GB1025512A - Television standards conversion - Google Patents

Abstract

1,025,512. Television line standards converter. BRITISH BROADCASTING CORPORATION. Oct. 5, 1964 [July 5, 1963; March 6, 1964], Nos. 26838/63 and 9703/64. Heading H4F. The invention relates to a television line standards converter of the type described in Specification 928,730, in which there is provided a plurality of storage elements 47 in association with switch means 41 and 42, Fig. 8, operating respectively at the input and output line rates, and is concerned with eliminating a defect which is due to the simultaneous engagement of a storage element by both switches once in each beat cycle of the difference between the input and output line frequencies. Fig. 2 illustrates the problem when converting from a higher to a lower line frequency (specifically 625 to 405 lines per picture interval) where simultaneous engagement occurs during a sequence including input lines 3, 5, 7, 10 &c. In accordance with the invention the drive 58 for switch 41 is controlled by a switching circuit 57 which is controlled by input and output line synchronizing pulses and functions to interrupt the drive during the lines when simultaneous engagement may occur. The storage elements are in the form of capacitors 47 and use is made of an interpolation system 49, 50, 51, 64, 65 as described in Specification 966,318 whereby the signal applied to the storage elements are formed by combining proportions of the signals from adjacent field lines. However, in contrast to Specification 966,318 where the proportion varies throughout a line period, so as to allow for the inclination of the output lines with respect to the input lines, the present invention uses constant proportions thereby causing the output signal to represent information due to a virtual raster, Fig. 2, formed of lines 1<SP>11</SP>, 2<SP>11</SP>, 3<SP>11</SP> &c. which are parallel to those of the input signal raster. The interpolation system is controlled by a function generator 56 producing a signal of the form described in Specification 966,318. The signal is applied to the interpolation system via a sampler 62 and pulse lengthener 63 by means of which the appropriate value of the function for a particular line is chosen and then held constant throughout the line. The sampler is operated by switching circuit 57. Apparatus for converting from a lower to a higher line frequency, Fig. 11 (not shown), is generally similar to Fig. 8 but the input switch 41 operates continuously whilst the operation of output switch 42 is interrupted by switching circuit 57. The interpolation system operates on the output signal and involves the use of a more complex delay system which provides delays of one, two or three lines, Figs. 6 and 12-18 (not shown), since the signal from switch 42 is not continuous due to the interruptions by circuit 57. Use may be made of the interpolation system described in Specification 1,019,811 where interpolation is made between adjacent lines of a picture as distinct from those of an interlaced field. The arrangement is described with reference to Figs. 20-27 (not shown) and involves the use of delays of one field plus one half line so as to bring signals due to adjacent picture lines into time coincidence. A suitable arrangement for circuit 57 is described (in block diagram form only) with reference to Fig. 10 (not shown).