Before Netpbm release 10 (June 2002), this library was split into
four, and most of the documentation is still divided up that way:
Libraries by the above names no longer exist. All the above
subroutines are in libnetpbm.
The four interface header files, pbm.h, pgm.h,
ppm.h, pnm.h, however, still exist. You may use these,
but with the consolidation of the library, it is easier always to
use pam.h.
The documentation of the more general subroutines that don't deal
with image data directly, and whose names start with "pm", is
here.