| 摘要 |
Either one of the fields of an interlaced television signal is designated as top field as indicated by a first selector signal. The presence of a second selector signal indicates bottom field. A regenerated vertical synchronization signal is furnished for the first horizontal synchronization signal following vertical synchronization in top field. This regenerated vertical synchronization signal resets a counter which counts horizontal synchronization signals repetitively to a count of five. A second regenerated vertical synchronization signal is furnished when the count of five is reached following the vertical synchronization signal of bottom field. The counter is reset by each first regenerated vertical synchronization signal. When a synchronization signal which would normally be designated top field occurs within a predetermined window around horizontal synchronization, the subsequent field is designated top field, i.e. a field switch takes place.
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