Cookies for analytics and advertising
We use cookies for analytics and advertising, both sent to Google. Refusing changes nothing you can see.Read the privacy page
JXL
What is a JXL file?
The JPEG successor. Can repack existing JPGs 20% smaller without touching image quality.
What JXL is
JXL is a binary format, meaningful only to a program that knows it. It stores a grid of pixels, so enlarging it past its own resolution softens it. It is used for archiving and photography.
The extension is .jxl, and the full name is JPEG XL. Both matter less than what the file can hold, which is what the rest of this page is about.
Where JXL came from
Joint Photographic Experts Group published it in 2021. The specification is ISO/IEC 18181.
Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.
The specification is public
Anyone can implement it without asking permission or paying a licence, which is why it turns up in so many programs and why files written twenty years ago still open.
It is a specialist format
It exists to do one job well for one group of people. Outside that job it is a poor default, and inside it there is usually nothing better.
Nothing is thrown away
JXL stores its content exactly. Saving it again changes nothing, so it can be opened, edited and re-saved as often as you like without accumulating damage — which is what makes it a working format rather than a delivery one.
It can be transparent
JXL carries an alpha channel, so a logo keeps its soft edges over whatever sits behind it instead of arriving in a white box.
It can hold more than one frame
JXL can store an animation rather than a single still. That is worth knowing before converting one: a target that holds one frame keeps the first and drops the rest, usually without saying so.
Colour it can describe
Up to 32 bits per channel. It can work in RGB, greyscale and wide-gamut colour.
More than eight bits per channel is what stops a gradient from stepping when it is edited, which is why it matters in a working file and rarely in a finished one.
What opens JXL
GIMP and ImageMagick read it, and so do most programs of the same kind.
If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.
Opening it in a browser
Only some browsers read it.
Where support is uneven, serving a second format alongside it is the usual answer — the browser takes the one it understands and nobody is left out.
What it can carry besides the content
JXL can hold EXIF, XMP and ICC profiles.
Whether any of it survives a conversion depends entirely on the target, and the honest answer is usually "some of it".
It is a delivery format
JXL is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.
What goes wrong with it
The recurring complaints: support outside its home ground is uneven.
None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.
The facts, in one place
| Extension | .jxl |
|---|---|
| Media type | image/jxl |
| Published by | Joint Photographic Experts Group |
| First published | 2021 |
| Specification | ISO/IEC 18181 |