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