Image MIME Reference
APNG
Animated Portable Network Graphics
image/vnd.mozilla.apng
VS
Progressive JPEG (Legacy IE Alias)
image/pjpeg
PJPEG
A complete technical comparison of Animated Portable Network Graphics and Progressive JPEG (Legacy IE Alias) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | APNG | PJPEG |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | Yes | ✕ No |
| Progressive Loading | Yes | Yes |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | Yes | Yes |
| ICC Color Profile | Yes | Yes |
Animated Portable Network Graphics
image/vnd.mozilla.apng
Extension
.apng.png
Container
PNG Chunk Stream
Compression
Deflate (Lossless)
Algorithm
Deflate (zlib)
Color Depth
8-bit (Indexed), 24-bit (TrueColor), 32-bit (RGBA)
Developed by
Mozilla Corporation (Stuart Parmenter & Vladimir Vukićević)
Released
2004
Magic Bytes
89 50 4E 47 0D 0A 1A 0A
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 | APNG | PJPEG |
|---|---|---|
Chrome
|
✓ 59
|
✓ All
|
Firefox
|
✓ 3
|
✓ All
|
Safari
|
✓ 8
|
✓ All
|
Edge
|
✓ 79
|
✓ All
|
IE (Legacy)
|
✕ |
✓
|
APNG
APNG Strengths
- Supports 8-bit alpha transparency, completely solving the ugly 'white halo' problem inherent to GIFs
- Gracefully degrades; viewers that do not support APNG will render a perfectly valid, static PNG of the first frame
- Provides lossless compression that retains absolute pixel-perfect quality for UI elements and line art
Limitations
- Because it relies on lossless Deflate compression, file sizes for complex, video-like animations can be massive compared to lossy formats like WebP or AVIF
- Was initially rejected by the official PNG group, delaying its adoption for nearly a decade
- Lacks native hardware decoding acceleration, unlike video-based animated formats (like MP4 or WebM)
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
APNG
Use APNG when…
- High-Quality Web Animations
- Stickers (Apple iMessage, LINE, Discord)
- UI Loaders with Alpha Transparency
- GIF Replacement
PJPEG
Use PJPEG when…
- Legacy Internet Explorer File Uploads
- Progressive Image Rendering (Historical context)