ITU-R Recommenation BT.601, more commonly know by the abbreviations Rec. 601 or BT.601 or its former name, CCIR 601, is a standard published by the CCIR (now ITU-R) for encoding interlaced analogue video signals in digital form. It includes methods of encoding 525 line 60 Hz and 625-line 50 Hz signals, both with 720 luminance samples and 360 chrominance samples per line. The colour encoding system is known as YUV 4:2:2, that being the ratio of Y:Cb:Cr samples (luminance data:blue chroma data:red chroma data). For a pair of pixels, the data are stored in the order Y1:Y2:Cb:Cr, with the chrominance samples co-sited with the first luminance sample.