pamdeinterlace - remove every other row from a PAM/PNM image
You can use the minimum unique abbreviation of the options. You can use two hyphens instead of one. You can separate an option name from its value with white space instead of an equals sign.
This program is part of Netpbm(1).
pamdeinterlace removes all the even-numbered or odd-numbered rows from the input PNM or PAM image. Specify which with the -takeeven and -takeodd options.
This can be useful if the image is a video capture from an interlaced video source. In that case, each row shows the subject 1/60 second before or after the two rows that surround it. If the subject is moving, this can detract from the quality of the image.
Because the resulting image is half the height of the input image, you will then want to use pamstretch or pamscale to restore it to its normal height:
pamdeinterlace myimage.ppm | pamstretch -yscale=2 >newimage.ppm
Another, usually better, way to deinterlace an image is with pammixinterlace.