The -headersize flag is to get around an apparent shortcoming in some implementations of the MacPaint format. According to the spec, the header size is supposed to be 512, and this is the default; however, some implementations use 640, or other values. The symptom to watch for is that the resulting PBM file looks shifted to one side. If you get this, try -h 640, and if that still doesn't look right try another value.
All flags can be abbreviated to their shortest unique prefix.
Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. This software is provided "as is" without express or implied warranty.
The MacPaint-reading code is Copyright (c) 1987 by Patrick J. Naughton (naughton@wind.sun.com)
Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation.