A modern web app for high-quality grayscale image conversion and batch processing, built with FastAPI (Python backend) and a responsive JavaScript frontend.

• Single & Batch Image Conversion: Convert one or many images at once.
• Advanced Grayscale Modes: Choose from Rec. 709, Lab*, HSL, HSV, and more.
• High Bit Depth Support: 8, 16-bit output for maximum quality.
• Format Options: PNG, JPEG, HEIC, TIFF, WEBP, BMP.
• Chroma Subsampling & Quality Controls: Always defaults to best quality (4:4:4, quality=100).
• Preserve Transparency: Optionally keep alpha channels.
• Metadata Handling: Option to strip or preserve EXIF/ICC/DPI.
• Live Preview: See before/after instantly in the browser.
• No Image Uploads Required: All processing is local to your server.

python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt
npm install  # for Tailwind CSS (optional, for development)

npm run build:css

uvicorn main:app --reload --port 8001

Then open http://localhost:8001 in your browser.

• main.py — FastAPI backend (image processing, API endpoints)
• static/ — JS, CSS, and assets
• templates/ — HTML templates (Jinja2)
• requirements.txt — Python dependencies
• package.json, tailwind.config.js — Frontend build config
• temp_output/ — Temporary output files (auto-created)

If you see an error like OS file watch limit reached or similar when running the server with --reload, you may need to increase the file watch limit on your system.

echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p

• If you see errors about file watching on Windows, try running VS Code or your terminal as Administrator.
• For WSL, use the Linux command above inside your WSL terminal.
• If using Python's watchdog or similar, you may need to install the Windows C++ build tools or update your Python environment.
• If issues persist, consider disabling --reload or reducing the number of watched files.

• Requires pillow-heif (Python) and system libraries (libheif).
• On Linux, install libheif-dev via your package manager (e.g., sudo apt install libheif-dev).
• On Windows, use pre-built wheels for pillow-heif or see the pillow-heif documentation for Windows support.

MIT