Image MIME Reference
G3-Fax
Group 3 Fax Image
image/g3fax
VS
High Efficiency Image Container
image/heic
HEIC
A complete technical comparison of Group 3 Fax Image and High Efficiency Image Container — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
HEIC wins on browser support
Feature Support
| Feature | G3-Fax | HEIC |
|---|---|---|
| Transparency (Alpha) | ✕ No | Yes |
| Animation Support | ✕ No | Yes |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | Yes |
| EXIF Metadata | ✕ No | Yes |
| ICC Color Profile | ✕ No | Yes |
Group 3 Fax Image
image/g3fax
Extension
.g3
Container
Raw Bitstream
Compression
Lossless (CCITT Group 3)
Algorithm
CCITT Group 3 (Modified Huffman / READ)
Color Depth
1-bit (Monochrome)
Developed by
CCITT (now ITU-T) / IETF
Released
1980
Magic Bytes
None (Raw Bitstream)
High Efficiency Image Container
image/heic
Extension
.heic
Container
HEIF / ISOBMFF
Compression
Lossy / Lossless
Algorithm
HEVC (H.265)
Color Depth
8-bit, 10-bit, 12-bit, 16-bit
Developed by
MPEG (Standard) / Apple (Adoption)
Released
2017
Magic Bytes
XX XX XX XX 66 74 79 70 68 65 69 63
Browser Support Comparison
| Browser | G3-Fax | HEIC |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ |
✓ 11+
|
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
G3-Fax
G3-Fax Strengths
- Extremely efficient compression for 1-bit black-and-white text and line art
- Standardized via RFC 1494 for email and internet fax transmission
- Low bandwidth requirements
Limitations
- Raw format lacks metadata (such as image width and resolution), requiring out-of-band information to decode accurately
- Strictly limited to 1-bit monochrome imagery
- Zero native web browser support
HEIC
HEIC Strengths
- Exceptional compression efficiency — stores images at roughly half the file size of JPEG with equal or better visual quality
- Natively supports modern photography features like depth maps, 16-bit color, HDR, and alpha channel transparency
- Can store image bursts, focal stacks, and animations (Live Photos) within a single file
Limitations
- Heavily encumbered by software patents, leading to very poor adoption outside the Apple ecosystem
- Not supported by standard web browsers (except Safari), requiring server-side or client-side conversion for web delivery
- Windows requires downloading a separate (often paid) extension from the Microsoft Store to view natively
When to choose which format
G3-Fax
Use G3-Fax when…
- Telefacsimile (Fax) Transmission
- Internet Fax (T.37)
- Document Archiving
- Telephony Systems
HEIC
Use HEIC when…
- iOS / iPhone Photography
- macOS Ecosystem
- High-Quality Image Archiving