GB749511A - Improvements relating to colour television apparatus - Google Patents

Abstract

749,511. Colour television. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Dec. 22, 1953 [Jan. 2, 1953], No. 98/53. Class 40 (3). An image is projected simultaneously on to two pick-up tubes 1 and 2, the first of which operates in conjunction with a filter 9 'to generate a signal Ey representative of the luminance of the image, and the second of which operates in conjunction with a blue and red striped filter 7 to generate intercalated signal elements representative of the red and blue colour components of the image. Filter 7, Fig. 2, comprises vertical blue and red translucent stripes 7b, 7c interleaved with opaque indexing stripes 7a. A source of white light 8 illuminates the pick-up tube through the filter and causes the colour signal elements to be elevated above the true black level whereby the output of the tube corresponding to the opaque stripes corresponds to blacker-than-black pulses. The output of tube 2 is applied to two gates 13, 14 and a limiter stage 12 which separates out the blacker-than-black indexing pulses and applies them through networks 15 and 16 of appropriate delay to cause gates 13 and 14 to be opened at the instants of receiving the blue and red signal elements. The outputs from the two gates are then smoothed to derive continuous blue and red signal trains Eb and Er. The signals Ey, Eb and Er are combined to generate a composite signal, Fig. 3 (not shown), illustrating schematically an arrangement for producing a signal of the form where # is the angular velocity of a sub-carrier signal. The Eb and Er signals need only have a relatively low definition, of the order of 2 Mc/s. or less, and therefore the stripes of filter 7 are made correspondingly wide. As an alternative to opaque indexing stripes, filter 7 may have clear stripes and operate in conjunction with a biasing light arranged to produce whiter-thanwhite pulses. Reference is also made to the use of the tube described in Specification 743,156, having a special construction of target electrode. The scanning linearity of tubes 1 and 2 can be maintained by comparing the indexing pulses in the output of tube 2 with a constant frequency oscillation and employing any difference to correct the scanning wave forms. Specification 714,154 also is referred to.