low frequencies are used, considerable rotation can occur with little

effect on correlation. If high frequencies are used, the cross-

correlation drops quickly with rotation. Thus, a matched filter

created from a high-pass image to discriminate against out-of-class

targets will not correlate well on in-class targets with small

changes. That is, as more high frequency emphasis is applied to the

matched filter, the discrimination sensitivity is increased. The

probability of false alarm is increased, but the probability of

detection drops. The high frequency emphasis is then tied to the Pd

and Pfa which must be specified for a particular application.

 There is another advantage to the frequency emphasis of matched

filters. As seen in equation 2.35, the transmission of the hologram

at each point depends on the magnitude of the reference image Fourier

transform. Yet the hologram transmission cannot be greater than 1.

Depending on the dynamic range of the film, the transmission out at

the edge of the hologram corresponding to the high frequencies is very

low or zero. As the magnitude drops off for high frequencies, so does

the transmission of light through the holographic filter, and hence,

filter efficiency is low. However, if the high frequencies are

emphasized (boosted), the transmission at those points in a positive

hologram is likewise emphasized. This creates an overall increase in

the hologram transmission. In an absorption hologram, the light which

is not transmitted is absorbed and lost to the system. The throughput

or efficiency is highly dependent on the total transmission of the

hologram. Thus, by emphasizing the high frequencies, the efficiency

of the Vander Lugt filter is increased. Because the maximum

transmission is limited to 1 and the dynamic range is limited on the