Logical comb filter

Abstract

A logical comb filter comprising a logic decision section for making logical decisions on the selection of signals and a signal generating section for generating signals to be selected according to the logical decisions made by the logic decision section. In the signal generating section, a band pass filter extracts from the input of a composite video signal a signal component centering on a color subcarrier frequency, and a first and a second delay line generate three line signals based on an inverted output downstream of the band pass filter. The inverted output is a main signal. The line signals are apart from one another by one horizontal scanning period. The signal generating section further comprises a first mean level calculator for calculating the mean level between the main signal and a first delay signal obtained as the inverted output downstream of the first delay line, and a second mean level calculator for calculating the mean level between the first delay signal and a second delay signal obtained as the inverted output downstream of the second delay line. One of the output signals and the first delay signal is selected by a changeover switch. In the logical decision section, comparisons are made between the three line signals in terms of level and, if the level of the first delay signal falls between the other two signal levels, the changeover switch selects the first delay signal; otherwise the output signal of the first or second mean level calculator is selected in accordance with the level relationship between the three line signals.