GB1368946A - Colour television camera arrangements - Google Patents

Abstract

1368946 Colour television EMI Ltd 9 Nov 1971 [10 Nov 1970] 53360/70 Heading H4F A colour television camera is provided with a source of bias light 5 and a filter 6 for producing a signal in the output of tube 4 indicative of the position of the scanning electron beam of tube 4. This may be used to register the scanning of the red, green and blue images on the tubes of a three-tube colour television camera or may be used to register the scanning beam of a one (or two)-tube line sequential colour television camera. In this latter case a horizontally (for a horizontal line scan of tube 4) striped colour filter 2 is focused on to the target of tube 4 and filter 6 superimposes on this pattern vertical red, green and blue stripes of different repetition frequencies. The output from tube 4 contains a superimposed signal indicative of the coloured stripe being scanned as each stripe of coloured light passed by filter 2 has superimposed on it a different frequency due to filter 6. This superimposed signal may be used to cause accurate scanning of one coloured stripe, or, if scanning is not accurate, it may cause the appropriate amounts of the undesired signals, which have been stored from previous lines, to be subtracted from the resultant signal. Instead of scanning each stripe separately, tube 4 may be arranged to scan a pair of stripes at each line scan, the red, green, and blue signals being derived by matrixing. For a three-tube camera filter 6 is monochrome and has lines of different frequency markings so that the line being scanned is identified by the superimposed frequency, and the position in the line is identified by the phase of the superimposed signal. To eliminate picture information at the repetition frequencies of the stripes of filter 6, the picture image may be de-focussed, or two overlapping picture images may be formed, with a separation equal to half the pitch of the red stripes of filter 6.