ppmdim --version (return code: 0)
ppmdim: Using libpbm from Netpbm Version: Netpbm 10.0
ppmdim: BSD defined
ppmdim: RGB_ENV='RGBDEF'
ppmdim: RGBENV= 'RGBDEF' (env vbl is unset)
ppmdim -h (return code: 1)
usage: ppmdim dimfactor [ppmfile]
dimfactor: 0.0 = total blackness, 1.0 = original picture