Image MIME Reference
PGM
Portable Graymap
image/x-portable-graymap
VS
Wireless Bitmap
image/vnd.wap.wbmp
WBMP
A complete technical comparison of Portable Graymap and Wireless Bitmap — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | PGM | WBMP |
|---|---|---|
| Transparency (Alpha) | ✕ No | ✕ No |
| 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)
Wireless Bitmap
image/vnd.wap.wbmp
Extension
.wbmp
Container
WBMP Type 0
Compression
Uncompressed
Algorithm
None
Color Depth
1-bit (Monochrome)
Developed by
WAP Forum (Now Open Mobile Alliance)
Released
1999
Magic Bytes
00 00
Browser Support Comparison
| Browser | PGM | WBMP |
|---|---|---|
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
WBMP
WBMP Strengths
- Extremely low processing overhead made it perfectly suited for the ultra-low-power CPUs of late 1990s mobile devices
- Tightly integrated into the WML (Wireless Markup Language) stack, enabling the first functional mobile internet experiences
Limitations
- Completely obsolete and lacks support in modern operating systems and browsers
- Limited entirely to 1-bit black and white (0 for black, 1 for white) with zero support for grayscale, color, or transparency
- The lack of a strong file header signature makes automated MIME type detection highly unreliable
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
WBMP
Use WBMP when…
- Legacy WML (Wireless Markup Language) Mobile Sites
- Early Mobile Phone Icons and Operator Logos
- Historical WAP Archival