Free webp to jpg
EN
Image MIME Reference
DGN

MicroStation Design File

image/x-vnd.dgn
VS

Portable Graymap

image/x-portable-graymap
PGM

A complete technical comparison of MicroStation Design File and Portable Graymap — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature DGN PGM
Transparency (Alpha) Yes ✕ No
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support ✕ No Yes
EXIF Metadata ✕ No ✕ No
ICC Color Profile ✕ No ✕ No
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 →
Portable Graymap
image/x-portable-graymap
Extension
.pgm
Container Netpbm
Compression Uncompressed
Algorithm
None
Color Depth 8-bit (Grayscale), 16-bit (Grayscale)
Developed by Jef Poskanzer (Netpbm Project)
Released 1988
Magic Bytes
50 32 (ASCII) or 50 35 (Binary)
Full PGM reference →

Browser Support Comparison

Browser DGN PGM
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
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
PGM

PGM Strengths

  • Extremely simple format allows custom parsers to be written from scratch in minimal time
  • Supports 16-bit precision, making it highly valuable for scientific, medical, and height-map data where 8-bit precision is insufficient
  • ASCII encoding ('P2') allows manual editing and visual inspection of pixel values directly within a text editor
Limitations
  • Strictly limited to grayscale; cannot display color
  • Lack of compression results in massive file sizes, making it entirely impractical for web delivery or consumer storage
  • Does not support alpha transparency or modern metadata structures

When to choose which format

DGN
Use DGN when…
  • Civil Engineering and Plant Design
  • Large-scale Architecture and Construction (AEC)
  • 2D/3D Infrastructure Modeling
PGM
Use PGM when…
  • Computer Vision and Machine Learning Pre-processing
  • Scientific and Medical Image Processing
  • Unix/Linux Command-Line Image Pipelines

More comparisons

DGN vs ACES → PGM vs ACES → DGN vs APNG → PGM vs APNG → DGN vs AVCI → PGM vs AVCI → DGN vs AVCS → PGM vs AVCS → DGN vs AVIF → PGM vs AVIF → All comparisons →
Share this comparison