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Abstract

A digital comb filter for decoding composite video signals into a luminance and a chrominance component. A Fast Fourier Transform (FFT) circuit or a band split filter circuit is used to determine important characteristics of an input video signal without demodulating the video signal. The circuits produce a signature signal by which each of the video lines can be correlated. Signature signals on various surrounding video lines that are of opposite subcarrier phase with the current line are compared to determine similarity and appropriate weighting coefficients for the surrounding lines. If none of the surrounding lines are similar, the comb reverts to a band split filter to form chrominance. A noise measure circuit determines an error signal input used to adjust the weighting coefficients as the noise level increases or decreases. Multiplexer combines high pass and low pass taps of a band split filter into a single data stream. Line delays, together with field delay memories, provide the interlaced line above and below the current line. for the comb filter. Interframe motion detector gives priority to the frame comb signal when no motion is detected between the current line and the frame delayed signal in the same vertical position as the current line. Dynamic threshold modification is used to suppress unwarranted comb filter failures in the presence of luma edges.

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First Claim