zenjxl-decoder

A JPEG XL decoder in safe Rust. Fork of libjxl/jxl-rs with security hardening, bug fixes, and parallel decoding.

Maintained by Lilith River at Imazen.

[dependencies]
zenjxl-decoder = "0.3"

The Rust lib name is jxl, so you use jxl::... in code.

If you find a conformant JXL file that decodes incorrectly (or not at all), open an issue.

What's different from upstream

This fork fixes several decoding bugs, adds resource limits and cooperative cancellation, and wires up parallel decoding via rayon. All changes are BSD-3-Clause licensed under the Google CLA, intended for upstream contribution.

Bug Fixes

New Features

Usage

Basic decode

use jxl::api::{JxlDecoder, JxlDecoderOptions};

let data = std::fs::read("image.jxl")?;
let mut decoder = JxlDecoder::new(&data, JxlDecoderOptions::default());
// ... process frames

Resource limits

use jxl::api::{JxlDecoderLimits, JxlDecoderOptions};

// For untrusted input
let options = JxlDecoderOptions {
    limits: JxlDecoderLimits::restrictive(),
    ..Default::default()
};

All limits return Error::LimitExceeded { resource, actual, limit } when exceeded.

Cancellation

The decoder accepts any enough::Stop implementation:

use almost_enough::Stopper;
use std::sync::Arc;

let stop = Arc::new(Stopper::new());
let stop_clone = Arc::clone(&stop);

// Cancel from another thread
std::thread::spawn(move || {
    std::thread::sleep(std::time::Duration::from_secs(5));
    stop_clone.cancel();
});

let options = JxlDecoderOptions {
    stop,
    ..Default::default()
};

Cancellation checks run inside parallel closures too, so a cancel request is noticed mid-batch.

Parallel decoding

Enable the threads feature (on by default in jxl_cli):

[dependencies]
zenjxl-decoder = { version = "0.3", features = ["threads"] }

Set parallel: false on JxlDecoderOptions to force single-threaded mode at runtime.

Features

Conformance

Against libjxl/conformance test suite (Level 5): 17/23 passing (74%, as of December 2025).

cargo test --features cms conformance -- --ignored --nocapture

Against codec-corpus (184 JXL files with djxl reference output): 184/184 passing (100%, as of December 2025).

Upstream Contributions

Bug fixes reported to libjxl/jxl-rs:

Sister project

jxl-encoder — a multithreaded JPEG XL encoder in Rust, also by Imazen.

Image tech I maintain

* as of 2026

General Rust awesomeness

archmage · magetypes · enough · whereat · zenbench · cargo-copter

And other projects · GitHub @imazen · GitHub @lilith · lib.rs/~lilith · NuGet (over 30 million downloads / 87 packages)

License

BSD-3-Clause. See LICENSE.

Upstream Contribution

This is a fork of libjxl/jxl-rs (BSD-3-Clause). We are willing to release our improvements under the original BSD-3-Clause license if upstream takes over maintenance of those improvements. We'd rather contribute back than maintain a parallel codebase. Open an issue or reach out.