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Image MIME Reference
FITS

Flexible Image Transport System

image/fits
VS

Extended Image File Format

image/vnd.xiff
XIFF

A complete technical comparison of Flexible Image Transport System and Extended Image File Format — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature FITS XIFF
Transparency (Alpha) ✕ No ✕ No
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes ✕ No
EXIF Metadata ✕ No ✕ No
ICC Color Profile ✕ No ✕ No
Flexible Image Transport System
image/fits
Extension
.fits.fit.fts
Container FITS
Compression Uncompressed / Tile Compressed (Rice, GZIP)
Algorithm
UncompressedRiceGZIPHcompress
Color Depth 8-bit, 16-bit, 32-bit, 64-bit (Float/Double)
Developed by IAU FITS Working Group / NASA
Released 1981
Magic Bytes
53 49 4D 50 4C 45 20 20 3D 20
Full FITS reference →
Extended Image File Format
image/vnd.xiff
Extension
.xif
Container TIFF-based Proprietary Container
Compression CCITT Group 3 / Group 4 / LZW / Uncompressed
Algorithm
CCITT Group 4LZWNone
Color Depth 1-bit (Monochrome), 8-bit (Grayscale), 24-bit (RGB)
Developed by Keyfile Corporation
Released 1994
Magic Bytes
49 49 2A 00 or 4D 4D 00 2A
Full XIFF reference →

Browser Support Comparison

Browser FITS XIFF
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
FITS

FITS Strengths

  • The undisputed global standard for archiving and sharing astronomical data
  • Self-documenting: Headers are written in plain ASCII, ensuring data is readable decades later regardless of software
  • Supports incredibly high dynamic range, N-dimensional arrays, and complex binary tables
Limitations
  • No support in standard consumer software or web browsers
  • Uncompressed raw FITS files from modern telescopes can be excessively large
  • Does not use standard metadata models like EXIF or XMP, requiring specialized parsers
XIFF

XIFF Strengths

  • Pioneered early enterprise document workflow integration by binding administrative routing data directly to the document image file
  • Leveraged efficient fax compression standards to keep storage requirements low on 1990s server infrastructure
Limitations
  • Completely proprietary and obsolete; Keyfile Corporation's software ecosystem no longer exists
  • Causes widespread MIME type identification conflicts due to sharing the exact same binary header signature as standard TIFF files
  • Zero support in modern operating systems or web browsers

When to choose which format

FITS
Use FITS when…
  • Astronomy & Astrophysics
  • Space Telescope Data (Hubble, JWST)
  • Scientific Data Archiving
  • Spectroscopy
XIFF
Use XIFF when…
  • Keyfile Enterprise Document Management
  • Legacy Corporate Workflow Archival
  • Scanned Multi-page Document Routing

More comparisons

FITS vs ACES → XIFF vs ACES → FITS vs APNG → XIFF vs APNG → FITS vs AVCI → XIFF vs AVCI → FITS vs AVCS → XIFF vs AVCS → FITS vs AVIF → XIFF vs AVIF → All comparisons →
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