Patent GB-1191117-A (GB)
Title: Improvements in Film Scanning Systems
IPC: H04N3/38
Filed: 1967-06-23
Abstract: 1,191,117. Television. COMPAGNIE FRANCAISE THOMSON HOUSTON-HOTCHKISS BRANDT. 23 June, 1967 [24 June, 1966; 28 June, 1966], No. 29222/67. Heading H4F. Specification describes a double beam interlacing telecine system of the type comprising a flying spot scanning tube T1, a support for the film F to be scanned including a pair of abutting scanning windows F1 and F2, each half a film frame height in height, a pair of lenses L1 and L2 each focusing the scanning frame on the scanning tube on to a respective one of said scanning windows in the plane of the film, a shutter O, located close to the film support and alternately obturating one of the two light beams arriving at the scanning windows, a light condenser C and a photo multiplier Ph, wherein, so that scanning rasters of different aspect ratio (height) may be used without necessitating corresponding change of the shutter speed, said shutter moves with a linear obturation speed so selected as to be intermediate the extremes of linear speeds respectively necessary for the synchronous obturation of the different scanning rasters to be used, the greater the difference in aspect ratios of said scanning rasters, the greater being the height of the opaque portions of the shutter. One use of scanning rasters with different aspect ratios exemplified is when a first film to be scanned is of standard aspect ratio, i.e. 3/4 and is reproduced with the same standard and the second film to be scanned is of the " cinemascope " type bearing an anamorphically distorted image in a nearly square frame which is reproduced, after height compression, as an undistorted image in a frame of aspect ratio 1/2À35. In the first case the scanning raster has an aspect ratio 3/8, the lenses L1 and L2 inverting the raster whereby at the film the scanning spot moves up the film against the movement of the film and the raster, relative to the film, has the aspect ratio 3/4. In the second case the scanning raster has an aspect ratio obtained by reducing the horizontal scanning by the ratio 0À88 and increasing the vertical scanning by the ratio 1À75, giving 5À25/7À04. This raster extends beyond the windows F1 and F2 at the top and bottom, whereby, when the film is reproduced by a standard 3/4 raster, the film image is " compressed " in height, with approximately 30% of the top and bottom of the frame carrying no image. Two rasters are simultaneously present at the two windows F1 and F2 and it is the purpose of the shutter O to obscure each of these rasters in turn. The opaque part of the shutter thus has to move upwards whereby the scanning spot of the raster to be obscured always falls on said part. In Fig. 3 is shown, slotted against time t, the height position within the two windows F1 and F2 of the scanning spot for the standard scan S and the cinemascope scan C, over a period of two successive interlaced scans of the same film frame. In the first scan, the scanning spots (dotted lines) at the lower window F2 are to be obscured and in the second scan, the upper wider scanning spots are to be obscured. One shutter to produce this obscuring for both types of scan S and C must have an opaque portion of height between m and M. The best choice is the average of these extremes whereby the opaque and transparent portions of the shutter have equal heights. The speed of the shutter is then ideally (1 + 1À75)/2 = 1À375 times the speed for the synchronous obturation of the standard scanning spot.