Image MIME Reference
IEF
Image Exchange Format
image/ief
VS
Progressive JPEG (Legacy IE Alias)
image/pjpeg
PJPEG
A complete technical comparison of Image Exchange Format and Progressive JPEG (Legacy IE Alias) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
PJPEG wins on browser support
Feature Support
| Feature | IEF | PJPEG |
|---|---|---|
| Transparency (Alpha) | ✕ No | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | Yes |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | ✕ No | Yes |
| ICC Color Profile | ✕ No | Yes |
Image Exchange Format
image/ief
Extension
.ief
Container
TIFF Class B (TIFF-B)
Compression
Lossless (MH, MR, MMR) / Uncompressed
Algorithm
MHMRMMRUncompressed
Color Depth
1-bit (Monochrome)
Developed by
IETF Network Fax Working Group
Released
1992
Magic Bytes
49 49 2A 00 (Little-endian) / 4D 4D 00 2A (Big-endian)
Progressive JPEG (Legacy IE Alias)
image/pjpeg
Extension
.jpeg.jpg.pjpeg.pjp.jfif
Container
JPEG (ISO/IEC 10918-1)
Compression
Lossy (DCT)
Algorithm
Discrete Cosine Transform (DCT)
Color Depth
8-bit, 12-bit
Developed by
Joint Photographic Experts Group / Microsoft (Alias)
Released
1992
Magic Bytes
FF D8 FF E0 (JFIF) / FF D8 FF E1 (Exif)
Browser Support Comparison
| Browser | IEF | PJPEG |
|---|---|---|
Chrome
|
✕ |
✓ All
|
Firefox
|
✕ |
✓ All
|
Safari
|
✕ |
✓ All
|
Edge
|
✕ |
✓ All
|
IE (Legacy)
|
✕ |
✓
|
IEF
IEF Strengths
- Provided a standard method for exchanging bi-level fax images during the early days of the Internet
- Supported multi-page documents
- Leveraged the highly resilient and well-documented TIFF container
Limitations
- Completely obsolete and unsupported in modern computing environments
- Strictly limited to 1-bit monochrome data, lacking color or grayscale capabilities
- Magic bytes overlap completely with standard TIFF, making specific filetype detection difficult without parsing internal tags
PJPEG
PJPEG Strengths
- Progressive JPEGs (which this MIME type attempted to describe) provide excellent perceived loading speeds on slow connections by rendering a low-resolution preview first
- Files sent with this MIME type are fully backwards compatible with any standard JPEG decoder
Limitations
- It is a non-standard MIME type that violates IANA specifications
- Causes strict file upload validation scripts to fail if not explicitly whitelisted or mapped
- Creates unnecessary confusion, as the official image/jpeg MIME type already fully encompasses progressive encoding
When to choose which format
IEF
Use IEF when…
- Legacy Fax Transmissions
- Early Internet Gateways
- Archival
PJPEG
Use PJPEG when…
- Legacy Internet Explorer File Uploads
- Progressive Image Rendering (Historical context)