Try File>>Save As with a type of 16-bit Grayscale PNG Height Files to save the current view as a grayscale height-coded image. Raw Binary file might also work for you. The bump map shader will shade the surface in the manner of an 8-bit height field that can be saved with any of the "Picture Files" types.

There is also the MDR and special MDR file formats as described at http://www.cartographersguild.com/sh...htmap-software.