Image MIME Reference
Apple-ICNS
Apple Icon Image
image/x-icns
VS
AirZip Accelerator Image
image/vnd.airzip.accelerator.azv
AZV
A complete technical comparison of Apple Icon Image and AirZip Accelerator Image — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | Apple-ICNS | AZV |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | Yes |
| 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
AirZip Accelerator Image
image/vnd.airzip.accelerator.azv
Extension
.azv
Container
Proprietary AirZip Container
Compression
Lossy (Proprietary) / Lossless (Proprietary)
Algorithm
AirZip Proprietary Compression
Color Depth
8-bit (Indexed), 24-bit (RGB)
Developed by
AirZip, Inc.
Released
1999
Magic Bytes
Unknown (Proprietary)
Browser Support Comparison
| Browser | Apple-ICNS | AZV |
|---|---|---|
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
AZV
AZV Strengths
- Historically allowed internet users to browse the web up to 5x faster over 56k dial-up modems by drastically reducing image payload sizes
- Officially registered in the IANA vendor tree, preventing MIME type conflicts on early web proxy servers
Limitations
- Completely obsolete in the modern broadband era
- Closed-source and proprietary, meaning no modern image manipulation libraries (like ImageMagick or libvips) can decode it
- Zero support in standard web browsers
When to choose which format
Apple-ICNS
Use Apple-ICNS when…
- macOS Application Bundles (.app)
- macOS Folder Customization
- Apple Disk Image (.dmg) Styling
AZV
Use AZV when…
- Dial-up Web Acceleration
- Bandwidth Optimization (Historical)
- Legacy Proxy Servers