Patent GB-1426721-A (GB)
Title: Line sequential colour television recording system
IPC: H04N9/81
Filed: 1972-04-19
Abstract: 1426721 Colour television RCA CORPORATION 18 April 1973 [19 April 1972] 18155/72 Heading H4F A composite colour television signal is produced from received red, green and blue signals, by deriving in a matrix a luminance signal and three or four colour signals which are either colour difference signals or sums of colour difference signals, which colour signals are selected in line-sequential form to provide a chrominance signal having nulls at multiples of the line frequency, which chrominance signal is added to the luminance signal, which has maxima at multiples of the line frequency, to derive the composite colour television signal, which may be recorded. The played back composite colour television signal is separated into luminance and chrominance signals using at least two series connected one-line delay lines and associated matrices. In a first embodiment the line sequential chrominance signal is of the form + a, + b, - a, -b, a and b being colour difference signals, the decoder including three series connected oneline delay lines (44, 46, 54, Fig. 2, not shown) the luminance signal being produced by an adder receiving the input composite signal and the signal delayed by two-lines relative thereto, the signals a and b being derived from respective adders each receiving an inverted composite signal and a direct composite signal which is delayed by two lines relative to the respective inverted signal, a commutator being provided so that signals a and b are always delivered to the same respective output terminals.  In further embodiments the line sequential chrominance signal is of the form + a, +b, -(a+b). In one form a=(G-Y), b=0À51 (R-Y), and - (a+b)=0À19 (B-Y), whereas in a further form a=0À493 (B-Y), b=0À877 (R - Y) cos 30 - 0À493 (B-Y) cos 60, and - (a + b) = - 0À877 (R - Y) cos 30 - 0À493 (B - Y) cos 60, i.e. the 0, 120 and 240 degrees NTSC signal vectors. In an encoder for such a chrominance signal, Fig. 6, the luminance signal Y, and colour signals a, b, and - (a + b) are derived by matrix 158, the line sequential chrominance signal being provided by switch 160 and passed to a low-pass filter 162. The chrominance signal output from filter 162 may be added to the luminance signal output of matrix 158 and a colour synchronizing identification burst at 2À0 MHz on the back portion of each "b" line, to derive the composite colour television signal (Fig. 4, not shown). Alternatively the chrominance signal may be passed to a comb filter formed by two one-line delay lines 164, 166 and a matrix 168 to remove any components which are at multiples of the line frequency, the low frequency portion of the luminance signal, separated by low pass filter 170, being passed to a comb filter formed by two one-line delay lines 174, 176 and matrix 178 to remove luminance components which would be separated by the decoder as chrominance components. The resulting comb-filtered low frequency luminance signal portion is added at 184 to the high frequency luminance signal portion from subtractor 172, to derive a luminance signal which is added at 190 to the line sequential chrominance signal to produce the composite colour television signal. The composite signal encoded by the apparatus of Fig. 6, may be decoded by the apparatus of Fig. 3, adder 74 adding the three signals from 76, 78 and 80, to derive the low frequency luminance signal portion, which is added to the high frequency luminance signal portion from high pass filter 68. Each of the colour signals is derived at an output of matrix 84, each output being equal to one of the signals at 76, 78, 80 minus half the sum of the other two of these three signals. The phase of the commutator 86 is controlled by the colour identification burst in each "b" line. In a further embodiment of decoder (Fig. 5, not shown) the luminance signal is derived by subtracting from the input composite signal a fraction of the matrix output which is equal to the signal at 76 minus half the sum of the signals at 78 and 80.