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Image MIME Reference
AZV

AirZip Accelerator Image

image/vnd.airzip.accelerator.azv
VS

Flexible Image Transport System

image/fits
FITS

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

Equal browser support

Feature Support

Feature AZV FITS
Transparency (Alpha) ✕ No ✕ No
Animation Support ✕ No ✕ No
Progressive Loading Yes ✕ No
HDR Support ✕ No Yes
EXIF Metadata ✕ No ✕ No
ICC Color Profile ✕ No ✕ No
AirZip Accelerator Image
image/vnd.airzip.accelerator.azv
Extension
.azv
Container Proprietary AirZip Container
Compression Lossy (Proprietary) / Lossless (Proprietary)
Algorithm
AirZip Proprietary Compression
Color Depth 8-bit (Indexed), 24-bit (RGB)
Developed by AirZip, Inc.
Released 1999
Magic Bytes
Unknown (Proprietary)
Full AZV reference →
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 →

Browser Support Comparison

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

AZV Strengths

  • Historically allowed internet users to browse the web up to 5x faster over 56k dial-up modems by drastically reducing image payload sizes
  • Officially registered in the IANA vendor tree, preventing MIME type conflicts on early web proxy servers
Limitations
  • Completely obsolete in the modern broadband era
  • Closed-source and proprietary, meaning no modern image manipulation libraries (like ImageMagick or libvips) can decode it
  • Zero support in standard web browsers
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

When to choose which format

AZV
Use AZV when…
  • Dial-up Web Acceleration
  • Bandwidth Optimization (Historical)
  • Legacy Proxy Servers
FITS
Use FITS when…
  • Astronomy & Astrophysics
  • Space Telescope Data (Hubble, JWST)
  • Scientific Data Archiving
  • Spectroscopy

More comparisons

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