GB620137A - Colour television receiving apparatus - Google Patents

Abstract

620,137. Colour filters. SCOPHONY, Ltd. Feb. 21, 1946, No. 5508. Convention date, March 1, 1945. [Class 97 (i.)] [Also in Group XL (b)] In apparatus for producing colour images which includes means for producing successive black and white partial images representative of different colour values (e.g. television or motion picture apparatus), a device is provided for transmitting light the colour of which varies in correspondence with said partial images, said device comprising a pair of light polarising elements having between them a birefringent element and means for applying mechanical strain to said birefringent element to produce the required colour variation. As applied to a colour television receiver, successive black and white colour selection images produced on the fluorescent screen 11 of a cathode-ray tube 10 are viewed through an arrangement comprising two crossed polarizing sheets 12, 13 between which is supported a birefringent sheet 14 in such a manner that currents of different intensities applied to the electromagnet 23 and synchronized with the frame synchronizing signals in the device 26 produce different tensions in the sheet 14 thus producing variation in the colour transmission characteristic of the system 12, 14, 13. The sheet 14 and the tensioning currents may be selected such that the system operates as a three-colour (e.g. red, green, blue) filter, the same colour sequence being used at the transmitter. Instead of applying currents of different intensities to one magnet 23 a number -of magnets, Fig. 4 (not shown), may be employed each being supplied with a current of appropriate strength and suitably switched by electronic means. Alternatively a number of birefringent sheets each associated with a separate magnet may be used, Fig. 5 (not shown). When the birefringent sheet is made from a stiff but elastic material, such as glass, the deformation may be perpendicular to the sheet. This maybe achieved by clamping one edge of the sheet and successively deflecting the opposite edge to different degrees by means of a small cam, having a number of successive rises, and rotated synchronously with the colour frame signals applied to the cathode-ray tube, Fig. 7, (not shown). Alternatively, the perpendicular deflection may be applied by electromagnetic means. It is stated that the invention may be used for motion picture projectors.