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Image MIME Reference
FITS

Flexible Image Transport System

image/fits
VS

Portable Network Graphics (Legacy MIME)

image/x-png
PNG

A complete technical comparison of Flexible Image Transport System and Portable Network Graphics (Legacy MIME) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

PNG wins on browser support

Feature Support

Feature FITS PNG
Transparency (Alpha) ✕ No Yes
Animation Support ✕ No ✕ No
Progressive Loading ✕ No Yes
HDR Support Yes Yes
EXIF Metadata ✕ No Yes
ICC Color Profile ✕ No Yes
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 →
Portable Network Graphics (Legacy MIME)
image/x-png
Extension
.png
Container PNG Chunk Structure (IHDR, IDAT, IEND)
Compression Deflate (Lossless)
Algorithm
Deflate (LZ77)
Color Depth 1-bit to 16-bit (Grayscale), 8-bit (Indexed Palette), 24-bit (True Color), 32-bit (True Color with Alpha), 48-bit (High Color), 64-bit (High Color with Alpha)
Developed by PNG Development Group
Released 1996
Magic Bytes
89 50 4E 47 0D 0A 1A 0A
Full PNG reference →

Browser Support Comparison

Browser FITS PNG
Chrome Chrome
✕
✓ 1
Firefox Firefox
✕
✓ 1
Safari Safari
✕
✓ 1
Edge Edge
✕
✓ 12
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
PNG

PNG Strengths

  • The underlying format provides flawless, lossless compression and perfect 8-bit alpha channel transparency
  • Universally supported by every modern operating system, image editor, and web browser
Limitations
  • The 'image/x-png' string is an obsolete vendor quirk that forces backend developers to write redundant normalization logic in file upload scripts
  • If left unnormalized, strict MIME validators or content security policies on modern systems may incorrectly reject valid PNG files

When to choose which format

FITS
Use FITS when…
  • Astronomy & Astrophysics
  • Space Telescope Data (Hubble, JWST)
  • Scientific Data Archiving
  • Spectroscopy
PNG
Use PNG when…
  • Legacy Internet Explorer File Uploads
  • Older ASP/PHP Web Applications
  • Lossless Web Graphics

More comparisons

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