Image MIME Reference
Canon-CR2
Canon Raw Version 2
image/x-canon-cr2
VS
T.38 Fax over IP (FoIP)
image/t38
T.38
A complete technical comparison of Canon Raw Version 2 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 | Canon-CR2 | T.38 |
|---|---|---|
| Transparency (Alpha) | ✕ No | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | Yes | ✕ No |
| ICC Color Profile | Yes | ✕ No |
Canon Raw Version 2
image/x-canon-cr2
Extension
.cr2
Container
TIFF
Compression
Lossless JPEG (ITU-T81)
Algorithm
Lossless JPEG (ITU-T81)
Color Depth
12-bit (Per Channel), 14-bit (Per Channel)
Developed by
Canon Inc.
Released
2004
Magic Bytes
49 49 2A 00 10 00 00 00 43 52 02 00
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 | Canon-CR2 | T.38 |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
Canon-CR2
Canon-CR2 Strengths
- Retains maximum sensor data, allowing extreme recovery of highlights and shadows that would be permanently lost in a JPEG
- White balance and color profiling are not 'baked in', meaning they can be completely altered in post-production without degrading the image
- Lossless compression ensures perfect pixel accuracy while reducing file size compared to fully uncompressed formats
Limitations
- Proprietary format means it requires constant updates to raw processing engines (like Adobe Camera Raw) every time Canon releases a new camera model
- Produces very large file sizes (often 20MB to 40MB per image depending on sensor resolution)
- Cannot be directly embedded into web pages or used in standard HTML/CSS contexts
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
Canon-CR2
Use Canon-CR2 when…
- Professional Digital Photography
- Non-destructive Image Post-Processing
- High Dynamic Range (HDR) Imaging Archival
T.38
Use T.38 when…
- Fax over IP (FoIP) Transmissions
- SIP/SDP Media Negotiation
- VoIP Gateways and PBX Systems
- Enterprise Fax Servers