  Wavefront sensing is a widely-used non-interferometric, single-shot, and
quantitative technique providing the spatial-phase of a beam. The phase is
obtained by integrating the measured wavefront gradient. Complex and random
wavefields intrinsically contain a high density of singular phase structures
(optical vortices) associated with non-conservative gradients making this
integration step especially delicate. Here, using a high-resolution wavefront
sensor, we demonstrate experimentally a systematic approach for achieving the
complete and quantitative reconstruction of complex wavefronts. Based on the
Stokes' theorem, we propose an image segmentation algorithm to provide an
accurate determination of the charge and location of optical vortices. This
technique is expected to benefit to several fields requiring complex media
characterization.
