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Image MIME Reference
Apple-ICNS

Apple Icon Image

image/x-icns
VS

AVC Image Sequence (HEIF Container)

image/avcs
AVCS

A complete technical comparison of Apple Icon Image and AVC Image Sequence (HEIF Container) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature Apple-ICNS AVCS
Transparency (Alpha) Yes Yes
Animation Support ✕ No Yes
Progressive Loading ✕ No ✕ No
HDR Support ✕ No Yes
EXIF Metadata ✕ No Yes
ICC Color Profile Yes Yes
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
Full Apple-ICNS reference →
AVC Image Sequence (HEIF Container)
image/avcs
Extension
.avcs.heifs
Container HEIF / ISOBMFF (ISO/IEC 14496-12)
Compression Lossy / Lossless
Algorithm
AVC (Advanced Video Coding / H.264)
Color Depth 8-bit, 10-bit, 12-bit
Developed by Moving Picture Experts Group (MPEG) / ISO/IEC JTC 1
Released 2015
Magic Bytes
XX XX XX XX 66 74 79 70 61 76 63 73
Full AVCS reference →

Browser Support Comparison

Browser Apple-ICNS AVCS
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE 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
AVCS

AVCS Strengths

  • Efficiently stores bursts of images or animations utilizing inter-frame compression
  • Leverages the highly compatible and widely hardware-accelerated AVC (H.264) codec
  • Robust HEIF container supports extensive metadata, alpha channels, and depth maps
Limitations
  • Zero native support in web browsers
  • Largely superseded in efficiency by newer sequence formats like HEICS (HEVC) or Animated AVIF (AV1)
  • Complicated container structure requires specialized parsing libraries

When to choose which format

Apple-ICNS
Use Apple-ICNS when…
  • macOS Application Bundles (.app)
  • macOS Folder Customization
  • Apple Disk Image (.dmg) Styling
AVCS
Use AVCS when…
  • Burst Photography
  • Short Animations
  • Camera Capture
  • Archival Storage

More comparisons

Apple-ICNS vs ACES → AVCS vs ACES → Apple-ICNS vs APNG → AVCS vs APNG → Apple-ICNS vs AVCI → AVCS vs AVCI → Apple-ICNS vs AVIF → AVCS vs AVIF → All comparisons →
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