Patent GB-1008111-A (GB)
Title: Apparatus and process relating to television
Inventor: SPOONER ARCHER MICHAEL
IPC: H04N7/01
Filed: 1961-11-10
Abstract: 1,008,111. Television. REDIFFUSION TELEVISION Ltd. Jan. 10, 1963 [Nov. 10 1961], No. 40343/61. Heading H4F. The invention relates to apparatus for converting television signals of a first scanning standard (or a carrier modulated by such signals) into signals of a second scanning standard employing a plurality of charge storage devices 1, 2, 3 which are employed in sequence to record the input signals under the control of line and field scan generators L1, F1 operating at the first standard and from which output signals are derived in sequence under the control of line and field scan generators L2, F2 operating at the second standard, an electric control circuit (not illustrated) which responds to pulses at the first and second field rates, being employed to effect switching operations throughout the apparatus at the appropriate times such that information in any storage device is completely read before a subsequent writing is made. In accordance with the invention the control circuit operates so as to allow for departures (due to drifting) from the correct nominal relationships between the field ratio of the two standards by omitting or effecting an extra writing operation. Thus, in the case where the two field ratios are equal, writings, each comprised of a pair of interland fields, take place in devices 1-3 in repeating sequence and read-out follows in like sequence with the writing and reading operations timed so as not to overlap in any device. However, if the field rates drift so that the read-out operations tend to catch up with the writing operations overlap will recur. This is prevented by repeating a writing operation by causing a field written in one device also to be written in the next device in the sequence. Similarly, if the field frequencies drift so that the writing runs too fast a writing field is omitted. In the case where the field rates differ such that the output field frequency is less than the input field frequency the reading operations are regularly jumped in the sequence to allow for the difference and where the output field frequency is higher than that of the input a writing operation is regularly repeated in a following device. The invention operates in such circumstances when drift occurs to omit or insert an extra writing which would otherwise not take place. The invention may be applied to: (1) the conversion of line frequency where field frequency is unchanged but subject to drift; (2) the conversion of both line and field frequencies; (3) a system for relaying signals without change of fundamental standards but where drift may occur in the field frequencies employed at the terminals of the system; (4) a system for converting signals derived from kinematograph films operating at 24 frame per second into signals at 25 frames per second television standards. The storage devices may comprise single or double-gun cathode-ray storage tubes, cathode-ray image display tubes having short screen persistence and operated in conjunction with storage-type camera tubes for read-out, or similar arrangements in which the visible display is stimulated by a uniform field. If the read-out operation does not completely erase stored information, provision is made to include erasing signals in the sequence of operations. Reference is made (without giving details) to a method of operation in which only one interlaced field is covered in each storage device. Detailed waveforms illustrating the operation of the invention are given for both conversion with and without change of field frequency, Figs. 2-5 (not shown).