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Abstract

A cross-correlation video tracker and method for automatically tracking a relatively moving scene by storing elements from a frame of a video signal to establish a reference frame and comparing elements from a subsequent frame with the stored reference frame to derive signals indicating the direction and angular distance of scene relative movement. A cross-correlation difference signal is generated which represents the difference between a pair of cross-correlation signals dependent on the correlations of the subsequent frame elements and the stored reference elements at two predetermined opposite relative shifts. A circuit is responsive to this difference signal for generating an error signal indicative of the amount of shift required to center the stored reference frame with respect to the subsequent frame. In order to maintain feedback loop stability as the system tracks different scenes which result in varying degrees of decorrelation even with constant shifts in scene position, the circuit responsive to the error signal is also responsive to a gain control signal which represents the difference between a pair of autocorrelation signals dependent upon the correlations of the elements of a representative frame of the video signal at substantially a zero shift and at a fixed predetermined shift. The representative frame of the video signal may be either the subsequent frame or the stored reference frame.

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