Scan converter for a high definition television system

Abstract

A high definition B-MAC television signal transmission system comprises a scan converter and a signal pre-processor for accepting signals in various high definition formats. In particular, an 1125 line or 1050 line to 525 line scan converter is required due to the preponderance of at least 1125 line and to some extent 1050 line 60 Hertz field rate format high definition television studio equipment. The scan converter includes circuitry for converting from horizontal to vertical scan format via first and second field stores. A phase shift transversal filter spatially shifts every sample of each field by 1/4 line. In alternate fields, the direction of spatial shifting reverses. For an interlace output, alternate line samples are discarded or for a sequential scan output, all samples are used. The output of the transversal filter is scan converted to reassume a horizontal scan format. Three field stores are used to buffer the input and output fields rates such that one field of samples is dropped every one thousand fields in order to convert from a 60 Hz field rate to 59.94 Hz. At the same time, the coefficients of the transversal filter are reversed for the next field of samples after the dropped field. The scan converter provides a digital 525 line 1:2 or, in another embodiment with two field rate converter circuits, a 1:1 format output. According to B-MAC signal processing, an interlace 525 line output is provided to a pre-processor which additionally may accept a 525 line analog RGB input. Also, the pre-processor may generate its own test pattern signals.