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Image MIME Reference
BMP

Windows Bitmap (Legacy Windows MIME Alias)

image/x-windows-bmp
VS

MicroStation Design File

image/x-vnd.dgn
DGN

A complete technical comparison of Windows Bitmap (Legacy Windows MIME Alias) and MicroStation Design File — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

BMP wins on browser support

Feature Support

Feature BMP DGN
Transparency (Alpha) Yes Yes
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support ✕ No ✕ No
EXIF Metadata ✕ No ✕ No
ICC Color Profile Yes ✕ No
Windows Bitmap (Legacy Windows MIME Alias)
image/x-windows-bmp
Extension
.bmp.dib
Container DIB (Device-Independent Bitmap)
Compression Uncompressed / Run-Length Encoding (RLE)
Algorithm
NoneRLE4RLE8
Color Depth 1-bit (Monochrome), 4-bit (16 colors), 8-bit (256 colors), 16-bit (High Color), 24-bit (True Color), 32-bit (True Color with Alpha)
Developed by Microsoft Corporation
Released 1985
Magic Bytes
42 4D
Full BMP reference →
MicroStation Design File
image/x-vnd.dgn
Extension
.dgn
Container Microsoft OLE Compound File (V8) / IGDS (V7)
Compression Uncompressed / OLE Structured Storage
Algorithm
None
Color Depth Indexed Color (V7), 24-bit True Color (V8)
Developed by Intergraph (Originally) / Bentley Systems (Currently)
Released 1980
Magic Bytes
D0 CF 11 E0 A1 B1 1A E1 (For V8 DGN)
Full DGN reference →

Browser Support Comparison

Browser BMP DGN
Chrome Chrome
✓ 1
 ✕
Firefox Firefox
✓ 1
 ✕
Safari Safari
✓ 1
 ✕
Edge Edge
✓ 12
 ✕
IE IE (Legacy)
✓
 ✕
BMP

BMP Strengths

  • Universally supported by all major operating systems and modern web browsers
  • Maintains perfect, lossless fidelity because pixel data is stored without lossy compression artifacts
Limitations
  • Massive file size overhead due to a lack of modern compression algorithms
  • Legacy MIME strings like 'image/x-windows-bmp' can trigger validation warnings in strict security or API environments if unhandled
DGN

DGN Strengths

  • Exceptionally robust at handling massive, coordinate-heavy infrastructure models that would frequently crash older versions of competing CAD software
  • Deeply entrenched as the absolute standard format for many global departments of transportation and civil engineering firms
  • V8 architecture supports boundless design plane coordinates, eliminating the physical scaling limitations of V7
Limitations
  • Deeply proprietary format requiring complex third-party libraries (like the ODA SDK) to parse or write programmatically outside of the Bentley ecosystem
  • V8's reliance on the archaic Microsoft OLE Compound File container makes file introspection cumbersome
  • Cannot be rendered natively in web browsers without converting to WebGL/Canvas formats or SVG

When to choose which format

BMP
Use BMP when…
  • Legacy Windows Desktop Registry Associations
  • Older Enterprise Intranet Applications
  • Windows Graphics Archival
DGN
Use DGN when…
  • Civil Engineering and Plant Design
  • Large-scale Architecture and Construction (AEC)
  • 2D/3D Infrastructure Modeling

More comparisons

BMP vs ACES → DGN vs ACES → BMP vs APNG → DGN vs APNG → BMP vs AVCI → DGN vs AVCI → BMP vs AVCS → DGN vs AVCS → BMP vs AVIF → DGN vs AVIF → All comparisons →
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