Ptychography is a scanning variation of the coherent diffractive imaging method for providing high-resolution
quantitative images from specimen with extended dimensions. Its capability of achieving diffraction-limited spatial
resolution can be compromised by the sample thickness,
which is generally required to be thinner than the depth
of field of the imaging system. In this Letter, we present
a method to extend the depth of field for ptychography
by numerically generating the focus stack from reconstructions with propagated illumination wavefronts and combining the in-focus features to a single sharp image using an
algorithm based on the complex-valued discrete wavelet
transform. This approach does not require repeated measurements by translating the sample along the optical axis
as in the conventional focus stacking method, and offers a
computation-efficient alternative to obtain high-resolution
images with extended depth of fields, complementary to the
multi-slice ptychography