Free webp to jpg
EN
Image MIME Reference
ICO

Windows Icon (Legacy MIME)

image/x-icon
VS

TIFF for Facsimile eXtended

image/tiff-fx
TIFF-FX

A complete technical comparison of Windows Icon (Legacy MIME) and TIFF for Facsimile eXtended — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

ICO wins on browser support

Feature Support

Feature ICO TIFF-FX
Transparency (Alpha) Yes ✕ No
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support ✕ No ✕ No
EXIF Metadata ✕ No ✕ No
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
Full ICO reference →
TIFF for Facsimile eXtended
image/tiff-fx
Extension
.tiff.tif
Container TIFF 6.0 Tag Directory Structure
Compression MH / MR / MMR (CCITT Group 3 & 4) / JBIG / JPEG
Algorithm
CCITT Group 3/4JBIGJPEG
Color Depth 1-bit (Monochrome B&W), 8-bit (Grayscale/Color Indexed), 24-bit (RGB Color)
Developed by IETF (Internet Engineering Task Force)
Released 1998
Magic Bytes
49 49 2A 00 (Little-Endian) / 4D 4D 00 2A (Big-Endian)
Full TIFF-FX reference →

Browser Support Comparison

Browser ICO TIFF-FX
Chrome Chrome
✓ 1
 ✕
Firefox Firefox
✓ 1
 ✕
Safari Safari
✓ 1
 ✕
Edge Edge
✓ 12
 ✕
IE 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
TIFF-FX

TIFF-FX Strengths

  • Provides a universal, standardized format for transmitting multi-page documents over IP networks and email (Internet Fax)
  • Supports highly efficient telecom-centric compression algorithms (MMR, JBIG) that produce very small files for text documents
  • Maintains backwards compatibility with standard TIFF parsers
Limitations
  • Not supported natively by web browsers
  • Requires complex parsing of TIFF IFD tags to differentiate a true TIFF-FX file from a standard TIFF file
  • Usage is slowly declining as traditional faxing is replaced by secure PDF transmission and e-signature platforms

When to choose which format

ICO
Use ICO when…
  • Website Favicons (favicon.ico)
  • Windows Application Executable Icons (.exe)
  • Desktop Shortcut Icons
TIFF-FX
Use TIFF-FX when…
  • Internet Fax (T.37)
  • Enterprise Fax Servers
  • Document Archiving
  • Telecommunications

More comparisons

ICO vs ACES → TIFF-FX vs ACES → ICO vs APNG → TIFF-FX vs APNG → ICO vs AVCI → TIFF-FX vs AVCI → ICO vs AVCS → TIFF-FX vs AVCS → ICO vs AVIF → TIFF-FX vs AVIF → All comparisons →
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