Skill: Screenshot Compression

pngquant

jpegoptim

Prerequisites:

pngquant

and

jpegoptim

must be installed on the system. The script will not install them automatically — it checks for their presence and prints install instructions if missing.

When to Use

• Preparing images for GitHub READMEs, blog posts, or documentation
• Reducing image sizes before committing to a repository
• Batch compressing a directory of screenshots

Why Keep Original Format (Not WebP)

Default Workflow

python /path/to/skills/screenshot-compression/scripts/compress_screenshots.py <files-or-directories>

1. Check that

   pngquant

   and

   jpegoptim

   are installed — if not, print install instructions and exit
2. Auto-detect file format by extension
3. Compress each file in place (overwrites the original)
4. Print per-file and total compression summary

Dependency Check

# macOS
brew install pngquant jpegoptim

# Ubuntu / Debian
sudo apt install pngquant jpegoptim

# CentOS / RHEL
sudo yum install pngquant jpegoptim

Script Options

paths

-r

--recursive

--png-quality

80-95

--jpeg-quality

85

Examples

# Compress a single file
python .../compress_screenshots.py screenshot.png

# Compress all images in a directory
python .../compress_screenshots.py ./images/

# Recursive directory scan
python .../compress_screenshots.py ./docs/ --recursive

# High quality for code screenshots
python .../compress_screenshots.py *.png --png-quality 90-100

# Aggressive compression for thumbnails
python .../compress_screenshots.py *.jpg --jpeg-quality 70

Quality Tuning Guide

--png-quality

--jpeg-quality

80-95

85

90-100

90

60-80

70

How It Works

PNG (pngquant)

• Quantizes 24-bit true color (16M colors) down to an 8-bit palette (256 colors)
• Uses Floyd-Steinberg dithering for smooth gradients
• Screenshots are ideal candidates — UI colors are typically well under 256 unique values
• Typical reduction: 60-80%

JPEG (jpegoptim)

• Re-encodes at the specified quality level
• Strips metadata (EXIF, ICC profiles, thumbnails) via

  --strip-all

• Optimizes Huffman tables
• Typical reduction: 20-50%

Important Notes

• Files are compressed in place — the original is overwritten. Back up files first if needed.
• Only

  .png

  ,

  .jpg

  , and

  .jpeg

  files are processed. Other formats are silently skipped.
• The script never installs dependencies. If tools are missing, it prints install instructions and exits.