JXL to FITS Converter
Processing entirely on your device — large files may take a moment.
JPEG XL Image and Flexible Image Transport System exist for different jobs: JPEG XL is a next-generation format designed to succeed JPEG: it can recompress existing JPG files about 60% smaller with no additional quality loss, and supports lossless mode and animation. Convert FITS frames to PNG or JPG to preview telescope data, or pack them into a ZIP for sharing.
Because the whole conversion happens on your device, it is instant, unlimited and genuinely private — no accounts, no watermarks, no files on anyone's server. Multiple files are converted in one go.
How JXL compares to FITS
| JXL | FITS | |
|---|---|---|
| Compression | Lossy and lossless | None (optionally Rice/GZIP) |
| Transparency | Supported | Not supported |
| Animation | Supported | Not supported |
| Metadata | EXIF, ICC carried over | Rich text header (WCS) |
| Best for | Archival and JPEG migration | Telescope frames, science data |
How to convert JXL to FITS
- 1
Select your files
Drag & drop your JXL files onto the area above, or click to browse. You can add multiple files at once for batch conversion.
- 2
Convert instantly
Click "Convert to FITS". The conversion runs entirely inside your browser using WebAssembly — no upload, no queue, no waiting.
- 3
Download results
Download each converted FITS file individually, or grab everything at once as a ZIP archive.
About the JXL format
JPEG XL (JXL, standardized 2021–2022) is the format designed to actually replace JPEG rather than merely coexist with it. Its headline trick: an existing JPG can be transcoded into JXL losslessly, shrinking it about 20% with zero further quality loss and the option to restore the original bytes later. Fresh encodes are smaller still — roughly 35–50% below JPG at equal quality — with animation, alpha and up to 32-bit float HDR support.
Adoption is the open question. Google pulled JXL from Chrome in 2023 (keeping an origin-trial path), Safari supports it since 17, and the encoder community remains enthusiastic. Today it is a superb archival and pipeline format — a way to future-proof JPEG libraries — while web deployment remains a calculated bet.
+Strengths
- ✓Lossless JPEG transcode (~20% smaller) with byte-exact restore
- ✓35–50% smaller than JPG on fresh encodes
- ✓Modern feature set: alpha, animation, HDR
!Limitations
- −Browser support is incomplete (Chrome pulled it)
- −Ecosystem and tooling are still young
- −Encoding slower than JPG
About the FITS format
FITS (Flexible Image Transport System) has carried professional astronomy data since 1981: every file opens with a plain-text header that records telescope, instrument, exposure, filters and world coordinates, followed by raw pixel arrays — often 16-bit or float, sometimes data cubes.
Values can be negative or far above display range, so FITS never looks right in a photo viewer. Converting to PNG applies a simple scaling pass that reveals the nebula or galaxy in the numbers — good for previews, while science pipelines keep the original.
+Strengths
- ✓Self-documenting science headers
- ✓High bit depth (16/32-bit, float)
- ✓The standard of every observatory
!Limitations
- −Not display-ready
- −Files are large and uncompressed
Why convert JXL to FITS?
Converting makes sense where the strengths of FITS meet what JXL cannot give you. Self-documenting science headers Meanwhile Browser support is incomplete (Chrome pulled it) One pass through the converter above puts your file on the right side of that trade-off.
Frequently asked questions
Is this JXL to FITS converter really free?
Yes — completely free, with no sign-up, no watermark and no daily conversion limits. The site is supported by advertising.
Are my files uploaded to a server?
No. The conversion runs entirely inside your browser using WebAssembly, so your files never leave your device — that is what makes it instant and private.
Does it work on Windows, Mac, iPhone and Android?
Yes. Anything with a modern browser works: Windows, macOS, Linux, Android and iOS. No software installation is required.
Will I lose quality converting JXL to FITS?
No — FITS is a lossless format, so every pixel of the converted image matches your original JXL file. You can also adjust the quality/size balance before converting when the target format supports compression.
What happens to EXIF data and other metadata?
Conversions here re-encode the image, and re-encoding generally does not carry the original metadata over. If the EXIF data of your JXL files matters (camera model, GPS, timestamps), keep the original file as the master and treat the converted copy as the shareable version.
Can I convert several JXL files at once?
Yes — drop as many files as you like into the tool and they are converted in one batch. When more than one file comes out, everything is bundled into a ZIP for a single download.