GB1244285A - Improvements in or relating to television systems - Google Patents

Abstract

1,244,285. Television. FERNSEH G.m.b.H. 11 Dec., 1969 [11 Dec., 1968], No. 60593/69. Heading H4F. A PAL video signal A with “ line offset may be separated into substantially pure, whole bandwidth, luminance Y and chrominance Cr signals, despite their overlap in the highfrequency portion of the signal A, by forming the sum (C) and difference (D) of the undelayed signal A and the signal A delayed for one line period (B), delaying the signal D for a further line period (signal E) and linearly combining the signal E with signals C and D. Reliance is placed on the luminance and chrominance contents of each set of three lines being closely similar, and on the fact that the phase of the colour sub-carrier is displaced by 180 degrees every two lines while the phase of the PAL switched component V of the chrominance signal is identical every two lines. The circuit of Fig. 1 thus effectively forms the sum and difference of pairs of lines which are separated by one other line, e.g. the 1st and 3rd lines of a field. In a modification, Fig. 2 (not shown), the Y signal is derived as in Fig. 1, and the Cr signal is formed by adding signals C and D and subtracting 2Y therefrom. In another embodiment, Fig. 4 (not shown), the components U and V of the chrominance signal are derived by subjecting the subcarrier of signal E to a 90 degrees rotation of phase, and forming the same and difference thereof with signal D. In a further embodiment, Fig. 5 (not shown), the signals D and E are synchronously demodulated to give signals proportional to (V - U) and (V + U) which are then matrixed with the Y signal to give colour or colour difference signals. It is also possible to filter out that part of signal A which contains only low-frequency luminance information and to add it to the luminance signal derived from processing the rest of the signal as described above, either directly, or after a one-line delay period, Fig. 6 (not shown). The PAL signal may still be modulated on an I.F. subcarrier, this being advantageous because the delay devices exhibit relatively greater bandwidths at higher frequencies.