Stealth Watermark 🔐

A robust library for digital image watermarking using Discrete Wavelet Transform (DWT) and Quantization Index Modulation (QIM).

Features

• Robust Watermarking: DWT + QIM algorithm for maximum resistance
• Multi-Channel: Support for individual RGB channels
• Configurable Parameters: Adjustable quantization and redundancy
• High Performance: Optimized for large images
• Cross-Platform: Works on Node.js, browser, and edge environments
• TypeScript: Complete type definitions included
• Test Coverage: Comprehensive test suite for guaranteed quality

Installation

npm install stealth-watermark

📖 Quick Start

Adding Watermark

import { addWatermark, extractWatermark } from 'stealth-watermark';
import { readFileSync, writeFileSync } from 'fs';

// Read the original image
const originalImage = readFileSync('input.png');

// Add watermark
const { image: watermarkedImage } = await addWatermark(originalImage, "Secret message", {
  channel: 0,    // Red channel (0=R, 1=G, 2=B)
  q: 12,         // Quantization step (higher = more robust)
  seed: 1234,    // Seed for permutation (same for extraction)
  reps: 3        // Redundancy for robustness (recommended: 3)
});

// Save the watermarked image
writeFileSync('watermarked.png', watermarkedImage);

Extracting Watermark

// Extract the watermark
const extractedMessage = await extractWatermark(watermarkedImage, {
  channel: 0,    // Same channel used for insertion
  q: 12,         // Same quantization step
  seed: 1234,    // Same seed
  reps: 3        // Same redundancy
});

console.log('Extracted message:', extractedMessage);
// Output: Secret message

API Reference

addWatermark(imageBuffer, watermarkText, options)

Inserts an invisible watermark into an image.

Parameters:

• imageBuffer: Buffer - Original image buffer
• watermarkText: string - Text to hide
• options: WatermarkOptions - Configuration options

Options:

interface WatermarkOptions {
  channel?: 0 | 1 | 2;     // Color channel (default: 0)
  q?: number;               // Quantization step (default: 12)
  seed?: number;            // Permutation seed (default: 1234)
  reps?: number;            // Redundancy (default: 3)
}

Returns:

Promise<WatermarkResult> {
  image: Buffer;  // Image with watermark
}

extractWatermark(imageBuffer, options)

Extracts a watermark from an image.

Parameters:

• imageBuffer: Buffer - Image buffer with watermark
• options: WatermarkOptions - Same options used for insertion

Returns:

Promise<string>  // Extracted text

Advanced Examples

Multi-Channel Watermarking

// Insert watermark in all channels
const channels = [0, 1, 2]; // R, G, B
const messages = ['Red', 'Green', 'Blue'];

for (let i = 0; i < channels.length; i++) {
  const { image } = await addWatermark(
    originalImage, 
    messages[i], 
    { channel: channels[i], q: 8, seed: 1234 + i }
  );
  originalImage = image; // Use output as input for next
}

Robust Configuration

// Configuration for maximum robustness
const robustOptions = {
  channel: 0,
  q: 16,        // Higher quantization
  seed: 9999,   // Custom seed
  reps: 5,      // Higher redundancy
};

const { image } = await addWatermark(originalImage, "Important message", robustOptions);

Error Handling

try {
  const message = await extractWatermark(imageBuffer, options);
  console.log('Extracted watermark:', message);
} catch (error) {
  if (error.message.includes('Invalid watermark length')) {
    console.error('Extraction parameters are incorrect');
  } else if (error.message.includes('Insufficient capacity')) {
    console.error('Image too small for watermark');
  } else {
    console.error('Extraction error:', error.message);
  }
}

How It Works

1. Discrete Wavelet Transform (DWT)

• Decomposes image into frequency bands
• Uses HL band (High-Low) for watermarking
• Maintains visual quality of the image

2. Quantization Index Modulation (QIM)

• Quantizes coefficients into distinct buckets
• Bit 0 → lower bucket (0.25q)
• Bit 1 → upper bucket (0.75q)

3. Redundancy and Permutation

• Repeats each bit multiple times (default: 3x)
• Uses seed-based permutation for security
• Majority voting for robustness

4. Inverse DWT (IDWT)

• Reconstructs image with watermark
• Maintains original structure
• Watermark invisible to human eye

📊 Performance

• Speed: ~100ms for 1024x1024 image
• Capacity: ~1KB for 512x512 image
• Robustness: Resists JPEG compression (90% quality)
• Memory: Optimized for large images

Testing

# Run all tests
npm test

# Test in watch mode
npm run test:watch

# Test with coverage
npm run test:coverage

🛠️ Development

Local Setup

# Clone repository
git clone https://github.com/sergioska/stealth-watermark.git
cd stealth-watermark

# Install dependencies
npm install

# Build project
npm run build

# Run tests
npm test

Available Scripts

• npm run build - Compile TypeScript
• npm run test - Run test suite
• npm run lint - Check code with ESLint
• npm run format - Format code with Prettier

🤝 Contributing

Contributions are welcome! To contribute:

1. Fork the repository
2. Create a feature branch (git checkout -b feature/AmazingFeature)
3. Commit your changes (git commit -m 'Add AmazingFeature')
4. Push to the branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

License

This project is released under the MIT license. See LICENSE for details.

Acknowledgments

• DWT Algorithm: Based on Haar wavelet transform
• QIM Implementation: Quantization Index Modulation for robustness
• Image Processing: Uses Jimp and pngjs libraries

Support

• Issues: GitHub Issues
• Documentation: Wiki
• Discussions: GitHub Discussions

---

⭐ If this project is useful to you, consider giving it a star on GitHub!