film is also modeled in this simulation, both the pre-distortion and
film distortion must be included. To represent the overall effect,
the pre-distortion must be the same as the one to be used in the
production of the CGH. This pre-distortion model needs only to
provide the accuracy desired in the CGH. However, the model of the
film distortion must be as accurate as possible to provide an accurate
simulation of the overall transfer function. Thus, while a third or
fifth order fit may suffice for the pre-distortion, the model for the
film distortion may require a higher order or a spline fit.
The type of modulation utilized in the hologram is also modeled.
Recall that the pre-emphasis or phase-only filtering of the
information used to create the hologram is independent of the
modulation technique incorporated in the physical hologram. That is,
the hologram may be produced as an amplitude hologram with constant
phase but variable transmission, or produced as a phase hologram with
constant amplitude but variable phase. The proper choice of hologram
is modeled in the simulation by mapping the hologram pattern to
transmission or phase. This modified amplitude or phase pattern is
used as the reference and is multiplied by the Fourier transform of
the test image. The following steps of the correlation and analysis
are identical with the ideal correlation simulation with the exception
that the correlation peak is no longer centered on-axis.
Figure 7.8 shows the continuous-tone hologram of a square,
produced by the simulation. The carrier frequency was maximized in
this case as half the sampling frequency to produce the greatest
separation of the various output terms. The Fourier transform shown
in Figure 7.2, a since function, is spatially modulated by a sinusoidal