Patent GB-714154-A (GB)
Title: Improvements relating to colour television apparatus
Inventor: JAMES IVANHOE JOHN PENFOUND
IPC: H04N9/04
Filed: 1950-12-23
Abstract: 714,154. Colour television. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Dec. 10, 1951 [Dec. 23, 1950], No. 31316/50. Class 40 (3) In colour television apparatus wherein picture signals are generated in such manner that each line of picture signals comprises elements representing different colour components intercalated in a regular sequence, it is arranged that elements representing one colour component or additional signal elements introduced between the colour elements are confined to a separate amplitude range from the remaining element, these separate elements being then employed to separate the colour elements into respective colour channels. In one embodiment, Fig. 1, an image is projected on to the target 6 of a signal-generating tube 1 through a filter 2 formed of a repeating series of blue, green and red strips extending at right angles to the lines scanned on the target. The target is additionally illuminated continuously with a steady blue light from a source 18 having a blue filter 19. The signal appearing across load 11 thereupon takes the form shown. in Fig. 2 in which the blue elements 26 are superimposed on a bias which may be arranged to be somewhat more than, say, + 2 volts. The peak levels of the green and red elements 27, 28 are arranged not to exceed + 2 volts. The signal passes through amplifier 12 and DC. establishing circuit 13 and is applied in parallel to a diode 14 and three gate stages 15, 16 and 17 controlling the input to blue, green and red channels respectively. The diode is biased at its cathode from source 25 to a level of + 2 volts and accordingly becomes conducting only during each blue signal element. The resulting pulses at the cathode are applied to a pulse oscillator 20 and maintain the oscillator precisely in step with the scanning of the colour elements despite any non-linearity in the scanning that may occur. The oscillator controls the opening of gate 15 directly and is applied to open gates 16 and 17 through networks 22, 23 having appropriate delays. The channel signals may be integrated to produce simultaneous trains which may then be employed directly, or utilized to produce frame-, line- or dot-sequential signals. A pulse generator generating successive groups of three pulses may replace oscillator 20 and delay networks 22, 23. The signals set up at the cathode of diode 14 may be passed directly to the blue channel. The signals employed to synchronize oscillator 20 may also be compared with a reference frequency to derive a correcting signal which is employed to linearize the scanning operation. The correcting signal may be generated and stored prior to initiating the generation of image signals and then used repeatedly during the generation of image signals. In another embodiment, colour biasing is dispensed with and the colour filter, Fig. 3 (not shown), is provided with an opaque strip intermediate each group of three coloured strips. The image is projected through the filter in the normal way and in addition continuous illumination is provided from a biasing source of white light. The resulting signal train then takes the form shown in Fig. 4a in which each group of colour elements is followed by a signal 36 extending in a blacker-than-black direction from the black level 35 established by the white biasing light. As an alternative the filter may be illuminated from the rear or the edge with an intensity such that the opaque strips produce signals as shown at 37 in Fig. 4b, extending in the whiter-thanwhite direction. According to another method the opaque strips may be coated at the rear with fluorescent material and irradiated with ultra violet light. With both the signal trains of Fig. 4 the synchronizing pulses are employed to synchronize oscillator 20 as already described, the diode 14 being suitably connected and biased to separate the pulses. A further feature of the invention, Fig. 5, involves the generation of two signals trains, one representing the colour components of the image and generated by means of camera tube 1 operating with a filter 2 as described above and the other representing normal black-and-white detail of the image and generated by camera tube 38. A partially silvered mirror 39 splits the light from the image so as to illuminate both tubes. Filter 2 is of a coarse structure and may have between 70 and 80 groups of strips or less, the colour signal generated being only of low definition. The components are separated as previously described in a circuit 41 and the three colour trains amplified in narrow band amplifiers 42, 43 and 44. The signals are then applied to modulators 46, 47 and 48 where they modulate the black-and-white signal applied from camera tube 38 through amplifier 45. The black-andwhite signal is of high definition as regards picture detail and accordingly each of the colour signals from the modulators, although of low definition as regards picture detail, is caused to be of high definition as regards picture detail. Since only a low definition output is required from camera tube 1 the splitting of the light from the image by mirror 39 may be biased in favour of tube 38. In a modification, amplifier 45 suppresses frequencies in the pass band of amplifiers 42-44, the modulators are dispensed with and the signal from amplifier 45 is added directly to those from amplifiers 42-44. Specification 714,155 is referred to. The Provisional Specification refers to the application of the invention to kinematograph film apparatus of the type described in Specification 475,032.