This program is part of Netpbm.
This program is largely obsoleted by the more general pamfunc (use the -multiplier option). ppmdim remains for backward compatibility and also because its use of integer arithmetic may make it faster. ppmdim reads a PPM image input and diminishes its brightness by the specified dimfactor. The dimfactor may be in the range from 0.0 (total blackness, deep night, nada, null, nothing) to 1.0 (original picture's brightness).