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File Format Guide
What is a JXL file?
JPEG XL is technically the most complete image format anyone has shipped — excellent lossy compression, genuinely good lossless compression, and a migration path that shrinks existing JPEGs without touching their quality. Its problem has never been the technology.
JXL at a glance
What is a JXL file?
The newest evolution of the JPEG format. It is designed to replace legacy JPEG, GIF, and PNG with a single, highly efficient format that supports both lossy and lossless compression, animations, and progressive loading.
How to open a JXL file?
Support is currently growing. Apple devices support it natively (iOS 17/macOS Sonoma). Web browser support is still experimental or requires flags to be enabled in Chrome/Firefox.
Typical use of a JXL file:
Future web deployment and high-quality photo archiving. It has the unique ability to re-compress legacy JPGs into smaller JXL files without losing any quality.
Origin of the JXL file:
Standardized by the Joint Photographic Experts Group in 2021.
Modern alternatives for JXL:
AVIF and WebP are its main competitors, currently boasting much wider browser support than JXL.
JXL specifications
Full name
JPEG XL
File extensions
.jxl
MIME type
image/jxl
Compression
Lossy and lossless, both strong; plus lossless JPEG recompression
Transparency
Full alpha channel
Animation
Supported
Colour depth
Up to 32-bit float per channel, with HDR and wide gamut
Standardised
ISO/IEC 18181, 2021–2022
Licensing
Royalty-free
Browser support
Safari 17+; not enabled by default in Chrome or Firefox
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The trick nothing else can do
JPEG XL can take an existing JPEG and re-encode it losslessly, producing a file around 20% smaller from which the original JPEG — byte for byte identical — can be reconstructed on demand. No quality is lost, because nothing is re-compressed; the format simply stores the same coefficients more efficiently.
For anyone sitting on a large JPEG archive this is a genuinely unusual proposition. Every other modernisation path asks you to re-encode lossy data and accept some further degradation, or to accept that you can never get the original back. JXL asks for neither.
How it compares to AVIF and WebP
For lossy photographic compression JXL and AVIF are broadly comparable, with JXL tending to hold up better at high quality settings and AVIF tending to win at very low bitrates. For lossless compression JXL is clearly ahead of both, typically beating PNG by a wide margin. JXL also encodes considerably faster than AVIF, which matters for anything generated on demand.
It supports progressive decoding as well — a partially downloaded file renders as a complete but lower-detail image rather than as a half-drawn one. AVIF cannot do this, and on slow connections it is a real perceptual difference.
The support problem
Chrome shipped JXL behind a flag and then removed it in 2023, citing insufficient ecosystem interest and the maintenance burden of the decoder. Safari added support in version 17. Firefox has an implementation available in pre-release builds but not enabled by default. Support outside browsers — in operating systems, editors, and phone galleries — has grown steadily but remains partial.
The practical upshot: JXL is an excellent archival and working format and a risky delivery format. Serving JXL to the open web today means most visitors cannot see the image without a fallback.
Converting JXL files
If you have been handed a .jxl and your software will not open it, converting to JPG or PNG is the fix — PNG if the image has transparency or you intend to edit it, JPG if you simply need something universally readable.
Going the other way, converting a lossless master to JXL is worthwhile for storage. Converting an existing JPEG to JXL is worthwhile too, but only using the lossless recompression path; a plain lossy re-encode throws away quality for no good reason.
Convert JXL files in your browser
Zolvo's image converter runs entirely on your own machine — your files are never uploaded to a
server. Drop a JXL file in and pick an output format, or jump straight to a common one:
It depends on the job. JXL is better at lossless compression, encodes much faster, decodes progressively, and can losslessly recompress existing JPEGs. AVIF compresses better at very low bitrates and has far broader browser support. For delivery today, AVIF is the safer choice.
Why won't Chrome open JXL files?
Chrome shipped JPEG XL behind a flag and removed the code in 2023, citing limited ecosystem adoption. Safari 17 and later support it. Until that changes, converting to JPG or PNG is the reliable way to view a JXL on most systems.
Can JPEG XL really shrink JPEGs without quality loss?
Yes — this is its most distinctive feature. It re-encodes the existing JPEG data more efficiently, typically saving around 20%, and the original JPEG can be reconstructed byte for byte. No re-compression takes place, so no quality is lost.
Should I archive my photos as JXL?
It is a defensible choice: lossless JXL is smaller than PNG or TIFF, and the format is a published ISO standard so it will remain readable. The counter-argument is tooling — if your backup, catalogue, and viewing software do not all support it, the space saving may not be worth the friction.
