The Digital Fact Book - Quantel

ITU-R BT.601This standard defines the digital encoding parameters of SD television for studios. It is theinternational standard for digitizing component television video in both 525 and 625 linesystems and is derived from SMPTE RP125. ITU-R BT.601 deals with both color difference(Y, R-Y, B-Y) and RGB component video and defines sampling systems, RGB/Y, R-Y, B-Ymatrix values and filter characteristics. It does not actually define the electro-mechanicalinterface – see ITU-R BT. 656.IITU-R BT.601 is normally taken to refer to color difference component digital video (ratherthan RGB), for which it defines 4:2:2 sampling at 13.5 MHz with 720 (4) luminance samplesper active line. The color difference signals R-Y and B-Y are sampled at 6.75 MHz with360 (2) samples per active line. Its depth may be 8 or 10 bits.Some headroom is allowed so, with 10-bit sampling, black level is at 64 (not 0) and whiteat level 940 (not 1023) – to minimize clipping of noise and overshoots. With 2 10 levelseach for Y (luminance), Cr and Cb (the digitized color difference signals) = 2 30 – over abillion unique colors can be defined.The sampling frequency of 13.5 MHz was chosen to provide a politically acceptable commonsampling standard between 525/60 and 625/50 systems, being a multiple of 2.25 MHz,the lowest common frequency to provide a static sampling pattern for both.See also: 13.5 MHz, 4:2:2, Frequency, Into digits (Tutorial 1)ITU-R BT.656The international standard for interconnecting digital television equipment operatingto the 4:2:2 standard defined in ITU-R BT.601. It defines blanking, embedded sync words,the video multiplexing formats used by both the parallel (now rare) and serial interfaces,the electrical characteristics of the interface and the mechanical details of the connectors.ITU-R BT.709In 2000, ITU-R BT.709-4 recommended the 1080 active line standard for 50 and 60 Hzinterlace scanning with sampling at 4:2:2 and 4:4:4. Actual sampling rates are 74.25 MHzfor luminance Y, or R, G, B and 37.125 MHz for color difference Cb and Cr, all at 8 bitsor 10 bits, and these should be used for all new productions. It also defines these 1080-linesquare-pixel standards as a common image formats (CIF) for international exchange.The original ITU-R BT.709 recommendation was for 1125/60 and 1250/50 (1035 and 1152active lines) HDTV formats defining values and a ‘4:2:2’ and ‘4:4:4’ sampling structure thatis 5.5 times that of ITU-R BT.601. Note that this is an ‘expanded’ form of 601 and so usesnon-square pixels.See also: Common Image Format114