In 2000, ITU-R BT.709-4 recommended the 1080 active-line high definition television standard for 50 and 60 Hz interlace scanning with sampling at 4:2:2 and 4:4:4. Actual sampling rates are 74.25 MHz for luminance Y, or R, G, B and 37.125 MHz for color difference Cb and Cr, all at 8 bits or 10 bits, and these should be used for all new productions. It also defines these 1080-line square-pixel standards as common image formats (CIF) for international exchange.
The original ITU-R BT.709 recommendation was for 1125/60 and 1250/50 (1035 and 1152 active lines) HDTV formats defining values and a ‘4:2:2’ and ‘4:4:4’ sampling structure that is 5.5 times that of ITU-R BT.601. Note that this is an ‘expanded’ form of 601 and so uses non-square pixels.
See also: Common Image Format