Page 111 - Introduction to Information Optics

96 2. Signal Processing with Optics

L.
amplitude transmittance L m

Fig. 2.23. Degree of restoration as a function of T m

Fourier domain); the phase distribution turns out to be a major quantity in
the effect of image processing as compared with the effect due to amplitude
filtering alone. In other words, in image processing, is as well as image
formation, the amplitude variation, in some cases, can actually be ignored. A
couple of such examples are optimum linearization in holography and phase-
preserving matched filters.
Let us now provide an image restoration result we obtained from such an
inverse filter, shown in Fig. 2.25, in which we see that a linear blurred image
can indeed be restored. In addition, we have also seen that the restored image
is embraced with speckle noise, also known as coherent noise. This is one of the
major concerns of using coherent light for processing. Nevertheless, coherent
noise can be actually suppressed by using an incoherent light source, as will be
discussed in Sec. 2.8.