Image MIME Reference
PGM
Portable Graymap
image/x-portable-graymap
VS
Windows Metafile
image/x-wmf
WMF
A complete technical comparison of Portable Graymap and Windows Metafile — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | PGM | WMF |
|---|---|---|
| Transparency (Alpha) | ✕ No | Yes |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | ✕ No | ✕ No |
| ICC Color Profile | ✕ No | ✕ No |
Portable Graymap
image/x-portable-graymap
Extension
.pgm
Container
Netpbm
Compression
Uncompressed
Algorithm
None
Color Depth
8-bit (Grayscale), 16-bit (Grayscale)
Developed by
Jef Poskanzer (Netpbm Project)
Released
1988
Magic Bytes
50 32 (ASCII) or 50 35 (Binary)
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 | PGM | WMF |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ |
✓
|
PGM
PGM Strengths
- Extremely simple format allows custom parsers to be written from scratch in minimal time
- Supports 16-bit precision, making it highly valuable for scientific, medical, and height-map data where 8-bit precision is insufficient
- ASCII encoding ('P2') allows manual editing and visual inspection of pixel values directly within a text editor
Limitations
- Strictly limited to grayscale; cannot display color
- Lack of compression results in massive file sizes, making it entirely impractical for web delivery or consumer storage
- Does not support alpha transparency or modern metadata structures
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
PGM
Use PGM when…
- Computer Vision and Machine Learning Pre-processing
- Scientific and Medical Image Processing
- Unix/Linux Command-Line Image Pipelines
WMF
Use WMF when…
- Legacy Microsoft Office Clip Art and Icons
- Windows GDI Graphics Export
- Early Windows Desktop Publishing