Image MIME Reference
AVIF
AV1 Image File Format
image/avif
VS
Progressive JPEG (Legacy IE Alias)
image/pjpeg
PJPEG
A complete technical comparison of AV1 Image File 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 | AVIF | PJPEG |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | Yes | ✕ No |
| Progressive Loading | ✕ No | Yes |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | Yes | Yes |
| ICC Color Profile | Yes | Yes |
AV1 Image File Format
image/avif
Extension
.avif
Container
HEIF / ISOBMFF
Compression
AV1 Lossy / AV1 Lossless
Algorithm
AV1
Color Depth
8-bit, 10-bit, 12-bit
Developed by
Alliance for Open Media (AOMedia)
Released
2019
Magic Bytes
XX XX XX XX 66 74 79 70 61 76 69 66
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 | AVIF | PJPEG |
|---|---|---|
Chrome
|
✓ 85+
|
✓ All
|
Firefox
|
✓ 93+
|
✓ All
|
Safari
|
✓ 16+
|
✓ All
|
Edge
|
✓ 121+
|
✓ All
|
IE (Legacy)
|
✕ |
✓
|
AVIF
AVIF Strengths
- Best-in-class compression — typically 20–50% smaller than WebP at equivalent quality
- Native HDR and wide color gamut (BT.2020) support
- Supports 8, 10, and 12-bit color depth
Limitations
- Encoding is highly CPU-intensive — significantly slower than JPEG or WebP
- Requires Edge 121+ (not supported in earlier Edge versions)
- Limited support in native desktop image viewers
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
AVIF
Use AVIF when…
- Next-Gen Websites
- HDR Photography
- High-Quality Web Images
PJPEG
Use PJPEG when…
- Legacy Internet Explorer File Uploads
- Progressive Image Rendering (Historical context)