DGN (also RDL) is a file format common to Intergraph's MicroStation and Interactive Graphics Design System (IGDS) CAD applications running on Intergraph workstations and PCs. 
Blaze ImgConvert supports DGN versions 1, 2 and 3.
Blaze ImgConvert can load the following objects: Line (Type 3), Polyline (Type 4), Polyline (Type 6), Polyline (Type 11), Polyline (Type 21), Ellipse (Type 15), Arc (Type 16), and Text (Type 17).
For DGN files, you can read the following bits per pixel: 24.