Image MIME Reference
Generic-RAW
Digital Camera Raw (Generic Linux MIME)
image/x-dcraw
VS
Windows Metafile
image/x-wmf
WMF
A complete technical comparison of Digital Camera Raw (Generic Linux MIME) and Windows Metafile — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | Generic-RAW | WMF |
|---|---|---|
| Transparency (Alpha) | ✕ No | Yes |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | Yes | ✕ No |
| ICC Color Profile | Yes | ✕ No |
Digital Camera Raw (Generic Linux MIME)
image/x-dcraw
Extension
.raw
Container
Varies (Predominantly TIFF/EP)
Compression
Lossless / Uncompressed
Algorithm
Varies (Often Lossless JPEG ITU-T81 or uncompressed)
Color Depth
12-bit, 14-bit, 16-bit
Developed by
freedesktop.org (MIME mapping) / Dave Coffin (dcraw tool)
Released
1997
Magic Bytes
Varies by vendor format
Windows Metafile
image/x-wmf
Extension
.wmf.emf
Container
Windows GDI Metafile Command Stream
Compression
Uncompressed (Command Stream)
Algorithm
None
Color Depth
Varies based on GDI rendering engine
Developed by
Microsoft Corporation
Released
1990
Magic Bytes
D7 CD C6 9A (Aldus Placeable Metafile Header) or 01 00 09 00 (Standard WMF Header)
Browser Support Comparison
| Browser | Generic-RAW | WMF |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ |
✓
|
Generic-RAW
Generic-RAW Strengths
- Provides a unified, highly useful catch-all MIME type for application developers who just need to know if a file is a raw image, rather than tracking 50+ individual camera extensions
- Deeply integrated into the Linux desktop ecosystem, ensuring file manager thumbnails work seamlessly via tools like ufraw-thumbnailer
Limitations
- Not an official IANA standard
- Can cause conflicts where standard TIFF files are misidentified as raw camera data by over-aggressive MIME sniffers
- The underlying 'dcraw' tool was abandoned by its creator in 2018 (though its successor, LibRaw, continues to maintain the ecosystem)
WMF
WMF Strengths
- Infinitely scalable vector format that remains remarkably compact for simple geometric illustrations and charts
- Historically served as a seamless conduit for copying and pasting vector graphics between disparate Windows applications via the system clipboard
Limitations
- Notoriously plagued by historic security vulnerabilities, making raw WMF parsing a vector for exploits in legacy software
- Completely obsolete and unsupported in modern web environments (browsers cannot render them)
- Strictly tied to the Windows GDI architecture, making cross-platform rendering inconsistent across Linux and macOS
When to choose which format
Generic-RAW
Use Generic-RAW when…
- Linux Desktop File Associations (GNOME/KDE)
- Thumbnail Generation for Raw Images (UFRaw/LibRaw)
- Server-side Image Processing Fallbacks
WMF
Use WMF when…
- Legacy Microsoft Office Clip Art and Icons
- Windows GDI Graphics Export
- Early Windows Desktop Publishing