Patent GB-631095-A (GB)
Title: Improvements in and relating to television, photo-copying and like processes
IPC: H04N9/11
Filed: 1945-04-18
Abstract: 631,095. Copying by scanning. GENERAL ELECTRIC CO., Ltd., and JESTY, L. C. April 18, 1945, No. 9757. [Class 40 (iii)] In a television &c system in which a picture (films &c.) is scanned by a light beam to produce a copy image, or to generate television signals, means are provided for varying the intensity of the light beam automatically in accordance with changes in a characteristic of the picture. An application of the invention to the production of copy images of colour cinematograph film is shown in Fig. 2 in which a scanning light spot produced by a cathode-ray tube 10 scans a colour film 13A the light transmitted through the film being directed via a lens system 14 and rotating three-sector colour filter 16, on to a negative 15A driven synchronously with film 13A by means of motor 28. Part of the light beam between lens 14 and filter 16 is split up into three subsidiary light paths which are directed by means of small mirrors 18 on to three photoelectric cells through separate subsidiary colour filters (one of each of which is shown at 20 and 19 respectively) and the signals generated by each cell 20 are applied to separate amplifiers (one of which is shown at 21) three separate magnitudes of output from each of which, developed across potential divider 32 (in the case of amplifier 21), are applied, recurrently by means of cam-operated switches 35 to the input of a logarithmic (or arithmetic) combining circuit 22 the output from which is fed to intensity control electrodes of the cathoderay tube 10. The magnitudes of the separate outputs from each of the amplifiers 21 and the cam switching sequence are arranged such that the output of the amplifier which is associated with a filter 19 of the same colour as the operative sector of filter 16 is applied via 22 to the intensity control electrode so as to increase the intensity of the scanning beam whilst, simultaneously, the outputs from the other two amplifiers are combined, in suitable proportions, in unit 22 so as to oppose this increase. In this manner the intensity of each colour in the picture is reduced in accordance with the intensity of the other two colours, these latter colours acting as masking colours. A modification for the production of " stills " is described with reference to Fig. 1 (not shown). By substituting a photo-electric cell having a suitable colour response for the negatives in the above embodiments television signals may be obtained for transmission, or for recording, by employing a second cathode-ray tube operated synchronously with the transmitter cathode-ray tube. According to the Provisional Specification, instead of using three subsidiary light paths a single subsidiary path may be employed with one photo-electric cell and a three-section variable colour filter, the settings of the amplifiers being varied according to the colour filter in use. Also according to the Provisional Specification by omitting the colour filters and employing a single subsidiary light path and associated photo-electric cell and amplifier, the arrangement may be used for copying in monochrome.