Image MIME Reference
Apple-ICNS
Apple Icon Image
image/x-icns
VS
X Bitmap (Legacy MIME Alias)
image/x-xbm
XBM
A complete technical comparison of Apple Icon Image and X Bitmap (Legacy MIME Alias) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | Apple-ICNS | XBM |
|---|---|---|
| Transparency (Alpha) | Yes | Yes |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | ✕ No | ✕ No |
| ICC Color Profile | Yes | ✕ No |
Apple Icon Image
image/x-icns
Extension
.icns
Container
Chunk-based (OSType Header)
Compression
Uncompressed (Legacy) / PNG (Modern) / JPEG 2000 (Modern)
Algorithm
NoneDeflate (via embedded PNG)Wavelet (via embedded JP2)
Color Depth
1-bit (Monochrome), 4-bit, 8-bit, 24-bit (RGB), 32-bit (RGBA)
Developed by
Apple Inc.
Released
2001
Magic Bytes
69 63 6E 73
X Bitmap (Legacy MIME Alias)
image/x-xbm
Extension
.xbm
Container
C Source Code Header (.h)
Compression
Uncompressed (Source Code)
Algorithm
None
Color Depth
1-bit (Monochrome)
Developed by
MIT / X Consortium (X Window System)
Released
1988
Magic Bytes
23 64 65 66 69 6e 65 (ASCII '#define')
Browser Support Comparison
| Browser | Apple-ICNS | XBM |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ |
✓
|
Apple-ICNS
Apple-ICNS Strengths
- Seamlessly handles multi-resolution scaling on macOS, perfectly serving both standard and high-DPI (Retina) displays from a single asset
- Modern versions efficiently embed standard PNG files, making it much easier to parse the high-resolution layers than the legacy raw pixel formats
Limitations
- Strictly bound to the Apple ecosystem; completely useless natively on Windows, Linux, or the Web
- The internal chunking structure is notoriously messy, utilizing dozens of different undocumented, legacy OSType tags spanning 20+ years of Apple history
XBM
XBM Strengths
- Can be compiled directly into C or C++ source code without needing an external file loader or binary asset manager
- Human-readable structure allows developers to inspect, edit, or hand-craft tiny icons directly within a text editor
- Extremely predictable and lightweight for 1-bit hardware displays and embedded systems
Limitations
- Strictly limited to 1-bit monochrome (black and white) graphics with no gray or color support
- Text-based C syntax creates massive file bloat compared to binary 1-bit formats like PBM
- Completely deprecated in modern web browsers and desktop GUI frameworks
When to choose which format
Apple-ICNS
Use Apple-ICNS when…
- macOS Application Bundles (.app)
- macOS Folder Customization
- Apple Disk Image (.dmg) Styling
XBM
Use XBM when…
- X Window System (X11) Cursors and Icons
- Embedded C/C++ Firmware UI Assets
- Early 1990s Unix Web Graphics