Patent GB-1228626-A (GB)
IPC: H04N11/22
Filed: 1968-09-12
Abstract: 1,228,626. Television signal recording. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 12 Sept., 1968 [15 Sept., 1967], No. 43404/68. Heading H4F. The Specification describes a recording system for recording a television video signal resulting from the normal master scanning of a scene, of the type whereon each line section of the signal is resolved into simultaneous components, e.g. high-frequency and low-frequency or chrominance and luminance and said components recorded sequentially. It is stated that when such a recorded signal is reproduced, interference patterns are seen due to the vertical definition contained in the signals being greater than that reproducable in the final display. To overcome this, the vertical definition contained in at least one of said components is reduced prior to recording. Thus the television signal at the input 5, Fig. 1, of the recording system 7 is separated in 13 into its two components which are supplied to aline sequential switch 19 feeding the recording head 27 and the means 20 for producing said reduction in vertical definition may be operative between the components separator 13 and the sequential switch 19. Alternatively said means can precede the separator, whence both components are adjusted. Such a preceding means is shown in Fig. 2 wherein the video signal is modulated at 39 on to a carrier and the modulated carrier rectified for its negative going half-cycles at 43 and delayed by one line period at 47 and then detected for its positive half-cycles at 58. The modulated carrier formed from the summed outputs of the detectors has a modulation as detected by demodulator 53 corresponding to the average video signal of two consecutive lines. The vertical definition is thereby halved. The Specification refers to the above process as "Electronic spot wobbling". The average of one of the components (e.g. the high frequency) in two consecutive lines may be formed by means 20, Fig. 1, comprising, Fig. 3, a summing circuit 57 fed by the component both directly and via a one-line period delay 59. In the arrangement of Fig. 4 consecutive line averages of both components are formed. Line sequential switch 24 operates in synchronism with switch 19 and the operation of the arrangement is summarized in Table 1. It is seen that the line sequential signal at the output 25 of the switch is formed of component averages grouped in pairs using the same lines. The high and low frequency component separator 13 may be dispensed with in the arrangement of Fig. 5 whence the total video signal (A+B) appears at input 5. Low pass and high pass filters 48 and 50 respectively separate out the component at the inputs to switch 19. The operation is again summarized in a Table 2, the output of the switch 19 (synchronous with switch 54) being the same as in the arrangement of Fig. 4. The arrangement of Fig. 6 is specifically for use in recording colour television signals, wherein the two components are the luminance A and chrominance B signals and the subcarrier of the chrominance signal is of such a frequency (i.e. (n+¢) times the line frequency where n is an integer) that two consecutive line chrominance signals are in phase opposition and their sum is substantially zero, i.e. B r-1 +B r =0. Also consecutive luminance signals are in phase whereby the differences between said signals also approximate to - zero, i.e. A p-1  - A p-2  = 0. Thus in Table 3, summarizing the operating of the arrangement of Fig. 6, the recording outputs at point 25 reduce at respective times T 2 , T 3 , T 4 , T 5 , &c. to (A 1 +A 2 ), (B 1 +B 2 ), (A 3 +A 4 ), (B 3 + B 4 ) &c. The use of separator 13 is thus avoided. Where the television signals have been recorded using any of the arrangement above described a further reduction of interference in the reproduced picture may be produced by employing further delay and combining arrangements in the sequential to simultaneous readout/converter circuits. Thus in the converter arrangement of Fig. 7 the simultaneous signals appearing at inputs 83 and 85 of combining circuit 87 comprise a recorded line component and the average of the said line component and the next but one recorded component of the same type, alternatively. Delays 71 and 73 are each one line period delays and line rate switches 80 and 82 in synchronism. The operation of the arrangement is summarized in Table 4 where the recorded signals C 1 , D 2  &c., may take on any of the forms shown for output 25 in Tables 1 to 3. Figs. 8 and 9 show two further converter arrangements the operation of which are summarized in Tables 5 and 6 respectively. In the arrangement of Fig. 10 the combining circuit 87 is omitted and each recorded signal is spread over two consecutive line periods such that the output at 115 comprises successive pairs of identical combined line signals. Table 7 summarizes the operation of the arrangement. In the arrangement of Fig. 11, the two-output adding circuit 116 has a special function whereby signals C are halved in amplitude when passing through the circuit in the paths 35 to 118 and 111 to 117.'-From Table 8 it is seen that in the combined output at 118 every other line period comprises a component of one type correspond- 'ing to one line, combined with the average of the components of the other type corresponding to the lines surrounding said one line.