ppm3d - convert two portable pixmap into a red/blue 3d glasses pixmap
ppm3d leftppmfile rightppmfile [horizontal_offset]
Reads two portable pixmaps as input. Produces a portable pixmap as output, with the images overlapping by horizontal_offset
pixels in blue/red format.
horizontal_offset defaults to 30 pixels. Pixmaps MUST be the same size.
Copyright (C) 1993 by David K. Drum.