incident on the filter plane. The filter is placed precisely to
the position where it is recorded. The amplitude component of
interest transmitted by the filter is the term-by-term product
of: Bg.(14) and (159)
N
F. 541. 2. R/ Aj FC - n5. Nn). exp{- j2xt X¢ } (16)
After the Fourier transform produced by L2, a filtered image
appears in the (xi,yı) coordinates system. The amplitude in the
image plane becomes
N
f" (x.yi =r 3 fG.yi)ei?*nPoXi (17)
n-—N
where all constant are collected in the complex amplitude r,.
The deblurred image carries a grating structure, which can be
removed by the band-pass filtering process.
Finally, linearity of the deblurring process with respect
to irradiance is achieved by photographing the output with
y=-%, with this value of vy, the irradiance transmittance of the
film is proportional: to f(xv.¥: )=
IV. Feature Analysis of the New System
The multi-channel inverse filtering system has many advan-
tages.
1°. The large dynamic range
The dynamic range (DR) of a hologram is defined as the
largest range in which the amplitude transmittance is propor-
tional to the exposure. The larger the dynamic range is, the
higher the deblurring ratio of the inverse filtering system is.
The. deblurring ratio is the compression ratio of the blur
width.For the absorptive filter,its dynamic range is restrained
by straight part of the H-D curve.Because holographic filter is
attenuating Jdight by diffraction, its; dynamic range: ds res-
trained. in the. straight part of the t-E curve (the curve;: of
transmittance vs exposure).
It is well-known that the holographic plate has a big
Gamma. Therefore, its dynamic range is small. We find a special
photographic processing technique which can make the quasi-
linear recording range to be 500:1, so the mask |H'"|^' does not
affect the dynamic range of the inverse filter.
The small DR isa problem which has not been solved pro-
perly, because the capacity of the film is far from enough for
the realization of linear holographic recording. So the effects
of special photographic processing techniques are limited. The
method reported here is to compress the exposure range with the
aid of the attenuating mask, so the exposure that the film sub-
jected is allmost equal everywhere. It does not require the
film to have a large linear region, therefore the filter ge-
nerated by this system has a large dynamic range than that made
by other methods.
2°. The high efficiency
If the hologram is used as a inverse filter, the intensity
of reference beam must be very small in comparision with that
of the object beam. The weaker the reference is, the higher the
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