Patent GB-1270552-A (GB)
Title: Converting equipment of standard color television broadcasting signals
IPC: H04N7/01
Filed: 1969-04-23
Abstract: 1,270,552. Colour television. NIPPON HOSO KYOKAI. 23 April, 1969 [23 May, 1968], No. 20634/69. Heading H4F. Equipment for converting colour television signals from a first colour television standard e.g. 625/50 PAL or SECAM (Trade Mark) signal, to a second colour television standard e.g. 525/60 NTSC signal, comprises (a) a transcoder 3 for converting signals of the first standard e.g. PAL signals, into SECAM type line sequential signals; (b) a luminance-chrominance separator 5 for directing the luminance signal and the chrominance signals to line interpolators 6 and 7 respectively, the luminance signal line interpolator including one and two line period (first standard) delay lines and a weighted adder which includes a switching circuit driven at line frequency for effecting a weighted addition between the one line period delayed luminance signal and the non-delayed luminance signal or two line period delayed luminance signal at such ratios (i.e. 0/1, 1/3, 1/1, 3/1 ,and 1/0) that deviations of the weight positions of the luminance signals in a reproduced picture caused by subsequent line conversion are precompensated, and the chrominance signal line interpolator including one, two and three line period delay lines and a weighted adder which includes a switching circuit driven at line frequency for effecting a weighted addition between the non- delayed and 2 line delayed or between the one and three line delayed signals at such ratios (i.e. 0/1, 1/3, 1/1, 3/1 and 1/0) that deviations of the weight positions of the chrominance signals in a reproduced picture caused by the subsequent line conversion are precompensated (in both line interpolators the signals are preferably frequency modulated on a carrier); (c) an adder stage 8 which produces a line interpolated composite colour television signal of the first colour television standard; (d) a scanning line length difference compensator 9 comprising a plurality of delay lines having delay times equal to integral multiples of a difference in line length between the first and second colour television standards and a switching circuit driven at the line rate of the first standard for compensating the line length differences between the standards; (e) a line converter 10 comprising a plurality of delay lines having delay times equal to integral multiples of the line period of the second standard and a switching circuit operated at the line period of the second standard for converting the number of lines from that of the first to that of the second standard by uniformly deleting lines; (f) a field setter 11 comprising a delay line having a delay of half the line period of the second standard and switching circuit driven at the field period of the first standard for precompensating a deviation of half the line period of the second standard caused by subsequent field conversion so as to retain correct interlacing; (g) a field converter 12 comprising a delay line having a delay time corresponding to the length of the gap formed by the line deletion carried out in the line converter and a switching circuit operated at a period related to the field period of the first standard for converting the number of fields from the first to the second standard by filling the gap having a length equal to the field period of the second standard with a first standard field delayed field signal. The output of field converter 12 comprises almost perfect colour television signals of the 525/60 system for example with the proper sequential disposition of the line-sequential chrominance signals. These signals are further processed by time error compensator 13 for correcting various time errors involved in the signals, and then separated 14 into luminance and chrominance components which are respectively fed to interlace interpolators 15 and 16. Luminance signal interlace interpolator comprises a one line period (second standard) delay line, and a weighted adder which includes a switching circuit operated at the line rate for effecting weighted additions therebetween at such ratios that a periodical vertical jitter for the luminance signal in the reproduced image is compensated. Chrominance signal interlace interpolator comprises a two line period (second standard) delay line and a weighted adder which includes a switching circuit driven at line frequency (second standard) for effecting weighted additions therebetween at such ratios that a periodical jitter for the chrominance signal in the reproduced image is compensated. In the luminance and chrominance signal interlace interpolators the signals are prerfably frequency modulated on a carrier. The outputs of interpolators 15 and 16 are then combined and fed via a field interpolator comprising a delay line having a delay line of one field period plus or minus one half line period (second standard) and weighted adder which includes a switching circuit driven at field rate for effecting a weighted addition so as to compensate for discontinuities of moving objects in the reproduced picture. The resulting signal is then processed 18 and demodulated 19 and passed to transcoder 20 wherein the SECAM type signal is converted into an NTSC signal. In the above arrangement the chrominance subcarrier frequency in the converted signal is slightly different from the standard frequency of the NTSC system. To precompensate for this difference signals of the 625/50 system are recorded in a video type recorder of 625/50 system, and then reproduced by using a tape speed and a head revolving speed based on reference signals corresponding to the synchronizing signals of the NTSC standard colour system including a field repetition frequency of 59À95 Hz and a scanning line frequency of 15,734 Hz. These premodified signals of the 625/50 system from the recorder and then fed to the converter. The reverse conversion from the 525/60 system may be effected by passing the signals through the converter in a sequence contrary to the above forward conversion. The specification explains how using the present converter a 525/60 NTSC signal can be converted into a 625/50 PAL signal with “ line offset without using a videotape recorder i.e. on a real time basis.