TESAnnwyn -p 1 -b 32 -s 1.5 -w Tamriel Skyrim.esm
I used these settings, and opened the result with IrfanView:
http://img197.imageshack.us/img197/7633/skyrimtestprometheus.png
...one has to specify the dimensions and the depth (32 bit). The remaining options I left unchanged. The picture is flipped, so north is at the bottom edge, and the red area is the mountains in the south
Keep in mind that the colorscale is meaningless in a raw file (even in the bmp file). It is just a signed 32-int encoded as a "color"