Separation circuit using adaptive comb filter for separating luminance

Abstract

A separation circuit for separating luminance and color difference signals in a composite color signal has first and second 1H-delay circuits delaying the input signal. First, second and third bandpass filters respectively filter the input, 1H-delayed and 2H-delayed color signals, the output of the second bandpass filter being inverted. A first adder circuit provides the arithmetic mean of the first and third bandpass filter outputs at a level a to a differential amplifier to which is applied the inverted signal at a level b from the second bandpass filter. The differential amplifier outputs a signal having a level (b-a)k+b, where k is a constant. A middle level output circuit outputs the middle level signal from among the outputs of the first and third bandpass filters and differential amplifiers. A second adder circuit outputs the arithmetic mean of the middle level signal and inverted signal from the second bandpass filter as the separated color difference signal. The output from the first delay circuit is also passed through a further delay circuit and supplied to a third adder circuit where the arithmetic mean of this signal and the ouptut from the second adder circuit yields the separated luminance signal. In one embodiment, the second bandpass filter is replaced by a bandpass filter group having a bandpass stage and a band-elimination stage with complementary characteristics. A further adder circuit receives the signal from the bandpass stage and the middle level signal and supplies the arithmetic mean thereof to the third adder circuit which also receives the band-eliminated signal and provides the arithmetic mean therefrom as the separated luminance signal.