.
• heif-convert — Convert HEIC/HEIF to JPEG first, then use sharp for further optimization.

Workflow

1. Analyze Input

Determine what images to process:

• Check for specific files or glob pattern (e.g., *.HEIC, *.jpg)
• List matching files to confirm scope
• Detect formats and sizes if helpful

2. Analyze Reference Image (Optional)

If matching a reference image:

file reference.webp      # Get format and dimensions
ls -lah reference.webp   # Get file size

Extract: format, dimensions (width x height), approximate file size.

3. Determine Parameters

Ask user for unclear parameters. Smart defaults by use case:

Presets:

Parameters:

• Format: jpg, png, webp, avif (default: jpg for photos)
• Resolution: max dimension in pixels (default: 2560)
• Quality: 1-100 (default: 90 standard, 78 web)
• Progressive: JPEG only (default: web only)
• Mozjpeg: better compression (default: true for JPEG)
• Chroma: 4:2:0 (smaller) vs 4:4:4 (higher quality)
• Metadata: preserve EXIF (default: true unless web)
• Output: directory or in-place (default: ask if unclear)

4. Handle HEIC/HEIF Conversion

Convert HEIC/HEIF to JPEG first:

for f in *.HEIC *.heic; do
  [[ -f "$f" ]] || continue
  heif-convert -q 90 "$f" "${f%.*}.jpg"
done

Then process resulting JPEGs with sharp.

5. Build Sharp Command

Structure: sharp -i <input> -o <output-dir> [options] [resize <w> <h>]

Key options:

Examples:

# Web-optimized
sharp -i *.jpg -o ./optimized resize 1920 1920 --fit inside -q 78 -p --mozjpeg

# Standard with metadata
sharp -i *.jpg -o ./ resize 2560 2560 --fit inside -q 90 --mozjpeg -m

# High quality
sharp -i *.jpg -o ./ resize 3500 3500 --fit inside -q 90 --chromaSubsampling '4:4:4' -m

# Convert to WebP
sharp -i *.jpg -o ./webp -f webp resize 1920 1920 --fit inside -q 80

# Match reference (2200x980 webp)
sharp -i input.png -o . -f webp -q 80 resize 2200 980

6. Execute and Verify

• Show command before executing
• Run and report results (files processed, size reduction)
• Handle errors gracefully

Notes

• Always prefer sharp-cli over cwebp, imagemagick, etc.
• Use --fit inside for resize to maintain aspect ratio
• Web: progressive, mozjpeg, quality 75-85
• Archival: quality 90-95, metadata, 4:4:4 chroma
• Default to non-destructive (new directory) unless user wants in-place
• Match reference: use file for dimensions/format, ls -lah for size