4.38 Consider the two-dimensional linear filter given as the output (4.154).

(a) Express the two-dimensional autocovariance function of the output, say, γy(h1, h2), in terms of an infinite sum involving the autocovariance function of xs and the filter coefficients as1,s2 .

(b) Use the expression derived in (a), combined with (4.153) and (4.156)

to derive the spectrum of the filtered output (4.155).