a) Picture element with equal vertical and horizontal sample spacing, having an aspect ratio of 1:1. Square pixels are used by computers, and the software expects the use of square pixels for proper operation.

Video originally was unconcerned about the aspect ratio of its pixels.

Increasing dependence upon electronic post-production has emphasized the advantage of square pixels. b) System M/NTSC, by comparison, does not have square pixels. With 485 active vertical lines per frame, and 768 samples per active horizontal line (when sampled at four times subcarrier) in a 4:3 aspect ratio, the resulting pixels have an aspect ratio (width:height) of 0.842. c) During image processing, some transforms that manipulate individual pixels as independent picture elements - especially those operations involving any image rotation, distortion, or size changes are performed with simplified programs and less risk of artifacts when the pixels are square.