Patent GB-1301591-A (GB)
IPC: H04N9/083
Filed: 1970-04-02
Abstract: 1301591 Television HITACHI Ltd 2 April 1970 [4 April 1969 (2)] 15738/70 Heading H4F In a colour television camera requiring only one pick-up tube 22 co-operating with a patterned filter to provide all the necessary chrominance information i.e. a D.C. signal and other signals or distinguishable sub-carries, the filter is arranged so that after every n (positive integer) horizontal scans each sub-carrier is changed in phase by 180 degrees, and the output of the tube is delayed 26 for n horizontal scan periods and added to 24, and subtracted from 25, the undelayed output. The filter may be formed of two tessellated patterns Figs. 5a, 5b, (18, 20 transparent, 19 cyan, 21 yellow) with different horizontal frequencies and the same vertical frequency, or two striped filters, Figs. 6a, 6b, (not shown), and if n = 1, the signals from successive scans l 1 , l 2  may be s (t-h)  and s (t) , Fig. 12. It is known to use a low pass filter to separate the G component, and band pass filters and detectors for the R and B signals, but the bandwidth of the G signal is then less than that obtainable from the tube 22 giving decreased resolution. In the present case the adder 24 provides a D.C. (R+B+2G) signal, and subtractor 25 gives R and B signals on sub-carriers, Fig. 12, which are separated and demodulated at 27-30. A circuit 31 then matrixes the outputs from 24, 29, 30 to give a full bandwidth G signal. Success of the arrangement depends on the degree of correlation between the delayed and undelayed scan signals. To prevent crosstalk between the R and B signals, the R and B components of the incoming image light are caused to follow a different optical path from the G component so that the R and B images are somewhat out of focus and give signals of reduced bandwidth, Fig. 10 (not shown). In Fig. 13 (not shown), two pick-up tubes are used, with a beam splitter, one for the G component and one co-operating with a single striped filter for generating a D.C. blue signal and a red signal on a sub-carrier. In Fig. 14 (not shown) the R and B signals on sub-carriers are obtained by passing the complete signal through respective band pass filters and then subtracting the delayed and undelayed signals, and are matrixed with the complete signal to give G+¢ (R+B). After demodulation the separated R and B signals are matrixed with the G+¢ (R+B) signal to give the G signal. In Fig. 15 (not shown), amplitude limiters placed after the respective band pass filters produce waveforms which are used to switch the D.C. R and B signals i.e. to remodulate them on their subcarriers, and the remodulated signals are subtracted from the complete (R+B+G) signal from tube 22. A uniform white component is added to the image light by a light source and half mirror, so that the signals from the band pass filters include only a small component due to high frequency G information. In these embodiments the vertical resolution; decreased by ¢. Fig. 16 shows an embodiment wherein the low frequency vertical resolution is unaltered, althrough the high frequency resolution is still reduced, the filter 65 serving to remove the modulated R and B components and provide a signal corresponding to differences in G in the compared scans. The circuit of Fig. 17 (not shown) gives the same result, the undelayed and delayed complete signal being added and passed through a high pass filter, and matrixed with R, B signals and the complete signal passed via a low pass filter. The optical image may be stored on film after being passed through the filter, and subsequently scanned, Figs. 18 and 19 (not shown).