Page 110 - Introduction to Information Optics

2.5. Image Processing with Optics 95

/Up)

-P -P 3
4
(a)

-.7T
- - fc -
•PA ~P3 -P2 'Pi ° PI P2 P3 PA P

Fig. 2.22. (a) Amplitude filter, (b) Phase filter.

in Fig. 2.23. We see that the degree of restoration increases rapidly as T m
decreases. However, as T m approaches zero, the transmittance of the inverse
filter also approaches zero, which leaves no transmittance of the inverse filter.
Thus, a perfect degree of restoration, even within the bandwidth, Ap, cannot
actually be obtained in practice. Aside from this consequence, the weak
diffracted light field from the inverse filter would also cause poor noise
performance. The effects on image restoration due to the amplitude, the phase,
and the combination of amplitude and phase filters are shown in Fig. 2.24. In
view of these results, we see that using the phase filter alone would give rise to
a reasonably good restoration result as compared with the complex filtering.
This is the consequence of the image formation (either in the spatial or in the