Free webp to jpg
EN
Image MIME Reference
ICO

Windows Icon (Legacy MIME)

image/x-icon
VS

Microsoft Document Imaging

image/vnd.ms-modi
MODI

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

ICO wins on browser support

Feature Support

Feature ICO MODI
Transparency (Alpha) Yes ✕ No
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support ✕ No ✕ No
EXIF Metadata ✕ No ✕ No
ICC Color Profile ✕ No ✕ No
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 →
Microsoft Document Imaging
image/vnd.ms-modi
Extension
.mdi
Container TIFF Variant
Compression LZW / Proprietary MS Compression
Algorithm
LZW (Modified)
Color Depth 1-bit (Monochrome), 8-bit (Grayscale), 24-bit (RGB)
Developed by Microsoft Corporation
Released 2001
Magic Bytes
49 49 2A 00
Full MODI reference →

Browser Support Comparison

Browser ICO MODI
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
MODI

MODI Strengths

  • Historically provided an excellent all-in-one scanned document format with built-in OCR and annotations before PDF editing became universally accessible
  • Tightly integrated with Microsoft Office and SharePoint workflows in the early 2000s
Limitations
  • Completely proprietary and obsolete; Microsoft abandoned it in favor of standard TIFF and PDF
  • Causes widespread identification conflicts since its file signature is identical to a standard TIFF
  • Extremely difficult to open on modern operating systems without relying on third-party conversion utilities

When to choose which format

ICO
Use ICO when…
  • Website Favicons (favicon.ico)
  • Windows Application Executable Icons (.exe)
  • Desktop Shortcut Icons
MODI
Use MODI when…
  • Legacy Scanned Document Archival
  • Microsoft Office XP/2003/2007 Workflows
  • Embedded OCR Text Storage

More comparisons

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