Image MIME Reference
JPEG-XR-(HEIF)
JPEG XR Image (HEIF Container)
image/jxra
VS
T.38 Fax over IP (FoIP)
image/t38
T.38
A complete technical comparison of JPEG XR Image (HEIF Container) 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 | JPEG-XR-(HEIF) | T.38 |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | Yes | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | Yes | ✕ No |
| ICC Color Profile | Yes | ✕ No |
JPEG XR Image (HEIF Container)
image/jxra
Extension
.jxra
Container
HEIF / ISOBMFF (ISO/IEC 23008-12 / Annex F of ITU-T T.832)
Compression
Lossy / Lossless
Algorithm
JPEG XR (Lapped Biorthogonal Transform)
Color Depth
8-bit, 16-bit, 32-bit (Float)
Developed by
ISO/IEC JTC 1 / ITU-T
Released
2019
Magic Bytes
XX XX XX XX 66 74 79 70 6A 78 72 41
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)
Browser Support Comparison
| Browser | JPEG-XR-(HEIF) | T.38 |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
JPEG-XR-(HEIF)
JPEG-XR-(HEIF) Strengths
- Combines the deep color (32-bit float) and mathematically lossless compression of JPEG XR with the robust metadata architecture of HEIF
- Allows grouping multiple images, exposure brackets, or focal stacks into a single file collection
Limitations
- Practically non-existent software and operating system support compared to standard HEIC or legacy JPEG XR (.jxr)
- Zero web browser support, rendering it entirely unsuitable for public web deployment
- Eclipsed by modern standards like AVIF and JPEG XL which offer superior compression with much broader industry backing
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
JPEG-XR-(HEIF)
Use JPEG-XR-(HEIF) when…
- Specialized Archival
- Experimental Imaging Workflows
- High Dynamic Range (HDR) Imaging
T.38
Use T.38 when…
- Fax over IP (FoIP) Transmissions
- SIP/SDP Media Negotiation
- VoIP Gateways and PBX Systems
- Enterprise Fax Servers