pammixinterlace

Merge each row in an image with its two neighbours. See also: pamdeinterlace. More information: https://netpbm.sourceforge.net/doc/pammixinterlace.html.

pammixinterlace path/to/image.ppm > path/to/output.ppm

pammixinterlace -filter linear|fir|ffmpeg path/to/image.ppm > path/to/output.ppm

pammixinterlace -adaptive path/to/image.ppm > path/to/output.ppm