NAMEppmdim - dim a portable pixmap down to total blackness
SYNOPSISppmdim dimfactor [ppmfile]
DESCRIPTIONReads a portable pixmap as input. Diminishes its brightness by the specified dimfactor down to total blackness. The dimfactor may be in the range from 0.0 (total blackness, deep night, nada, null, nothing) to 1.0 (original picture's brightness).
As pnmgamma does not do the brightness correction in the way I wanted it, this small program was written.
ppmdim is similar to ppmbrighten , but not exactly the same.