  In this article, we report an imaging method, termed Fourier ptychographic
microscopy (FPM), which iteratively stitches together a number of variably
illuminated, low-resolution intensity images in Fourier space to produce a
wide-field, high-resolution complex sample image. By adopting a wavefront
correction strategy, the FPM method can also correct for aberrations and
digitally extend a microscope's depth-of-focus beyond the physical limitations
of its optics. As a demonstration, we built a microscope prototype with a
resolution of 0.78 um, a field-of-view of ~120 mm2, and a resolution-invariant
depth-of-focus of 0.3 mm (characterized at 632 nm). Gigapixel colour images of
histology slides verify FPM's successful operation. The reported imaging
procedure transforms the general challenge of high-throughput, high-resolution
microscopy from one that is coupled to the physical limitations of the system's
optics to one that is solvable through computation.
