A sampling system used to digitise the luminance and colour difference components (Y, R-Y, B-Y) of a video signal. The 4 represents the 13.5 MHz (74.25 MHz at HD) sampling frequency of Y while the R-Y and B-Y are sampled at 6.75 MHz (37.125 MHz) – effectively between every other line only (ie one line is sampled at 4:0:0, luminance only, and the next at 4:2:2).

This is used in some 625 line systems where video data rate needs to be reduced. It decreases data by 25 percent against 4:2:2 sampling and the colour information has a reasonably even resolution in both the vertical and horizontal directions. 4:2:0 is widely used in MPEG-2 and 625 DV and DVCAM.

See also: 4:1:1, 4:2:2, DVCAM, MPEG-2