Digital Comb-Filter Demodulation of PAL Color-Television Signals

Digital comb filter devices with one or two line memories or with picture memories for the demodulation of PAL color TV signals are presented and compared with respect to their effects on subjective picture quality. The color video signals are assumed to be sampled at four times the color subcarrier frequency, the sampling frequency adopting a definite phase with respect to the color subcarrier. Methods are discussed which are able to stabilize the frame by frame changing of the sampling patterns in the case of comb-filter devices containing only one line memory. It is shown that comb-filters with two line memories and with picture memories have inherent stability and that the decoder with a frame delay guarantees at the expense of a sophisticated hardware full resolution in non-changing parts of a picture sequence.