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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