Patent GB-898523-A (GB)
Title: Improvements relating to the generation of colour television signals
Inventor: PERKINS DENIS GORDON
IPC: H04N9/07
Filed: 1957-09-19
Abstract: 898,523. Television. ELECTRIC & MUSICAL INDUSTRIES Ltd. Sept. 19, 1958 [Sept. 19, 1957], No. 29461/57. Addition to 852,506. Class 40(3). In a colour television system of the kind described in the parent Specification in which a first colour component is stored in a line pattern on the target electrode of a pick-up tube during alternate field periods and a second colour component stored in a line pattern during intervening field periods whilst a third colour component is stored without a line pattern during all field periods, means are provided responsive to differences between the signal output of the tube during successive field periods for separating signals representing the individual colour components. As shown in Fig. 1, the output of the pick-up tube 1 is supplied to a storage tube 4 of the kind described in Specification 893,951 the storage electrode of which is positively charged by a light stimulus during the blanking intervals so that during successive scans of this electrode the output signals consist of the difference between the signals currently "laiddown" and the signals "laid-down" during the preceding field scan together with a constant signal due to the light stimulus. In the present arrangement the signals stored in pick-up tube 1 in line patterns are the blue and red colour components whilst the green component is stored without such pattern. The output of the storage tube 4 thus consists of interleaved red and blue representative pulses of opposite polarity respectively with respect to the constant light stimulus signal and the polarity of which reverses during successive field scans. Since the green component signals are substantially the same during successive fields cancellation of these signals results. The output of tube 4 is then supplied to a separator stage 5 which separates the red and blue signals on a polarity basis and supplies the blue signals via switch 7 to terminal 6 and the red signals via switch 10 to terminal 8 the polarity inverter 9 and the switches which change over at the field scanning rate of tubes 1 and 4, serving to ensure that positive pulses of the appropriate colour are always supplied to terminals 7 and 8. In order to derive green representative signals the negatively going output from 5 is combined with the total output signals from tube 1 in adder 11 the output from which is the required green signal. Fig. 3 shows a second embodiment in which to reduce colour shading and field frequency flicker caused by variations in sensitivity of the storage device two storage tube devices 19, 22 similar to 4 of Fig. 1 are employed. In operation the output signals from tube 1 during successive fields are supplied alternately via switch 18 to the two devices 19, 22 which during the intermediate fields (when no signals are being "laid-down") are scanned by an unmodulated electron beam to "read" the stored signals and supply such to the inverter 20 and adder 21, each device, at the end of its "reading-out" scan only, receiving a reference light stimulus as described in connection with device 4 of Fig. 1. Since the output signals of the storage devices during the "laying-down" scan are not utilized the spurious signals in the latter have no effect. The output signals from adder 21 are then supplied to the separator stage 5 as described in connection with the embodiment of Fig. 1. An alternative arrangement replacing the rotating colour filter disc 2 and the strip filter 3 of Fig. 1 employing a rotating mirror disc, two plane mirrors and two strip filters is described in connection with Fig. 2 (not shown).