Image MIME Reference
DNG
Adobe Digital Negative
image/x-adobe-dng
VS
Group 3 Fax Image
image/g3fax
G3-Fax
A complete technical comparison of Adobe Digital Negative and Group 3 Fax Image — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | DNG | G3-Fax |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | Yes | ✕ No |
| ICC Color Profile | Yes | ✕ No |
Adobe Digital Negative
image/x-adobe-dng
Extension
.dng
Container
TIFF/EP
Compression
Lossless JPEG / Deflate / Lossy JPEG (DNG 1.4+)
Algorithm
Lossless JPEG (Standard)Lossy JPEG (Compression option)Uncompressed
Color Depth
12-bit, 14-bit, 16-bit, 32-bit (Floating Point HDR)
Developed by
Adobe Systems
Released
2004
Magic Bytes
49 49 2A 00 or 4D 4D 00 2A
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)
Browser Support Comparison
| Browser | DNG | G3-Fax |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
DNG
DNG Strengths
- Openly documented specification guarantees long-term archival accessibility, freeing photographers from proprietary manufacturer lock-in
- Lossless compression algorithms often result in files 15-20% smaller than uncompressed proprietary raw formats
- Natively supported by modern smartphone operating systems (iOS and Android) for high-end mobile photography
Limitations
- Conversion from proprietary raw to DNG takes processing time and can strip specific, proprietary manufacturer metadata (like active D-Lighting or in-camera lens corrections)
- File sizes are massive compared to standard JPEGs or HEIC files
- Cannot be rendered natively in web browsers without server-side processing or WebAssembly decoders
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
When to choose which format
DNG
Use DNG when…
- Digital Photography Archival
- Mobile Raw Capture (iOS ProRAW / Android Camera2 API)
- Cross-Platform Raw Editing Workflows
G3-Fax
Use G3-Fax when…
- Telefacsimile (Fax) Transmission
- Internet Fax (T.37)
- Document Archiving
- Telephony Systems