Although hologram interferometry has had numerous and widespread applications, it has faced two persistent impediments that derive from the photographic nature of holography itself. Traditionally holograms have been recorded in photographic materials which require chemical or thermoelectric processing before they can be used to generate an image. This constitutes the first impediment: a significant time delay between the deformation of an object and the observation of that deformation as fringes in a holographic interferogram. The second impediment has been the pictorial nature of the fringes themselves. Converting fringe data to numerical data is a difficult process that is time consuming and subject to considerable error. Of the considerable work that has been done to remove these impediments, the two developments that stand out most are the real-time fringe display systems such as Electronic Speckle Pattern Interferometry (ESPI) and its relatives, and phase-step interferometers.