An adaptive filtering system is disclosed, which may be used in a digital television receiver to extract low frequency vertical detail information from a comb filtered chrominance signal. This system provides wide bandwidth vertical detail information when the amplitude of the chrominance component of the composite video signal is low and narrower bandwidth vertical detail signals as the amplitude of the chrominance component increases. Adaptive filtering is accomplished by passing the comb filtered chrominance signal through a first low-pass filter (14) and developing two reduced amplitude replicas (21,21) of the filtered signal which are mutually supplementary. The ratio of the amplitudes of these two replicas is variable with a control signal.
One replica is passed through a second low-pass filter (22) and combined (26) with the other replica to produce a vertical detail signal. The embodiment of the system that is disclosed includes means (41-46) for developing a control signal that is dependent on the instantaneous amplitude of the chrominance component of the composite video signal.