An imaging system (200) including a phase-modulating element (202) configured and arranged with optics (100) in an imaging path (300) of the imaging system, to modulate light emitted from an object (150), while the object is in motion with respect to the imaging system, to create a modified point-spread function (PSF); and a processor (700) configured and arranged to generate, on an image plane (500) of the imaging system, a three-dimensional image from the modulated light to provide depth-based characteristics of the object. Other applications are also described.