Television apparatus

985,622. Colour television. INTERNATIONAL POLAROID CORPORATION. July 6, 1961, No. 24528/61. Heading H4F. A colour television system is based on the " red-white " theory of colour reproduction disclosed in article " An Astonishing New Theory of Colour," by F. Bello in Fortune, May, 1959. The original image is analysed in terms of relatively long and relatively short visible wavelength light to produce corresponding electrical signals and is reproduced by means of cathode-ray tube light-emitting elements which produce red and minus red (i.e. white minus red) light, the method of operation being such that the relatively long wavelength image is reproduced in red light and the relatively short wavelength image is reproduced in achromatic (i.e. white) light. In a first way of carrying out the invention the original image is analysed by means of red and green filters (specifically a filter which is opaque to wavelengths less than 580 mÁ and a filter which transmits in the band 480-600 mÁ), the " red " signal is applied to control the red light-emitting elements whilst the " green " signal is applied to control both the red and minus red light-emitting elements so as to produce white light. In a second way of carrying out the invention the red filter is replaced by a yellow (i.e. red plus green) filter (specifically a filter opaque to radiation less than 510 mÁ), so that the " red " signal contains information about the green components of the image, and the " red " and " green " signals control the red and minus red lightemitting individually without the need for the dual control by the " green " signal which is employed in the first method. In effect the electrical cross-connection at the receiver in the first method is replaced by an optical crosscoupling at the transmitter in the second. The transmitter may employ two orthicon cameras in association with a half silvered mirror and filter or a dichroic mirror. The receiver may employ a shadow-mask type of cathode-ray tube with suitably selected phosphors, although reference is made generally to other arrangement. Transmission may be physical circuits, e.g. coaxial cable, or by radio waves. Reference is made to the use of the N.T.S.C. system of colour television with two of the three colour components selected in accordance with the principles of the invention.