Image MIME Reference
CMU-Raster
CMU Window Manager Raster
image/x-cmu-raster
VS
JPEG Network Graphics
image/x-jng
JNG
A complete technical comparison of CMU Window Manager Raster and JPEG Network Graphics — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | CMU-Raster | JNG |
|---|---|---|
| Transparency (Alpha) | ✕ No | Yes |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | Yes |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | ✕ No | Yes |
| ICC Color Profile | ✕ No | Yes |
CMU Window Manager Raster
image/x-cmu-raster
Extension
.ras
Container
CMU Window Manager Bitmap
Compression
Uncompressed
Algorithm
None
Color Depth
1-bit (Monochrome), 8-bit (Indexed/Grayscale)
Developed by
Carnegie Mellon University (CMU)
Released
1980s
Magic Bytes
F1 00 40 BB
JPEG Network Graphics
image/x-jng
Extension
.jng
Container
PNG-style Chunk Structure (JHDR, JDAT, IDAT, IEND)
Compression
Lossy (JPEG/DCT for color) / Lossless (Deflate for alpha mask)
Algorithm
JPEG (Discrete Cosine Transform)Deflate (LZ77)
Color Depth
8-bit, 12-bit, 24-bit (RGB), 32-bit (RGBA)
Developed by
MNG Development Group (Glenn Randers-Pehrson et al.)
Released
2001
Magic Bytes
8B 4A 4E 47 0D 0A 1A 0A
Browser Support Comparison
| Browser | CMU-Raster | JNG |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
CMU-Raster
CMU-Raster Strengths
- Incredibly simple, uncompressed binary structure that was easy for early, memory-constrained UNIX workstations to parse and render
Limitations
- Completely obsolete and unsupported outside of niche historical command-line tools like Netpbm
- The shared '.ras' file extension causes frequent file misidentification and system conflicts
- Lacks all modern imaging features, including metadata, compression, and alpha channel transparency
JNG
JNG Strengths
- Solved a massive technical hurdle in the early 2000s by combining high-compression lossy photographic data with crisp, 8-bit alpha transparency
- Utilized the highly robust, extensible chunk-based architecture of the PNG format
- Provided an excellent, bandwidth-saving alternative to massive 32-bit transparent PNGs for web design
Limitations
- Failed to achieve critical mass; browser vendors largely abandoned the MNG/JNG standard due to implementation complexity
- Completely obsolete today, having been superseded by natively supported, superior formats like WebP, AVIF, and HEIC
- Decoding requires a hybrid engine that can parse PNG chunks while simultaneously decoding a JPEG stream and a Deflate stream, complicating software support
When to choose which format
CMU-Raster
Use CMU-Raster when…
- Historical UNIX / Andrew Project Archival
- Legacy Academic Computing Research
JNG
Use JNG when…
- Embedded frames in MNG animations
- Historical web graphics requiring lossy compression with transparency