A ratio of sampling frequencies used to digitise the luminance and colour difference components (Y, R-Y, B-Y) of a video signal. The term 4:2:2 denotes that for every four samples of Y, there are 2 samples each of R-Y and B-Y, giving more chrominance bandwidth in relation to luminance compared to 4:1:1 sampling.

ITU-R BT.601, 4:2:2 is the standard for digital studio equipment and the terms ‘4:2:2’ and ‘601’ are commonly (but technically incorrectly) used synonymously. The sampling frequency of Y is 13.5 MHz and that of R-Y and B-Y is each 6.75 MHz, providing a maximum colour bandwidth of 3.37 MHz – enough for high quality chroma keying. For HD the sampling rates are 5.5 times greater, 74.25 MHz forY, and 37.125 MHz forR-Y and B-Y.

See also: Co-sited sampling, Digital keying, ITU-R BT.601, ITU-R BT.709, Nyquist