GB1457107A - Signal processing - Google Patents

Abstract

1457107 Colour television BRITISH BROADCASTING CORP 30 Dec 1974 [5 Oct 1973] 46705/73 Heading H4F A PAL or NTSC colour television signal in pulse form (e.g. in digital or sampled analogue form at input 30) which has been sampled at a frequency which bears a ratio of small integers to the subcarrier frequency (e.g. three times), is decoded by multiplying 32 the samples of the luminance Y and colour difference signals U and V by coefficients 34 appropriate to each of the Y, U and V signals and to each subcarrier phase position to thereby provide unfiltered output signals Y <SP>+</SP>, U <SP>+</SP> and V <SP>+</SP> which can be reversibly recoded (e.g. at 22, 24 and 26) to form the original input signal substantially without degradation. Considering a PAL signal sampled at three times the subcarrier frequency; the samples comprise P 0 = Y 0 + U 0 ; P 1 = V 1 -¢U 1 -#<SP>3</SP>/ 2 V 1 ; and P 2 = Y 2 - ¢U 2 + #<SP>3</SP>/ 2 V 2 and these are decoded so that Y<SP>+</SP>, U<SP>+</SP> and V<SP>+</SP> at each of the three phase positions are derived in multiplier 32 according to the following matrix The decoding may be used when a coded signal such as a prerecorded signal is mixed 20, or otherwise processed with a studio signal from a local source 10, this signal being filtered 14 and sampled at three times the colour subcarrier frequency in converter 18 before being mixed 20 with the decoded and normalized 36 prerecorded signal, the resulting composite signal then being PAL encoded 22-26. The prerecorded signal may be displayed on a monitor 42 after being decoded 32, 34, D-to-A converted 38 and filtered 40 with a relatively long time constant to average the instaneous outputs. Block decoding may be effected by operating on Y, U and V signals which each comprise the sum of the three successive samples thereof occurring during any subcarrier period. The resulting block samples which are arranged to occur sequentially at thrice subcarrier rate are converted by a register into parallel outputs which are decoded in a manner similar to the first embodiment, but in which only a 3 Î 3 matrix of coefficients is required, before being processed with a local signal (Fig. 2, not shown).