  Edge-enhanced microscopes with q-plate have been attracted more attention to
enhance the edges of phase-amplitude objects in biological sample due to their
capability for all-directional edge enhancement, while differential
interference-contrast microscopy enhances edges in only one-direction. However,
the edge-enhanced microscopes cannot distinguish the edges of phase and
amplitude objects, as both edges are equally enhanced. This study introduces a
novel method for isolating the edge of a phase object from an amplitude object
using an off-axis q-plate filter in a 4f system. Herein, we combined off-axis
q-plates with four different displacements to isolate the phase object edge
from the amplitude object. To demonstrate the proposed method, we conducted
experiments using two distinct samples. The first sample comprised a phase test
target surrounded by an aperture, and the second sample involved an overlap
between the phase test target and a white hair with non-zero transmittance. In
the samples, the isolated phase object edge is in good agreement with the
theoretical expectations, and the amplitude object edge was reduced by
approximately 93%. The proposed method is a novel and effective approach for
isolating the edge of a phase object from an amplitude object and can be useful
in various biological imaging applications.
