Anisotropic spiral phase filtering for image enhancement in edge detection and microscopy

摘要

The spiral phase plate (SPP) with an azimuthal structure ψ(ρ,Φ) = exp[iΦ] (0 < Φ < 2π) has been used as a filter in a 4f system to achieve edge enhancement. Generally such edge-enhanced effect is isotropic, i.e., each edge of the input pattern is enhanced to the same degree regardless of its orientation. In this report we show that one can achieve anisotropic edge enhancement by breaking down the symmetry of the filtering process. This can be done in two ways: First, by use of a fractional spiral phase filter with a fractional topological charge and a controllable orientation of the edge dislocation, and second, by using an off-axis SPP. In the first method, the degree and orientation of enhancement are controlled by the value of the topological charge and the starting angle of the SPP. While in the second method, the two parameters are determined by the position of the singularity. In this report we apply both these techniques in edge detection and microscopy.