CharLS WebAssembly

CharLS WebAssembly is a WebAssembly build of CharLS, a high-performance JPEG-LS codec library. This package provides JavaScript/TypeScript bindings for encoding and decoding JPEG-LS images in both Node.js and browser environments.

This project was originally forked from charls-js, created by Chris Hafey. It has been updated to use Wasm 3.0 and the latest version of CharLS.

Installation

npm install @team-charls/charls-wasm

Quick Start

Decoding a JPEG-LS Image

import { createJpegLSDecoder } from '@team-charls/charls-wasm'

// Typical pattern is to re-use decoder instances for better performance.
const decoder = await createJpegLSDecoder()

function decodeImage (sourceBuffer) {
  const destinationBuffer = decoder.decode(sourceBuffer)

  console.log('Frame info:', decoder.getFrameInfo())
  console.log('Interleave mode:', decoder.getInterleaveMode())
  console.log('Near lossless:', decoder.getNearLossless())

  return destinationBuffer
}

Encoding to JPEG-LS

import { createJpegLSEncoder } from '@team-charls/charls-wasm'

// Typical pattern is to re-use encoder instances for better performance.
const encoder = await createJpegLSEncoder()

function encodeImageLossless (pixelBuffer, frameInfo) {
  const destinationBuffer = encoder.encode(pixelBuffer,
    frameInfo.width,
    frameInfo.height,
    frameInfo.bitsPerSample,
    frameInfo.componentCount,
    0, // Interleave mode (0 = none, 1 = line, 2 = sample)
    0, // Encoding options bitmask (0=none, 1=evenSize, 2=includeVersion, 4=includePCParametersJAI)
    0 // NEAR parameter (0 = lossless, >0 = near-lossless)
  )

  return destinationBuffer
}

API Reference

Factory Functions

• createJpegLSDecoder() - Creates a new decoder instance (async)
• createJpegLSEncoder() - Creates a new encoder instance (async)
• initializeModule() - Explicitly initialize the WASM module (optional, called automatically)

Classes

• JpegLSDecoder - Decoder class for advanced usage
• JpegLSEncoder - Encoder class for advanced usage
• JpegLSError - Custom error class for JPEG-LS operations

Supported Platforms

All environments that can run Wasm 3.0 modules are supported:

• Browsers: Chrome/Edge 137+, Firefox 131+, Safari 26.2+
• Node.js: 18.0+

Examples

For complete examples, see:

• Browser example
• Node.js example

Resources

• GitHub Repository
• CharLS C++ Library
• Live Demo
• API Documentation

License

BSD-3-Clause - See LICENSE.md