IDWatermark

A modern library for creating holographic watermarks in images using OffscreenCanvas. Perfect for document protection, digital certificates, or any image requiring a holographic watermark effect.

Spanish: Read here.

Features

• ✨ Customizable holographic effects
• 🎨 Full control over colors and gradients
• 🖼️ Support for multiple image formats
• 🚀 Optimized performance with OffscreenCanvas
• 👷 Web Workers compatible
• 🔄 Asynchronous processing

Installation

npm install @videsk/id-watermark

Basic Usage

import IDWatermark from '@videsk/id-watermark';

const watermarker = new IDWatermark();

// Process an image
const imageBlob = await fetch('image.jpg').then(r => r.blob());
const watermarkedBlob = await watermarker.addWatermark(imageBlob, 'CONFIDENTIAL');

Configuration

The library accepts the following configuration options:

const watermarker = new IDWatermark({
  fontSize: 12,          // Font size
  fontFamily: 'Courier New', // Font family
  opacity: 1,           // Watermark opacity (0-1)
  baseHue: 270,         // Base color (0-360)
  hueStep: 3,           // Color increment between characters
  grayscale: false,     // Convert image to grayscale
  bitmapOptions: {}     // Options for createImageBitmap
});

Understanding Hue Values

The holographic effect is based on HSL (Hue, Saturation, Lightness) color space manipulation. The hue parameter determines the base color and its progression:

baseHue (0-360)

The baseHue value represents the initial color in the chromatic circle:

• 0/360: Red
• 60: Yellow
• 120: Green
• 180: Cyan
• 240: Blue
• 270: Violet (default value)
• 300: Magenta

hueStep

The hueStep controls how much the color changes between consecutive characters:

• Low values (1-5): Smooth and gradual changes
• Medium values (5-15): Moderate rainbow effect
• High values (15+): Dramatic color changes

Combination Examples

// Subtle holographic effect in violet tones
const subtleHolographic = new IDWatermark({
  baseHue: 270,
  hueStep: 3
});

// Vibrant rainbow effect
const rainbowEffect = new IDWatermark({
  baseHue: 0,
  hueStep: 15
});

// Blue monochromatic effect
const blueMonochrome = new IDWatermark({
  baseHue: 240,
  hueStep: 1
});

API

Main Methods

addWatermark(imageInput, watermarkText, encodeOptions)

Adds a watermark to an image.

const result = await watermarker.addWatermark(
  imageBlob,
  'CONFIDENTIAL',
  { type: 'image/jpeg', quality: 0.9 }
);

Parameters

• imageInput: File | Blob | ImageData | ImageBitmap | OffscreenCanvas | VideoFrame | HTMLImageElement
• watermarkText: string
• encodeOptions: Object (optional)
  • type: string (e.g., 'image/jpeg', 'image/png')
  • quality: number (0-1)

Configurable Properties

All properties can be modified at runtime:

watermarker.fontSize = 24;
watermarker.opacity = 0.7;
watermarker.baseHue = 180;

Web Workers Usage (Conceptual Example)

// main.js
const worker = new Worker('watermark.worker.js', { type: 'module' });

// Send task to worker
worker.postMessage({
  type: 'ADD_WATERMARK',
  payload: {
    image: imageBlob,
    text: 'CONFIDENTIAL',
    options: { baseHue: 270, hueStep: 3 }
  }
}, [imageBlob]);

// Receive result
worker.onmessage = (e) => {
  if (e.data.type === 'WATERMARK_COMPLETE') {
    const watermarkedBlob = e.data.payload;
    // Use the resulting blob
  }
};

Browser Compatibility

• Modern browsers with OffscreenCanvas support
• Chrome 69+
• Firefox 79+
• Edge 79+
• Safari 16.4+

License

MIT