Patent GB-641942-A (GB)
Title: Improvements in or relating to colour television
Inventor: LUBSZYNSKI HANS GERHARD
IPC: H04N9/083
Filed: 1946-12-18
Abstract: 641,942. Colour television. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Dec. 18, 1946, No. 37202. [Class 40 (iii)] [Also in Group XL (a)] In a colour-television transmitting system comprising an electron discharge device in which photo-electrons are liberated by an image of the scene to be transmitted, means are provided for discriminating between electrons of different energies (corresponding to incident light of respective different colours) to produce picture signals representative of the different colour components of the image. First embodiment, Fig. 1. An image of the scene to be transmitted is focused upon the photo-electric cathode 2 of an electron discharge tube. Potentials are applied cyclically to the grid 6 to allow only " blue electrons (i.e. electrons having energies corresponding to liberation by blue light), blue " and " green " electrons, and " blue, " " green " and red " electrons respectively to pass to the target electrode 5 upon which successive electron images are set up. By means of the deflecting coils 11, the electron stream is deflected so that the successive electron images are set up alternately on upper and lower halves of the target electrode. An electron gun 8 scans the two halves of the target alternately, this being so arranged that while the electron image is being set up on one half, the beam from the gun 8 scans the other half. The electron stream returning to the gun 8 is multiplied by the electrode system 9, the output of which comprises a picture signal corresponding to the electron image on the target 5. The tube output is amplified and then applied to a switching circuit which operates in synchronism with the potentials applied to the grid 6. The signals due to the " blue " electrons are switched directly to the transmitting circuits and are also applied to a storage circuit. The second set of signals, i.e. those due to both " blue " and " green " electrons, is applied to the storage circuit in such a manner that it delivers an output corresponding to the " green " electrons only. The second set of signals is applied also to a further storage device to which the third set of signals is later applied to provide an output corresponding to the " red " electrons. The " green " electron and " red " electron outputs are applied to the transmitting circuits in succession to the directly-applied " blue " electron signals. Second embodiment. By suitably controlling the secondary emission from the target 5 and by suitably superimposing different images, the images formed thereon may be made to correspond to the blue, green and red components only. The energy of the electron stream impinging on the target 5 is controlled either by the application of potential pulses to the cathode and grid or by .a further accelerating electrode, by which means the secondary emission may be so increased that a positive charge image is formed on the target 5 instead of a negative charge image. Fig. 4 illustrates the steps in one complete colour cycle. In one half (a) of the blue colour frame a positive image of " blue " electrons is formed on the upper half of the target 5. In the following half-cycle (b) the tube current is cut off. In the first half (c) of the green frame a negative " blue " image is formed and then for the following half-cycle (d) a positive " blue-and-green " image is formed, thus resulting in an overall " green " image. Similarly in the half-cycles (e) and (f) negative " blue-and-green " and positive " blue-green- and-red " images are formed respectively, resulting in an overall positive " red " image. Scanning is effected as in the previous embodi. ment, the electron beam from the gun 8 scanning that half of the target on which the image was laid down in the previous colour cycle. In this embodiment interlaced scanning may be used, the upper charge image being displaced relatively to the lower image by half the line spacing in each image, or the scanning patterns traced on each image being relatively displaced. The scanning lines of each sequence are spaced apart to allow lines of the other sequence to interlace therewith, and in order to discharge the gaps between the lines, the flyback is used, the beam current being increased during the return times by applying pulses to the modulating electrode of the gun 8. The discharge may be assisted by defocussing the beam during the fly-back intervals and by slightly displacing the beam in the vertical direction during these intervals. The signal output is simultaneously suppressed in the amplifying circuits or in the electron multiplier. Third embodiment, Fig. 6. The discharge tube comprises a transparent conducting electrode 22, a photo-electric grid electrode 23 and a further grid 24. By applying in succession suitable potentials to the electrodes 22 and 24 it may be arranged that images of " blue " electrons only, " green " electrons only and '' red " electrons only are formed upon the target 5. The " blue " image is arranged to be on the upper portion of the target, the " green '' image on the central portion, and the " red " image on the lower portion. Specification 626,141, [Group XL (a)], is referred to.