Posted: 2006-09-22T13:12:49-07:00
Add -colors 256 to your command line to create a colormapped BMP image.
If you do not want -rotate to add extra colors to your image, but only use existing colors (some image degrading can occur) then you can use -interpolate nearest-neighbour setting before rotating. This is a new addition to IM and not yet fully documented in IM examples.
Also rather than -colors 256, you can re-map the colors to the original set of colors using
-map original.bmp. For more info on color reduction see the IM examples section of "Color Quantization and Dithering".