Image MIME Reference
FLIF
Free Lossless Image Format
image/flif
VS
T.38 Fax over IP (FoIP)
image/t38
T.38
A complete technical comparison of Free Lossless Image Format 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 | FLIF | T.38 |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | Yes | ✕ No |
| Progressive Loading | Yes | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | Yes | ✕ No |
| ICC Color Profile | Yes | ✕ No |
Free Lossless Image Format
image/flif
Extension
.flif
Container
FLIF Bitstream
Compression
Lossless (MANIAC Entropy Coding)
Algorithm
MANIAC (Meta-Adaptive Near-zero Integer Arithmetic Coding)
Color Depth
1-bit to 16-bit (Per Channel), Grayscale, RGB, RGBA, CMYK
Developed by
Jon Sneyers and Pieter Wuille (Cloudinary)
Released
2015
Magic Bytes
46 4C 49 46
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 | FLIF | T.38 |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
FLIF
FLIF Strengths
- Achieves some of the highest lossless compression ratios ever developed for raster images
- Incredible progressive decoding allows an image to be highly recognizable even after only 5% of the file has been downloaded
- Supports animations and complex alpha channels losslessly
Limitations
- Officially abandoned in favor of JPEG XL
- Zero native support in web browsers or standard operating system previewers
- Encoding speed can be significantly slower than standard PNG or WebP compression
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
FLIF
Use FLIF when…
- Archival of Uncompressed Image Assets
- Bandwidth-Constrained Progressive Image Loading (Historical)
- Medical and Scientific Imaging Storage
T.38
Use T.38 when…
- Fax over IP (FoIP) Transmissions
- SIP/SDP Media Negotiation
- VoIP Gateways and PBX Systems
- Enterprise Fax Servers