This program is part of Netpbm.
ppmtv reads a PPM image as input and dims every other row of image
data down by the specified dim factor. This factor may be in the
range of 0.0 (the alternate lines are totally black) to 1.0 (original
This creates an effect similar to what I've once seen in the video
clip 'You could be mine' by Guns'n'Roses. In the scene I'm talking
about you can see John Connor on his motorbike, looking up from the
water trench (?) he's standing in. While the camera pulls back, the
image gets 'normal' by brightening up the alternate rows of it. I
thought this would be an interesting effect to try in MPEG. I did not
yet check this out, however. Try for yourself.
Copyright (C) 1993 by Frank Neumann
netpbm documentation 16 November 1993 Ppmtv User Manual(0)