An ITU-R standard for component digital video (YCbCr). It was designed to provide a common digital standard for interoperability between the three analog video/TV systems (NTSC, PAL and SECAM). ITU-R BT.601 enables their signals to be converted to digital and then easily converted back again to any of the three for distribution.
The choice of a luma sampling frequency of 13.5 MHz and a chroma frequency of 6.75MHz (4:2:2) yields 720 samples of active data per line for both NTSC and PAL/SECAM. See YUV, YCbCr and chroma subsampling.
BT.601 and BT.709
BT.601 was established in 1987 for 525-line (NTSC) and 625-line PAL/SECAM. In 1990, BT.709 was introduced for high definition (HDTV) with specifications for 1125 and 1250 lines. In 2000, BT.709-4 added 1080 lines to conform to the DTV standard. Following are the sampling frequencies used for both standards.
Luma Chroma
Standard Sampling Sampling
BT.601 SDTV 13.5 MHz 6.75 MHz (4:2:2)
BT.709 HDTV 74.25 MHz 37.125 MHz (4:2:2)
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