New method of producing gradient correlation filters for signal detection.

Coherent optical filtering has been shown to be useful for signal detection.In this type of approach an input signal is crosscorrelated optically with the reference signals; it then appears to resemble most a particular reference signal for which the correlation is maximum. Since similarities between signals often exist, it is sometimes better to correlate the gradients of the input signal and the reference signals rather than to correlate these signals themselves. The correlation of the gradients recognizes the input signal by its perimeter or outline, while the correlation of the signals themselves recognizes it by its area. The gradient correlation is mathematically represented by