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Image MIME Reference
ACES

ACES Image Container File

image/aces
VS

T.38 Fax over IP (FoIP)

image/t38
T.38

A complete technical comparison of ACES Image Container File and T.38 Fax over IP (FoIP) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature ACES T.38
Transparency (Alpha) Yes ✕ No
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes ✕ No
EXIF Metadata ✕ No ✕ No
ICC Color Profile ✕ No ✕ No
ACES Image Container File
image/aces
Extension
.exr
Container OpenEXR (SMPTE ST 2065-4)
Compression Lossless / Uncompressed
Algorithm
PIZZIPRLEB44Uncompressed
Color Depth 16-bit (Half-float), 32-bit (Float)
Developed by Academy of Motion Picture Arts and Sciences (AMPAS) / SMPTE
Released 2013
Magic Bytes
76 2F 31 01
Full ACES reference →
T.38 Fax over IP (FoIP)
image/t38
Extension
.t38
Container UDPTL or TCP (Network Transport)
Compression Lossless (MH, MR, MMR / T.4, T.6)
Algorithm
MH (Modified Huffman)MR (Modified Read)MMR (Modified Modified Read)
Color Depth 1-bit (Monochrome B&W)
Developed by ITU-T (International Telecommunication Union)
Released 1998
Magic Bytes
None (Network Stream)
Full T.38 reference →

Browser Support Comparison

Browser ACES T.38
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
ACES

ACES Strengths

  • Industry standard for high-end visual effects, compositing, and color grading
  • Supports 16-bit half-float data, accurately capturing immense dynamic range without clipping
  • Standardized by SMPTE (ST 2065-4) to guarantee universal color interoperability across different post-production facilities
Limitations
  • Considerably larger file sizes than conventional consumer image formats
  • Completely unsupported in web browsers and most standard desktop viewers
  • Requires specialized compositing or color grading software to interpret and view the scene-linear data correctly
T.38

T.38 Strengths

  • Designed specifically to overcome the timing and packet-loss issues that plague traditional fax over standard VoIP audio codecs (like G.711)
  • Reduces bandwidth requirements by transmitting fax protocol data rather than uncompressed audio tones
  • Universally supported by enterprise SIP trunks and Session Border Controllers (SBCs) for FoIP
Limitations
  • Not an actual image file format, causing confusion due to its 'image/' MIME classification
  • Extremely complex to implement correctly over lossy UDP networks (relies on UDPTL redundancy mechanisms)
  • Zero support in web browsers or standard image viewing software

When to choose which format

ACES
Use ACES when…
  • Visual Effects (VFX)
  • Digital Intermediate (DI)
  • Color Grading
  • Archival
T.38
Use T.38 when…
  • Fax over IP (FoIP) Transmissions
  • SIP/SDP Media Negotiation
  • VoIP Gateways and PBX Systems
  • Enterprise Fax Servers

More comparisons

ACES vs APNG → T.38 vs APNG → ACES vs AVCI → T.38 vs AVCI → ACES vs AVCS → T.38 vs AVCS → ACES vs AVIF → T.38 vs AVIF → All comparisons →
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