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A. Vander Lugt, Opt. Acta 15, 1 (1968).
A. Vander Lugt, IEEE trans. Inform. Theory IT-10, 139 (1964).
Optical spatial filters were made to identify the letters “B”, “E”, and “F”. The response of these three filters to an input “B” is shown in (a). Linear combinations of those filters were chosen to set the cross-correlation terms to zero. Thus testing the input “B” for its identifty to “E” or “F” yields a null response as shown in “b” where, of course, the test for “B” yields unit response. A rotated input “B” gave the responses shown in (c) to the original filters and the responses shown in (d) for the linear combinations of filters. For ease of comparison, the responses in each case (a, b, c, and d) were divided by the appropriate constant to set the “B–B” responses equal to one. Clearly discrimination among characters has been enhanced by the linear combination technique.
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