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