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Image MIME Reference
HEIC

High Efficiency Image Container

image/heic
VS

Windows Icon (Legacy MIME)

image/x-icon
ICO

A complete technical comparison of High Efficiency Image Container and Windows Icon (Legacy MIME) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

ICO wins on browser support

Feature Support

Feature HEIC ICO
Transparency (Alpha) Yes Yes
Animation Support Yes ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes ✕ No
EXIF Metadata Yes ✕ No
ICC Color Profile Yes ✕ No
High Efficiency Image Container
image/heic
Extension
.heic
Container HEIF / ISOBMFF
Compression Lossy / Lossless
Algorithm
HEVC (H.265)
Color Depth 8-bit, 10-bit, 12-bit, 16-bit
Developed by MPEG (Standard) / Apple (Adoption)
Released 2017
Magic Bytes
XX XX XX XX 66 74 79 70 68 65 69 63
Full HEIC reference →
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
Full ICO reference →

Browser Support Comparison

Browser HEIC ICO
Chrome Chrome
✕
✓ 1
Firefox Firefox
✕
✓ 1
Safari Safari
✓ 11+
✓ 1
Edge Edge
✕
✓ 12
IE IE (Legacy)
✕
✓
HEIC

HEIC Strengths

  • Exceptional compression efficiency — stores images at roughly half the file size of JPEG with equal or better visual quality
  • Natively supports modern photography features like depth maps, 16-bit color, HDR, and alpha channel transparency
  • Can store image bursts, focal stacks, and animations (Live Photos) within a single file
Limitations
  • Heavily encumbered by software patents, leading to very poor adoption outside the Apple ecosystem
  • Not supported by standard web browsers (except Safari), requiring server-side or client-side conversion for web delivery
  • Windows requires downloading a separate (often paid) extension from the Microsoft Store to view natively
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

When to choose which format

HEIC
Use HEIC when…
  • iOS / iPhone Photography
  • macOS Ecosystem
  • High-Quality Image Archiving
ICO
Use ICO when…
  • Website Favicons (favicon.ico)
  • Windows Application Executable Icons (.exe)
  • Desktop Shortcut Icons

More comparisons

HEIC vs ACES → ICO vs ACES → HEIC vs APNG → ICO vs APNG → HEIC vs AVCI → ICO vs AVCI → HEIC vs AVCS → ICO vs AVCS → HEIC vs AVIF → ICO vs AVIF → All comparisons →
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