Color image signal processing circuits

Abstract

Circuits are disclosed for processing color encoded video signals, encoded per a format wherein a chrominance signal in the form of a modulated subcarrier is buried in spectrum 'troughs' in the midband of a wider band luminance signal, an illustrative use of the encoding format being in video disc recording. The processing circuits serve, in use with composite signals developed during video disc playback, to convert an input composite signal of buried subcarrier format to an output composite signal of NTSC format. Carrier waves are amplitude modulated in accordance with composite signals developed during video disc playback, and applied to the input of a 1H delay line. Subtractive combination of the modulated carrier waves from both input and output of the delay line effects a first comb filtering action to develop a chrominance signal output in the highband location desired for output use. The delay line output is applied to an amplitude detector. The detected signal is additively combined with the input composite signal to effect a second comb filtering action, developing a luminance signal output free of chrominance components and also lacking vertical detail components. A phase inverted version of the detected signal is also additively combined with the input composite signal to effect a third comb filtering action, and the sum is low pass filtered to provide a vertical detail signal. Combining of the products of the three comb filters provides the output composite signal. The output of the amplitude detector is also used as a substitution signal input to the carrier wave modulator under defect pickup conditions.