Image MIME Reference
CMU-Raster
CMU Window Manager Raster
image/x-cmu-raster
VS
Windows Enhanced Metafile
image/x-emf
EMF
A complete technical comparison of CMU Window Manager Raster and Windows Enhanced Metafile — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | CMU-Raster | EMF |
|---|---|---|
| Transparency (Alpha) | ✕ No | Yes |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | ✕ No | ✕ No |
| 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
Windows Enhanced Metafile
image/x-emf
Extension
.emf
Container
Windows GDI/GDI+ Record Sequence
Compression
Uncompressed (Binary Drawing Records)
Algorithm
None
Color Depth
Vector (32-bit GDI/GDI+ Colors), Supports embedded 24-bit/32-bit bitmaps
Developed by
Microsoft Corporation
Released
1993
Magic Bytes
01 00 00 00 (Header Type) ... 20 45 4D 46 (Signature at offset 40)
Browser Support Comparison
| Browser | CMU-Raster | EMF |
|---|---|---|
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
EMF
EMF Strengths
- Device independent, meaning it renders consistently across different monitors and printers regardless of resolution
- Fully supports 32-bit precision and advanced GDI+ drawing commands, including alpha transparency and anti-aliasing (EMF+)
- Native rendering within the Windows OS ensures fast performance and flawless fidelity in Microsoft Office applications
Limitations
- Heavily tied to the Windows Graphics Device Interface API, making it notoriously difficult to parse perfectly on macOS or Linux
- Completely unsupported by modern web standards; cannot be embedded in HTML without conversion to SVG
- Security history: Like WMF, malicious drawing records can theoretically exploit vulnerabilities in older GDI parsers
When to choose which format
CMU-Raster
Use CMU-Raster when…
- Historical UNIX / Andrew Project Archival
- Legacy Academic Computing Research
EMF
Use EMF when…
- Microsoft Office Vector Graphics and Clip Art
- Windows Print Spooling (EMF Spool Files)
- High-fidelity Vector Interchange on Windows