Patent GB-1445896-A (GB)
Title: Colour television camera
IPC: H04N11/22
Filed: 1973-12-31
Abstract: 1445896 Colour television cameras PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 31 Dec 1973 [24 Jan 1973] 60310/73 Heading H4F A colour television camera provided with coloured filters on a rotating filter wheel CF (or a moving endless filter strip, Figs. 4, 5, not shown) and a pick-up device PD having a number of read strips D 1 , D 2 , D 3  has outputs PD 1 , PD 2 , PD 3  at which are simultaneously developed sequential signals by the simultaneous reading of the read strips D 1 , D 2 , D 3 , the time taken by each of the coloured filters of filter wheel CF to move the width of one read strip D being equal to the time taken to read that strip; the signals from outputs PD 1 , PD 2  and PD 3  are supplied to a converter including switches SY, SR, SB and delay circuits TR and TB to derive at outputs QY, QR, QB simultaneous signals representing different colours but being derived, at any instant, from the same read strip. The pick-up device PD may be formed with a plurality of photo-transistors or photodiodes; alternatively a pick-up tube having at least three electron beams may be used. In the embodiment shown in Fig. 1 the filters are transparent (Y) red (R) and blue (B), each filter moving the width of the three read strips D 1 , D 2 , D 3  in one television field period; the resulting signals at PD 1 , PD 2 , PD 3  are thirdfield sequential, the switches SY, SR, SB being switched three times each field and the delay circuits TR and TB having delay times of onethird and two-thirds of a television field period respectively. To provide pseudo-interlaced signals certain of the readings of each read strip may be timedisplaced by half a line period relative to the other readings; actually interlaced signals may be developed by interlaced scanning of the pick-up device PD. To provide interlaced signals when the three read strips D 1 , D 2 , D 3  are read in an identical manner additional halfline delays (TR1, TB1, Fig. 2, not shown) and switches (SR1, SB1) are included between delay circuits TR, TB and respective output terminals QR, QB to ensure that the red and blue output signals are correctly interlaced with the luminance output signal, output QR being connected directly to delay circuit TR for two-thirds of each field and being connected to delay circuit TR via the half-line delay (TR1) for one-third of each field, output QB being connected directly to delay circuit TB for one-third of each field and being connected to delay circuit TB via the half-line delay (TB1) for two-thirds of each field. In another embodiment (Fig. 3, not shown) in which the transparent filters (Y) are replaced by green filters (G) delay circuits TR, TB are omitted, the "green" switch SG receiving inputs directly from outputs PD 1 , PD 2 , PD 3 , the switch SR receiving signals from outputs PD 1 , PD 2 , PD 3  which have been delayed by one-third of a field and the switch SB receiving signals from outputs PD 1 , PD 2 , PD 3  which have been delayed by two-thirds of a field. In a further embodiment (Fig. 4, not shown) transparent (Y), green (G), red (R) and blue (B) filters are provided in combination with four read strips D, four switches (SY2, SG2, SR2, SB2) switched four times each field, respective delay circuits of delay times one-quarter of a field, one-half of a field, and three-quarters of a field being provided between the "colour" switches (SG2, SR2, SB2) and the output terminals. In a further embodiment (Fig. 5, not shown) transparent (Y), blue (B), transparent (Y) and red (R) filters are provided in combination with two read strips D, and three switches (SY3, SR3, SB3) switched twice each field. The output from each of the "colour" switches (SR3 or SB3) is fed to a half-field delay (TR6 or TB6) and then directly and via a one-field delay (TR7 or TB7) to a switch SR4 or SB4) operated at field frequency to provide a respective continuous signal (R or B). Alternatively this embodiment may be adapted for three read strips D and filters which are transparent (Y), blue (B), green (G) transparent (Y), red (R) and green (G). Mechanically moved filters may be replaced by a liquid colour filter providing moving filter strips. Light fibres may be provided for directing the light from the filters to the read strips.