LightLink

Each frame contains calibration markers, transfer ID, frame number, total frame count, data length, payload length, filename metadata, and CRC32 checksum.

The receiver detects the four markers, calculates a perspective transform, samples the 64 × 64 cells, reconstructs the bytes and validates CRC32.

The system does not use QR codes. The payload itself is represented by physical black/white cells.

🔒 Privacy & Security Your data is transferred locally through optical communication. No internet connection, server, cloud service, or external API is used. All data transfer happens only between the sender screen and receiver camera on your device.

📱 Progressive Web App This application works as a PWA. You can install it on your device and use it completely offline. No backend, no cloud, no external services.

📷 Camera Permission Camera access depends on browser security rules. If opening index.html directly with file:// protocol does not allow camera access, run the same file through a local server such as python -m http.server 8000 or similar. The application itself still requires no internet connection.

🔄 How It Works Sender: Converts text or files into binary data, splits into frames, adds CRC32 checksums, renders each frame as a 64×64 grid of black/white cells with calibration markers, and displays them sequentially on screen.

Receiver: Uses device camera to capture frames, detects calibration markers, calculates perspective transform, samples the binary grid, validates CRC32, reconstructs original data, and allows download of files or display of text.

💾 File Transfer Files are transferred as binary data without Base64 encoding overhead. Each file retains its original filename, MIME type, and binary content. Large files are split across multiple frames with CRC32 validation for each frame.

⚙️ Technical Details Protocol: Custom frame-based protocol with magic bytes, version, transfer ID, frame numbering, total frame count, data length, filename metadata, and CRC32 checksum.

Grid: 64 × 64 cells with four 8×8 calibration markers in corners for perspective detection.

Redundancy: Supports out-of-order frames, duplicate detection, and missing frame identification.

Error Detection: CRC32 on every frame ensures data integrity.

📊 Transfer Modes Fast (500 ms/frame): Quick transfer but requires steady camera positioning.
Normal (1000 ms/frame): Balanced speed and reliability (recommended).
Reliable (1800 ms/frame): Slower but more robust for poor lighting or camera shake.

⚠️ Limitations Camera access requires HTTPS or localhost. File:// protocol may not allow camera access in most browsers due to security restrictions. Maximum reliable transfer distance: approximately 30-50 cm depending on display and camera quality. Lighting conditions affect frame detection accuracy.