Wave-front coding is a system level design method which can be used to extend the depth of field of an incoherent
optical system. By attaching a phase mask to the aperture, the optical transfer function can not only be made insensitive
to misfocus, but also can avoid the isolated zeros caused by defocus. With this modified optical transfer function, a
purposely blurred image can be obtained and its corresponding clear one with large depth of focus can be generated
through digital processing techniques, such as direct inverse filtering, wiener filtering and maximum entropy restoration
and so on. This is why the wave-front coded imaging system is called optical/digital hybrid imaging system as well.
The most important part of the system design lies in the design of phase masks. So far, many kinds of phase masks have
been suggested; among all those types, two are classical: cubic-phase-mask and logarithmic-phase-mask. However,
whether an optimum phase mask exists or not is still a question that is not answered yet. This paper focuses on this
question and tries to find one answer. In this paper, considering several critical factors and with the help of a simulation
program developed by ourselves, we make a comparison among the performance of different phase masks and finally
propose a prototype phase mask whose performance is acceptable in several aspects.