Finally, a few comments about the restoration filter in (135) are in order.
Even though the restoration filter in (135) looks somewhat similar to the
Wiener filter in (41b) (which can also be implemented in the discrete case
by taking a sufficiently large number of samples in the wi;-plane), there are
important differences between the two. While the Wiener filter gives the best
restoration in an average sense for a family of pictures, the formula here
gives an optimum restoration for the one degraded picture that is to be
restored. Also, the derivation of the Wiener filter required the basic assump-
tion that the
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