correlation model, this model includes a step which creates the

computer-generated continuous-tone hologram.

 This hologram, when used as the reference filter, provides a

 correlation similar to an ideal correlation. However, the differences

 can be quite pronounced. For example, the output not only includes

 the correlation, but also the convolution and other terms. These

 terms may, in some cases, overlap and cause degradation of the signal-

 to-noise ratio. In all cases, light will be lost to the convolution

 term and the on-axis term with a resulting loss of total efficiency.

 Obviously, the hologram has a significant effect on the result of the

 optical correlator and must be adequately modeled to obtain reasonable

 predictions of correlator performance.

 The hologram produces not only the correlation plane but also

other terms. As was discussed in Chapter III, the space-bandwidth

requirement for the hologram is dependent on the spatial carrier

frequency and the number of points in the reference image. Thus,

based on these factors, the reference image must be padded in a field

of zeros of the appropriate space-bandwidth. This requires greater

padding than is needed in the ideal correlation and additional

computing power for analyzing the same images.

 In addition, there are modifications to the hologram which are

possible when produced via computer generation. These modifications,

discussed in the previous chapters, are modeled here to predict their

effect and usefulness. These hologram modifications include the use

of non-linear pre-distortion of the filter function to remove the

distorting film response. The pre-distortion of the filter function

would occur in the computer generation of the CGH. However, since the