This describes a set of sampling frequencies in the ratio 4:1:1, used to digitize the luminance and color difference components (Y, R-Y, B-Y) of a video signal. For SDTV the 4 represents 13.5 MHz (74.25 MHz for HDTV) sampling frequency of the Y (luminance) signal, and the 1’s are each 3.75 MHz for SD (18.5625 MHz for HD) for the R-Y and B-Y color difference signals (ie R-Y and B-Y are each sampled once for every four samples of Y).
With the color information sampled at half the rate of the 4:2:2 system, this is used as a more economic form of sampling that may be used where smaller data rates are required. Both luminance and color difference are still sampled on every line but the latter has half the horizontal resolution of 4:2:2 while the vertical resolution of the color information is maintained. 4:1:1 sampling is used in DVCPRO (625 and 525 formats), DVCAM (525/NTSC) and others.