A system for the automatic evaluation of interferograms

For the digitizing and processing of the interferograms from classical and holographic interferometers, a picture analysis system based upon a computer with a television digitizer was installed. Signal averaging, spatial smoothing, subtraction of the overlayed intensity function and the removal of distortion patterns using a spatial filtering technique in the frequency spectrum of the interferograms can be used. The extraction of fringe loci from the digitized interferograms is performed by a floating threshold method. The fringes are numbered using a special scheme after the removal of any fringe disconnections which appeared if there is not sufficient contrast in the holograms. The reconstruction of the object function from the fringe field is achieved by a local polynomial least squares approximation with spline fit. The averaging and subtraction of interferograms and the analysis of structures in the holographic interferograms of car tires as well as the evaluation of interferograms of transonic flows, are shown.