FITS to GZ Converter
Processing entirely on your device — large files may take a moment.
Flexible Image Transport System and Gzip Compressed File exist for different jobs: FITS (Flexible Image Transport System) is the data format of professional astronomy — every image carries a human-readable header with telescope, exposure and world coordinates alongside the raw pixel data. Unpack a .gz into a normal file or repack it as ZIP/TAR when the receiving tool does not understand gzip.
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 FITS compares to GZ
| FITS | GZ | |
|---|---|---|
| Compression | None (optionally Rice/GZIP) | DEFLATE |
| Best for | Telescope frames, science data | Logs, dumps, datasets |
How to convert FITS to GZ
- 1
Select your files
Select your FITS file.
- 2
Convert instantly
The file bytes are gzip-compressed in place — the same archive your server or build tool produces, made locally.
- 3
Download results
Download the .gz file — ready to upload, serve or attach.
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
About the GZ format
A .gz file is one file squeezed by gzip — not an archive. kernel.org tarballs are “tar inside gz”, but plenty of logs, JSON dumps and CSV exports travel as plain .gz. Opening one means decompressing it back to the original bytes.
Repacking into ZIP or TAR gives the decompressed file a container that every GUI tool opens without a second thought.
+Strengths
- ✓Everywhere on Linux and macOS
- ✓Fast, well-understood compression
- ✓Streams natively from any tool
!Limitations
- −Single file only — no directory tree
- −No encryption or integrity metadata
Why convert FITS to GZ?
There is a concrete reason this conversion exists: Not display-ready GZ sidesteps that — Everywhere on Linux and macOS If that is your situation, the tool above settles it in seconds, entirely on your device.
Frequently asked questions
Is this FITS to GZ 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 FITS to GZ?
No — GZ is a lossless format, so every pixel of the converted image matches your original FITS file. You can also adjust the quality/size balance before converting when the target format supports compression.
Are the files inside my FITS archive modified?
No. Contents are unpacked in memory and repacked into GZ byte-for-byte — the conversion changes the container, never the files inside it.
What about folders and directory structure?
The full directory tree is preserved: folders stay folders, and deep paths arrive exactly as they were packed in the FITS file.