Image MIME Reference
Epson-ERF
Epson Raw Format
image/x-epson-erf
VS
Portable Network Graphics (Legacy MIME)
image/x-png
PNG
A complete technical comparison of Epson Raw Format and Portable Network Graphics (Legacy MIME) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
PNG wins on browser support
Feature Support
| Feature | Epson-ERF | PNG |
|---|---|---|
| Transparency (Alpha) | ✕ No | Yes |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | Yes |
| HDR Support | Yes | Yes |
| EXIF Metadata | Yes | Yes |
| ICC Color Profile | ✕ No | Yes |
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 Network Graphics (Legacy MIME)
image/x-png
Extension
.png
Container
PNG Chunk Structure (IHDR, IDAT, IEND)
Compression
Deflate (Lossless)
Algorithm
Deflate (LZ77)
Color Depth
1-bit to 16-bit (Grayscale), 8-bit (Indexed Palette), 24-bit (True Color), 32-bit (True Color with Alpha), 48-bit (High Color), 64-bit (High Color with Alpha)
Developed by
PNG Development Group
Released
1996
Magic Bytes
89 50 4E 47 0D 0A 1A 0A
Browser Support Comparison
| Browser | Epson-ERF | PNG |
|---|---|---|
Chrome
|
✕ |
✓ 1
|
Firefox
|
✕ |
✓ 1
|
Safari
|
✕ |
✓ 1
|
Edge
|
✕ |
✓ 12
|
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
PNG
PNG Strengths
- The underlying format provides flawless, lossless compression and perfect 8-bit alpha channel transparency
- Universally supported by every modern operating system, image editor, and web browser
Limitations
- The 'image/x-png' string is an obsolete vendor quirk that forces backend developers to write redundant normalization logic in file upload scripts
- If left unnormalized, strict MIME validators or content security policies on modern systems may incorrectly reject valid PNG files
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
PNG
Use PNG when…
- Legacy Internet Explorer File Uploads
- Older ASP/PHP Web Applications
- Lossless Web Graphics