Patent GB-891941-A (GB)
Title: Improvements relating to pick-up devices for colour television
Inventor: WATSON GEORGE ROSS
IPC: H04N9/07
Filed: 1957-04-11
Abstract: 891,941. Television. ELECTRIC & MUSICAL INDUSTRIES Ltd. April 3, 1958 [April 11, 1957], No. 11872/57. Class 40(3). In a colour television signal generating arrangement an image of the scene is directed on to the target of a single pick-up tube 4 (Fig. 1) via a rotating colour filter 2 (alternate segments of which, as shown in Fig. 6, transmit green light and intervening segments of which transmit red and blue light) and a fixed line filter 3 (consisting of fully transmitting strips separated by strips passing green and red light) the output signals from the tube which consist of green signals in alternate fields and red and blue signals in intervening fields, the blue signals occuring as modulations of a carrier wave the frequency of which is determined by the "pitch" of the strips in filter 3, being supplied directly and via a storage device 7 in alternate and intervening fields respectively to a green signal output line 6 and directly and via a storage device 12 in intervening and alternate fields respectively to a low-pass filter 8 which selects the red video signals and to a demodulator 11 which recovers the blue signals. In this manner simultaneous colour television signals are generated by a single camera tube thus avoiding registration errors and the need to correct for sensitivity variations which occur in cameras employing three pick-up tubes. In a modification of this arrangement the tube ouput is supplied directly to the low-pass filter 8 and the demodulator 10 (during intervening fields) the outputs from which are then supplied directly and via individual storage devices to the respective output lines 9 and 11 whilst the green channel is operated as already described (Fig. 2, not shown). In a second embodiment (Fig. 3) the pick-up tube 4 is provided with two interleaved comb-like signal electrodes (4a, 4b, Fig. 7) alternate strips of which are associated with filter elements passing red and green light and intervening strips of which are associated with filter elements passing blue and green light. The output from each electrode is supplied via respective amplifiers 15, 16, firstly, to an adding circuit 17 the output from which is supplied via switch S4 during alternate fields (i.e. those fields which occur when the green segments of filters 2 are operative) to a. storage device 7 and, via switch S2, to the green output line 6 and, secondly, during intervening fields to respective storage devices 13, 14 and, via switch S2, to the red and blue output lines 9 and 11 respectively. During the latter fields (i.e. those fields which occur when the red plus blue segments of filter 2 are operative) green signals are supplied to the output line 6 from store 7 via switch 2 whilst, during the alternate fields, the red and blue output lines 9, 11 are supplied, via switch S2, from their respective stores 13, 14. Fig. 4 shows a modification of the latter embodiment in which a single storage device 20 only is required for the red and blue signals. In this arrangement the outputs of amplifiers 15, 16 are combined in opposite polarities in adder 19 (the output of 15 being inverted in 18 for this purpose) and supplied to the store 20 from which via a separator stage 21 and switch S2, the red and blue signals are supplied to their respective output lines 9, 11 during the intervening field periods. When a "Y" luminance signal is required instead of the green signal, two alternative operative optical paths to the pick-up tube are provided, one containing a "Y" filter and the other a strip filter of the kind employed in the embodiments of Fig. 1 or Figs. 3 and 4. In an alternative arrangement, applicable to the embodiments of Figs. 1 and 2, the green filter segments are replaced by a filter transmitting 0.59G + 0.30R and a blue signal (0.11B), derived from output line 11, added thereto. In all of the embodiments the storage devices may comprise cathode-ray tubes, magnetic tape or drum arrangements or sonic delay lines. Reference is made to the application of the invention to colour film scanning arrangements in which each film frame is imaged on the pick-up tube for a plurality of field periods to reduce colour fringing effects. Specification 657,666 is referred to.