Microscope Image Processing

where u and n are spatial frequencies in the x and y directions, respectively.

The parameter f

c

, called the optical cutoff frequency, is given by

f

c

¼

1

r

o

¼

a

ld

i

(2:14)

2.5 Coherent Illumination

Some microscopy applications require the use of coherent light for illumination.

Lasers, for example, supply coherent illumination at high power. Coherent illu-

mination can be thought of as a distribution of point sources whose amplitudes

maintain fixed phase relationships among themselves. Diffraction works some-

what differently under coherent illumination, and the psf and OTF take

on different forms. Under coherent illumination, an optical system is linear in