Image MIME Reference
CGM
Computer Graphics Metafile
image/cgm
VS
Group 3 Fax Image
image/g3fax
G3-Fax
A complete technical comparison of Computer Graphics Metafile 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 | CGM | G3-Fax |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | ✕ No | ✕ No |
| ICC Color Profile | Yes | ✕ No |
Computer Graphics Metafile
image/cgm
Extension
.cgm
Container
CGM
Compression
Uncompressed / Binary / Character / Clear Text
Algorithm
Deflate (in some WebCGM profiles)
Color Depth
8-bit, 16-bit, 24-bit, 32-bit
Developed by
ISO / IEC
Released
1987
Magic Bytes
00 20 (Binary) / 42 45 47 49 4E 20 4D 45 54 41 46 49 4C 45 (Clear Text)
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 | CGM | G3-Fax |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
CGM
CGM Strengths
- Strictly standardized by ISO, ensuring long-term archiving and cross-platform compatibility in engineering
- Excellent support for rich metadata, hyperlinks, and technical hotspots via the WebCGM profile
- Can store complex 2D geometry, rasters, and text in a single lightweight file
Limitations
- Multiple encoding schemes (Binary, Character, Clear Text) make parser development difficult
- Zero native support in modern web browsers without third-party plugins
- Largely replaced by SVG for general-purpose 2D vector graphics on the web
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
CGM
Use CGM when…
- Technical Illustrations
- Aerospace & Defense (S1000D)
- CAD/CAM
- Geophysics
G3-Fax
Use G3-Fax when…
- Telefacsimile (Fax) Transmission
- Internet Fax (T.37)
- Document Archiving
- Telephony Systems