CCIR Recommendation 656 (1986) provides interface standards picture redundancy and complex coding strategies can provide very for digital parallel working at 27Mbit/s and serial working at large degrees of bit rate reduction without excessively increasing 243Mbit/s in fully digital areas. the harmful effects of bit errors. However, once large bit rate Experience with digital video processing has shown that 8 bit reduction has been applied, it becomes impracticable to use such PCM is not considered by some manufacturers as adequate for all production techniques as chroma keying 'downstream' of the bit intermediate interconnections within a processing chain. One result rate reduction. is that a de facto standard of 10 bits exists, which makes use of the Television transmission 57/13 Table 57.4 Major parameters of the digital component standard CCIR Recommendation 601 (1982): 4:2:2 standard Luminance (Y) Colour difference signals (R-Y) (B-Y) Sampling frequency (MHz) Bandwidth (analogue) (MHz) 5.75 (+0.1 depending on 2.75 (+0, -1 depending on sampling filters) sampling filters) Form of coding Uniformly quantized PCM 8 bits per sample for Y, R-Y and B-Y Coded signals representing Samples per total line: 625-50 systems 525-60 systems Samples per active line: 625-50 systems 525-60 systems Quantized signal levels: Lowest level 16(black) Highest level 35(white) Zero chrominance level SNR peak to peak r.m.s. unweighted (dB) Sample structure Orthogonal, line, field and picture repetitive. R-Y and B-Y samples co-sited with odd (1st, 3rd, 5th, etc.) Y samples in each line spare contacts in the 656 (parallel) interface. A studio standard for GBR component working, rather than the colour difference (Y, Cb, Cr) of the 4:2:2 standard has been proposed. Digital The introduction of the D2-PAL/625 and D2-NTSC/525 digital Green video composite standard into existing or new composite areas has led to equipment operational VTR cassettes, VTRs and computer controlled 'cart' machines. Additionally, equipment for conversion between D1 and