📦 WebAssembly MozJPEG encoder

A dependency-free MozJPEG encoder written in WebAssembly

It encodes raw RGB(A) image data in a Uint8Array into the JPEG format.

Installation

yarn add @saschazar/wasm-mozjpeg

or

npm install --save @saschazar/wasm-mozjpeg

Usage

It supports usage in the browser, in a Web Worker and of course Node.js.

// Node.js
import wasm_mozjpeg from '@saschazar/wasm-mozjpeg';
import defaultOptions from '@saschazar/wasm-mozjpeg/options';

// Web Worker - see: https://developer.mozilla.org/en-US/docs/Web/API/WorkerGlobalScope/importScripts
importScripts('wasm_mozjpeg.js');

// -------- Browser/Web Worker/Node.js code below --------

// Load raw RGB image data in Uint8Array (e.g. consistently chained [R][G][B] data)
const array = new Uint8Array(['some', 'raw', 'RGB', 'image', 'data']);
const channels = 3; // 3 for RGB, 4 for RGBA (must adapt options.in_color_space!)
const width = 800; // the image's width
const height = 600; // the image's height
const options = defaultOptions; // MozJPEG's options, complete object crucially needed!
options.in_color_space = 6; // 6 for RGB, 12 for RGBA, see J_COLOR_SPACE in wasm_mozjpeg.d.ts
let result;

// Initialize the WebAssembly Module
const mozjpegModule = wasm_mozjpeg({
  onRuntimeInitialized() {
    result = mozjpegModule.encode(array, width, height, channels, options); // encode image data and return a new Uint8Array
    mozjpegModule.free(); // clean up memory after encoding is done
  },
});

Example

A working example is available on RunKit.

Options

⚠️ It's crucial to provide a full options object. The default options object may be imported from the options.js file.

Also take a close look at the in_color_space property, if an image Buffer containing an alpha channel is provided! (e.g. RGBA data from <canvas />). The J_COLOR_SPACE enum in wasm_mozjpeg.d.ts contains all the valid numeric values for the respective in_color_space and out_color_space properties.

Credits

This module uses the mozilla/mozjpeg's source code and most of the code is written according to the examples provided in that repository.

License

Licensed under the MIT license.

Copyright ©️ 2020—2021 Sascha Zarhuber