October 16, 2026 · 6 min read

What Is JPEG XL (JXL)? The Image Format Built to Replace JPG and PNG

JPEG XL, usually written JXL, is a royalty-free image format standardised as ISO/IEC 18181 and developed by the Joint Photographic Experts Group - the same committee behind the original JPEG. It was designed from the start to be a single format that can replace JPG, PNG and GIF, while beating all of them on file size and quality.

What is JPEG XL?

JXL is a general-purpose raster image format. It handles photographs, screenshots, illustrations, transparency, animation and high dynamic range in one codec, and it does so with both lossy and lossless compression. Its design came out of two earlier research projects, Google's PIK and Cloudinary's FUIF, which were merged into the final standard.

The goal was practical rather than academic: take the best ideas in modern image compression and make them fast enough to decode on a phone, flexible enough for professional workflows, and free of patent licensing worries.

Why JPEG XL is so good

• Smaller files. At the same visual quality, JXL photos are typically 30-60% smaller than JPG, and lossless JXL is commonly 35-50% smaller than PNG.
• Lossless JPEG recompression. An existing JPG can be converted to JXL about 20% smaller and then converted back to the byte-identical original. Nothing is lost, and no other modern format offers this.
• One format for everything. Lossy photos, lossless graphics, alpha transparency, animation and multiple layers all live in the same codec.
• HDR and wide colour. JXL supports up to 32 bits per channel, wide-gamut colour spaces and HDR transfer functions, which JPG cannot do at all.
• Progressive decoding. A JXL image can show a usable preview from the first small fraction of the file and sharpen as the rest arrives, which helps on slow connections.
• Fast encoding and decoding. Compared with AVIF, JXL encodes much faster and scales well across CPU cores, which matters for large image libraries.
• Huge images. JXL supports images of up to roughly a billion pixels on a side, far beyond the 65,535-pixel limit of JPG.
• Better generation loss. Re-saving a JXL image repeatedly degrades far less than doing the same with JPG.

JXL vs JPG, PNG, WebP and AVIF

JPG is universally supported but dates from 1992, has no transparency and shows blocky artefacts at high compression. PNG is lossless and supports transparency but produces large files for photos. WebP improved on both, and AVIF pushed compression further, especially at very low bitrates.

JXL's edge is that it is strong everywhere. AVIF can look smoother at extreme compression, but JXL tends to keep fine texture and detail at high quality, encodes far faster, supports larger images and offers the lossless JPEG transcode that none of the others do. If you care about quality, archival value and speed rather than the absolute smallest thumbnail, JXL is hard to beat.

Browser and software support

Support is the honest weak spot. Safari has supported JPEG XL natively since version 17, and a growing list of tools - including Photoshop, GIMP, Affinity, ImageMagick, libvips and many Linux and Android galleries - can read and write it. Chromium and Firefox have moved back and forth on shipping a decoder, so support across browsers is still not universal.

That means JXL is an excellent choice today for archives, photography workflows, asset pipelines and Apple-centric audiences, and a progressive-enhancement choice for the public web, where you would serve it through a <picture> element with AVIF, WebP or JPG fallbacks.

When should you use JXL?

• Archiving a photo library, where lossless JPEG recompression saves space with zero risk.
• Storing high-quality masters, HDR images or very large scans and panoramas.
• Delivering images to environments you control that already support the format.
• Cutting storage and bandwidth costs for image-heavy workflows.

Convert to and from JXL in your browser

You do not need to install anything to try the format. Rebytify converts JXL files to PNG, JPG, WebP or AVIF, and turns your existing images into JXL, all inside your browser using WebAssembly. Your files are never uploaded. One note: Rebytify decodes your image to pixels and writes a new JXL file. It does not perform the bit-exact, reversible JPEG transcode, which is a feature of the cjxl command line tool.