Image MIME Reference
PICT
Apple PICT Image
image/x-pict
VS
T.38 Fax over IP (FoIP)
image/t38
T.38
A complete technical comparison of Apple PICT Image 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 | PICT | T.38 |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | ✕ No | ✕ No |
| ICC Color Profile | ✕ No | ✕ No |
Apple PICT Image
image/x-pict
Extension
.pict.pct.pic
Container
QuickDraw Metafile
Compression
Uncompressed / Run-Length Encoding (RLE) / QuickTime Compressors (JPEG, SMC)
Algorithm
Apple PackBits (RLE)QuickTime Image Compression Manager (ICM)
Color Depth
1-bit, 2-bit, 4-bit, 8-bit (Indexed), 16-bit (High Color), 24-bit (True Color), 32-bit (RGBA)
Developed by
Apple Computer, Inc.
Released
1984
Magic Bytes
None (Requires offset parsing, e.g., 00 11 02 FF at byte 522)
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 | PICT | T.38 |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
PICT
PICT Strengths
- Incredibly versatile for its time, allowing a single file to cleanly scale text and vector shapes while simultaneously housing raster photos
- Served as the flawless universal clipboard format for the classic Mac OS, enabling seamless copy/pasting between wildly different applications
Limitations
- Deeply tied to Apple's legacy QuickDraw graphics architecture, making it exceptionally difficult to write accurate third-party parsers on modern operating systems
- Lack of a standard magic header makes file detection unreliable without seeking 522 bytes deep into the file
- Completely unsupported in modern web environments and discontinued by Apple itself
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
PICT
Use PICT when…
- Classic Mac OS Clipboard Data
- Legacy Macintosh Desktop Publishing (Aldus PageMaker, QuarkXPress)
- 1980s/1990s Digital Clip Art
T.38
Use T.38 when…
- Fax over IP (FoIP) Transmissions
- SIP/SDP Media Negotiation
- VoIP Gateways and PBX Systems
- Enterprise Fax Servers