@cornerstonejs/codec-libjxl

JavaScript/WebAssembly build of libjxl with separate decoder and encoder modules for JPEG XL DICOM images.

Installing

Using npm:

npm install @cornerstonejs/codec-libjxl

Using yarn:

yarn add @cornerstonejs/codec-libjxl

Usage

The package exports separate JavaScript loaders and WASM binaries for decoding and encoding:

• @cornerstonejs/codec-libjxl/decodewasmjs
• @cornerstonejs/codec-libjxl/decodewasm
• @cornerstonejs/codec-libjxl/encodewasmjs
• @cornerstonejs/codec-libjxl/encodewasm

Decoder

import createJpegXLDecoder from '@cornerstonejs/codec-libjxl/decodewasmjs';

const codec = await createJpegXLDecoder();
const decoder = new codec.JpegXLDecoder();

decoder.getEncodedBuffer(bitstream.length).set(bitstream);
decoder.decode();

const frameInfo = decoder.getFrameInfo();
const decodedPixels = decoder.getDecodedBuffer();

Encoder

import createJpegXLEncoder from '@cornerstonejs/codec-libjxl/encodewasmjs';

const codec = await createJpegXLEncoder();
const encoder = new codec.JpegXLEncoder();
const frameInfo = {
  width,
  height,
  bitsPerSample,
  componentCount,
  isSigned: false,
};

encoder.getDecodedBuffer(frameInfo).set(decodedPixels);
encoder.setLossless(true);
encoder.encode();

const bitstream = encoder.getEncodedBuffer();

The encoder accepts greyscale samples with one channel or RGB samples with three channels at bit depths from 1 to 16. Copy returned buffer views before the next operation or before calling releaseBuffers().

setProgressive(true) writes a progressive stream: a decoder can show a preview from the first part of the stream. The encoder uses the same settings as cjxl -p (responsive mode and quantised progressive AC).

JPEG recompression

The DICOM transfer syntax JPEG XL JPEG Recompression (1.2.840.10008.1.2.4.111) stores a JPEG bitstream without loss. The encoder reads the JPEG bytes, not pixels, and the decoder gives back the same JPEG bytes:

encoder.getJpegBuffer(jpeg.length).set(jpeg);
encoder.encodeJpeg();
const jxl = encoder.getEncodedBuffer().slice();

decoder.getEncodedBuffer(jxl.length).set(jxl);
decoder.decodeToJpeg(); // throws if the stream has no JPEG reconstruction data
const sameJpeg = decoder.getJpegBuffer().slice();

Each encodeJpeg() consumes the JPEG buffer, so call getJpegBuffer() again before the next frame.

decode() also decodes such a stream to pixels.

Building

This project uses a Git submodule for libjxl. Initialize the submodules from the repository root:

git submodule update --init --recursive

An activated Emscripten SDK is required. Build both WASM modules with:

cd packages/libjxl
yarn build

The generated decoder and encoder .js and .wasm files are written to dist/.