Image MIME Reference
Epson-ERF
Epson Raw Format
image/x-epson-erf
VS
Portable Anymap
image/x-portable-anymap
PNM
A complete technical comparison of Epson Raw Format and Portable Anymap — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | Epson-ERF | PNM |
|---|---|---|
| Transparency (Alpha) | ✕ No | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | Yes | ✕ No |
| ICC Color Profile | ✕ No | ✕ No |
Epson Raw Format
image/x-epson-erf
Extension
.erf
Container
TIFF/EP
Compression
Uncompressed / Lossless JPEG (ITU-T81)
Algorithm
NoneLossless JPEG
Color Depth
12-bit (Per Channel)
Developed by
Seiko Epson Corporation
Released
2004
Magic Bytes
49 49 2A 00 or 4D 4D 00 2A
Portable Anymap
image/x-portable-anymap
Extension
.pnm
Container
Netpbm
Compression
Uncompressed
Algorithm
None
Color Depth
1-bit (PBM), 8-bit to 16-bit (PGM), 24-bit to 48-bit (PPM)
Developed by
Jef Poskanzer (Netpbm Project)
Released
1988
Magic Bytes
50 31, 50 32, 50 33, 50 34, 50 35, or 50 36
Browser Support Comparison
| Browser | Epson-ERF | PNM |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
Epson-ERF
Epson-ERF Strengths
- Preserves original raw sensor data, allowing extreme recovery of highlights and shadows compared to in-camera JPEGs
- Utilizes the standard TIFF container structure, making it relatively easy for open-source software (like dcraw and LibRaw) to parse and decode
Limitations
- Completely obsolete proprietary format tied to a defunct line of digital cameras
- Requires parsing EXIF metadata to differentiate it from standard TIFF files programmatically
- Cannot be natively viewed in web browsers or standard operating system image viewers without specialized codecs
PNM
PNM Strengths
- Unparalleled simplicity: parsers and writers for PNM files can be written from scratch in C or Python in just a few minutes without relying on external libraries
- Serves as an excellent foundational teaching tool for computer science students learning about image arrays and raster graphics
- Flawlessly pipes through Unix command-line utilities for robust automated image processing (via the Netpbm suite)
Limitations
- Zero compression natively results in astronomical file sizes, making it entirely impractical for web delivery or consumer storage
- No support for standard metadata formats like EXIF, XMP, or ICC color profiles
- No native alpha channel support in the classic PNM specification (though the newer PAM format 'P7' addresses this)
When to choose which format
Epson-ERF
Use Epson-ERF when…
- Vintage Digital Photography (Epson R-D1)
- Non-destructive Image Post-Processing
- Raw Imaging Archival
PNM
Use PNM when…
- Unix/Linux Command-Line Image Processing (Netpbm suite)
- Academic Computer Vision Research
- Intermediary Format for Image Format Conversion