What Is a .JXL File?

JPEG XL Image (.jxl)

Overview

JPEG XL is a royalty-free image format standardised in 2022 by the JPEG committee as the intended successor to JPEG. It covers lossy and lossless compression in one codec, decodes progressively, supports HDR, animation, transparency and very large images, and has one feature no other modern format offers: it can recompress an existing JPEG file losslessly, about 20 percent smaller, and restore the original bit for bit.

Technically it is the most capable of the post-JPEG formats. Its adoption has been the drama: Chrome shipped it behind a flag, removed it in 2023, and then the ecosystem split, with Apple adding support across its platforms in 2023 and Firefox and Chromium reconsidering since.

Technical Specifications

• MIME Type: image/jxl
• File Extension: .jxl
• Category: Image
• Standard: ISO/IEC 18181 (parts 1 to 4, 2022)
• Modes: VarDCT (lossy, JPEG-like transform coding) and Modular (lossless and near-lossless)
• Bit depth: up to 32 bits per channel, float
• Colour: any ICC profile, HDR (PQ, HLG), wide gamut, CMYK, up to 4099 channels
• Max size: over a billion pixels per side
• Reference implementation: libjxl
• Magic bytes: FF 0A (bare codestream) or 00 00 00 0C 4A 58 4C 20 0D 0A 87 0A (container)

Identification

Two forms exist:

Bare codestream:   ff 0a ...
Container:         00 00 00 0c 4a 58 4c 20 0d 0a 87 0a   |....JXL ....|

The container form wraps the codestream in boxes (the JXL signature box, then ftyp with brand jxl ) so it can carry metadata such as Exif and XMP. The 0D 0A 87 0A tail is the same trick PNG uses to catch text-mode corruption.

History and Development

The JPEG committee called for proposals in 2017 and merged two: Google's PIK and Cloudinary's FUIF. The result reached ISO standardisation in 2022. Its design goals were explicit: beat JPEG by a wide margin, support everything photographers and the web need, and provide a lossless migration path for the trillions of existing JPEGs.

Chrome had JPEG XL behind a flag from version 91 and removed it in version 110 (early 2023), citing insufficient interest. That decision drew an unusual volume of public objection from Adobe, Facebook, Intel, Shopify and others. Apple then shipped support in Safari 17, macOS Sonoma and iOS 17 (2023), and in Camera for the iPhone 16 Pro's ProRAW. Mozilla moved from "neutral" to implementing in 2024, and Chromium discussions reopened. As of 2026 the format is native on Apple platforms and in a growing set of applications, with browser support still uneven.

Common Use Cases

• Photo archiving: losslessly recompressing JPEG libraries to recover roughly a fifth of the space, reversibly
• HDR and wide-gamut photography on Apple devices
• Professional imaging: high bit depth, CMYK, many channels, huge dimensions
• Lossless graphics where it beats PNG and WebP on size
• Web delivery to Safari, with AVIF or JPEG fallback for other browsers

How to Open a JXL File

macOS, iOS and iPadOS

• Native since macOS 14 Sonoma and iOS 17: Preview, Photos, Quick Look, Safari and any app using the system image frameworks.

Windows

• No built-in support. Install the free JPEG XL Image Extension (jxl-winthumb or the Microsoft Store listing by the libjxl community) for Explorer thumbnails and Photos.
• IrfanView and XnView MP open JXL with their plugins. Paint.NET has a JXL plugin. GIMP 2.10.32+ and Krita 5.1+ support it natively.

Linux

• GIMP, Krita, Darktable 4.2+; GTK viewers via the jxl-pixbuf-loader package; KDE via kimageformats.

Browsers

• Safari 17+: yes.
• Firefox: behind image.jxl.enabled in Nightly; shipping status has been changing.
• Chrome and Edge: not without an extension, as of 2026. Check caniuse for the current state before relying on it.

Android

• Not system-wide as of Android 15; Samsung Gallery and some third-party viewers decode it.

How to Convert a JXL File

JPEG to JXL, losslessly (the headline feature)

# Recompress an existing JPEG with no quality loss; reversible
cjxl photo.jpg photo.jxl

# Get the original JPEG back, byte for byte
djxl photo.jxl photo.jpg

cjxl detects JPEG input and uses the lossless-transcode mode by default. Expect 15 to 25 percent smaller files.

PNG or other sources to JXL

# Lossy, quality 90 (distance 1.0 is visually lossless for most content)
cjxl photo.png -q 90 photo.jxl

# Lossless
cjxl graphic.png -d 0 graphic.jxl

# Effort: 1 (fast) to 9 (slow, smallest); 7 is the default
cjxl photo.png -d 1 -e 8 photo.jxl

JXL to common formats

djxl photo.jxl photo.png
magick photo.jxl -quality 92 photo.jpg     # ImageMagick 7 with libjxl

Other tools

• ImageMagick 7, GraphicsMagick, libvips and sharp (Node) all read and write JXL when built with libjxl.
• Squoosh offers JXL encoding in the browser.
• XnConvert for graphical batch conversion.

Advantages

• Best-in-class compression across lossy and lossless in one codec.
• Lossless JPEG recompression, unique among modern formats.
• Progressive decoding: a usable preview from the first few percent of the file.
• No practical limits on size, bit depth, channels or colour space.
• Royalty-free with a BSD-licensed reference implementation.
• Fast decoding, roughly on par with JPEG and far ahead of AVIF.

Limitations

• Browser support is the problem: without Chrome, it cannot be the only format served on the web.
• Tooling is younger than AVIF's in CDNs and frameworks.
• Windows needs an extension for even basic viewing.
• Uncertain trajectory: adoption depends on decisions outside the format's control.

Related Formats

• JPEG: what JXL succeeds and can losslessly repackage.
• AVIF: the competing modern format with universal browser support.
• HEIF: Apple's camera format, which JXL is beginning to share platform support with.
• PNG: the lossless format JXL outperforms on size.