Skill: Screenshot Compression

Compress screenshot images (PNG/JPEG) in place while keeping the original format. Uses pngquant for PNG and jpegoptim for JPEG — both are highly effective for screenshot content (UI elements, text, flat colors).

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

The user has screenshot files that are too large and wants to reduce file size without changing format. Common scenarios:

• 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)

WebP has better compression, but poor compatibility in some contexts:

Context

WebP Support

Browsers (Chrome/Firefox/Safari/Edge)

Yes

GitHub Issues/PRs

Yes

WeChat editor

No

Word / PowerPoint

No

Some forums/blog backends

Varies

Keeping PNG/JPEG ensures the compressed images work everywhere.

Default Workflow

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

The script will:

• Check that pngquant and jpegoptim are installed — if not, print install instructions and exit

• Auto-detect file format by extension

• Compress each file in place (overwrites the original)

• Print per-file and total compression summary

Dependency Check

The script requires two system tools. If either is missing, it exits with install instructions instead of proceeding. Do not install them on behalf of the user — just relay the error message so the user can install them.

Install commands:

# macOS

brew install pngquant jpegoptim

# Ubuntu / Debian

sudo apt install pngquant jpegoptim

# CentOS / RHEL

sudo yum install pngquant jpegoptim

Script Options

Flag

Default

Description

paths (positional)

required

Image files or directories to compress

-r, --recursive

off

Recursively process directories

--png-quality

80-95

pngquant quality range (min-max, 0-100)

--jpeg-quality

85

jpegoptim max quality (0-100)

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

Scenario

--png-quality

--jpeg-quality

General screenshots (docs, web pages)

80-95

85

Code screenshots (need sharp text)

90-100

90

Thumbnails / previews (size priority)

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.