GB843490A - Improvements relating to derivation of colour television signals - Google Patents

Abstract

843,490. Colour television. ELECTRIC & MUSICAL INDUSTRIES Ltd. Sept. 27, 1956 [Sept. 29, 1955], No. 27686/55. Class 40(3). Relates to methods of generating colour television signals in which signals corresponding to one colour or colour mixture are produced with relatively high definition and signals corresponding to another colour or colour mixture are produced with relatively low definition. According to one aspect of the invention, Fig. 1, equal area images corresponding to the red (R), luminance (Y) and blue (B) components of an object are formed side-by-side on a film 1, and are scanned by a flying-spot scanner 2 to generate signals in a photo-cell 5 in the normal manner except that the line scan generator 3 is controlled to produce a waveform as shown in Fig. 4 comprising three different slopes, whereby the resulting component signals differ in definition, the luminance component being of greatest definition and the blue component of least definition. In an alternative arrangement, the three images may be arranged in a vertical array and the frame scan controlled so that a different number of lines in accordance with the definition required occupies each image. The signals from photo-cell 5 pass to a transmitter 6 and thence via a cable 7 to a receiver 8 associated with three cathode-ray tubes 9, 10, and 11, the scanning of which is controlled so that each displays only one of the component images. According to another aspect of the invention, the areas occupied by the three images are arranged to be suitably different and the scanning velocity is maintained constant. This is illustrated in Fig. 2 where fieldsequential red, luminance and blue signals from a camera 1 are gated successively from an amplifier 2 by means of gates 6, 7 and 8 to three display cathode-ray tubes 3, 4 and 5. The resulting images are then projected on to the target 13 of a pick-up tube 9 by three lens systems 10, 11 and 12 in the manner shown so that the ratio of the width of the luminance image to the width of the red image and ratio of the depth of the blue image to the depth of the luminance image are according to the definitions required, the three images being scanned as one image in the normal manner at uniform velocity. Reference is made to an alternative arrangement in which the positions of the red and blue images are transposed, and also to an arrangement in which the three images are disposed in a vertical array with different depths. A film for scanning by a flying-spot-scanner may also be prepared with the three images disposed as shown in Fig. 2. Signals derived from vertical or horizontal arrays of images are compatible inasmuch as by increasing the scan amplitude in a monochrome receiver to which the signals are applied, it can be arranged that only the luminance image is visible on the screen. The invention is stated to be of application in systems for converting from sequential to simultaneous signals, Specification 778,179 being referred to in this respect. Signals produced by the invention are also of relatively little extra bandwidth compared with monochrome signals and are of use in relay systems.