Image MIME Reference
ICO
Windows Icon (Legacy MIME)
image/x-icon
VS
Panasonic RAW Image
image/x-panasonic-raw
Panasonic-RAW-(RW2)
A complete technical comparison of Windows Icon (Legacy MIME) and Panasonic RAW Image — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
ICO wins on browser support
Feature Support
| Feature | ICO | Panasonic-RAW-(RW2) |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | Yes |
| EXIF Metadata | ✕ No | Yes |
| ICC Color Profile | ✕ No | Yes |
Windows Icon (Legacy MIME)
image/x-icon
Extension
.ico
Container
ICO Directory Structure
Compression
Uncompressed (DIB/BMP) / Deflate (Embedded PNG)
Algorithm
NoneDeflate (via PNG)
Color Depth
1-bit, 4-bit, 8-bit, 24-bit (True Color), 32-bit (RGBA)
Developed by
Microsoft Corporation
Released
1985
Magic Bytes
00 00 01 00
Panasonic RAW Image
image/x-panasonic-raw
Extension
.raw.rw2
Container
TIFF-based (Proprietary)
Compression
Uncompressed / Panasonic Proprietary Lossless
Algorithm
NoneProprietary Lossless
Color Depth
12-bit (Per Channel), 14-bit (Per Channel), 16-bit (Per Channel - High-res mode)
Developed by
Panasonic Corporation
Released
2004
Magic Bytes
Older RAW: 49 49 2A 00 | Newer RW2: 49 49 55 00
Browser Support Comparison
| Browser | ICO | Panasonic-RAW-(RW2) |
|---|---|---|
Chrome
|
✓ 1
|
✕ |
Firefox
|
✓ 1
|
✕ |
Safari
|
✓ 1
|
✕ |
Edge
|
✓ 12
|
✕ |
IE (Legacy)
|
✓
|
✕ |
ICO
ICO Strengths
- Universally supported by every web browser in existence for website favicons
- Packs multiple resolutions into a single file, eliminating the need to serve different files for the taskbar vs. the desktop
- Modern support for embedded PNGs (since Windows Vista) allows for excellent 32-bit transparency (alpha channels) and drastically reduced file sizes
Limitations
- Internal file structure is convoluted due to decades of legacy cruft, such as the requirement for BMP data to lack a standard file header but double the height property for an archaic XOR/AND mask
- Larger file size compared to a single optimized PNG or SVG, as it literally stores the same image multiple times at different scales
- The MIME type landscape is highly fragmented (x-icon vs. vnd.microsoft.icon), causing occasional caching or strict-MIME validation errors on restrictive servers
Panasonic-RAW-(RW2)
Panasonic-RAW-(RW2) Strengths
- Retains maximum sensor data, allowing significant recovery of highlights and shadows compared to in-camera JPEGs
- Modern RW2 files embed proprietary lens correction profiles (distortion, vignetting, chromatic aberration) that raw converters can automatically apply
- The unique 'IIU' signature on RW2 files makes programmatic identification extremely reliable compared to other TIFF-spoofing raw formats
Limitations
- Proprietary format requires continuous updates to third-party processing engines whenever Panasonic releases a new Lumix camera
- Produces very large file sizes, particularly when using Panasonic's High-Resolution multi-shot modes
- Cannot be directly embedded into web pages or used in standard HTML/CSS contexts
When to choose which format
ICO
Use ICO when…
- Website Favicons (favicon.ico)
- Windows Application Executable Icons (.exe)
- Desktop Shortcut Icons
Panasonic-RAW-(RW2)
Use Panasonic-RAW-(RW2) when…
- Professional Digital Photography
- Non-destructive Image Post-Processing
- High Dynamic Range (HDR) Lumix Archival