@abasb75/charls

A JavaScript/TypeScript package built on top of the CharLS reference implementation, providing full client-side JPEG-LS encoding and decoding capabilities using WebAssembly (charls 2.4.2).

Perfect for web applications that need lossless or near-lossless image compression (e.g., DICOM viewers, medical imaging tools, or any project dealing with high-fidelity image data).

Demo

JLS Converter — Lossless Compression Tool

Installation
Bash

``bash
npm install @abasb75/charls

`

How to use

Your project must support ES modules (e.g., Vite, Webpack, Next.js, etc.).
The bundler should correctly handle WASM files (using ?url import is required).
Usage
Required Imports

`typescript

import CharLSDecoder from "@abasb75/charls/decode";
import CharLSEncoder from "@abasb75/charls/encode";
import decoderUrl from "@abasb75/charls/jls_decoder.wasm?url";
import encoderUrl from "@abasb75/charls/jls_encoder.wasm?url";

let decoderInstance: any = null;
let encoderInstance: any = null;
let decodeFn: any = null;
let encodeFn: any = null;

async function decodeAndReencode(pixelData: DataView): Promiseuint8array {
// Load decoder if not already loaded
if (!decoderInstance) {
decoderInstance = await CharLSDecoder({
locateFile: () => new URL(decoderUrl, import.meta.url).href
});
decodeFn = decoderInstance.decode;
}

// Load encoder if not already loaded
if (!encoderInstance) {
encoderInstance = await CharLSEncoder({
locateFile: () => new URL(encoderUrl, import.meta.url).href
});
encodeFn = encoderInstance.encode;
}

const buffer = new Uint8Array(pixelData.buffer, pixelData.byteOffset, pixelData.byteLength);

// Decode
const decoded = await decodeFn(buffer);

// Re-encode (useful for validation)
const encoded = await encodeFn(
decoded.data,
decoded.width,
decoded.height,
decoded.components,
decoded.bitsPerSample,
decoded.interleave_mode,
decoded.nearLossless || 0
);

// Decode again to get final pixel data
const final = await decodeFn(encoded.data);

return final.data;
}
`

Javascript

`html



``