A sequence of image processing algorithms for the analysis of interference patterns generated by a phaseshifting speckle interferometer is discussed. The goal is the accurate determination of displacement and strain components at the surface of an object. The phase change related to the displacement is accurately calculated from eight digitized interference patterns using a phase-shifting algorithm. Digital image processing algorithms have been developed for phase unwrapping, phase restoration, and phase fitting. During the processing steps a binary mask is used to solve the problem of invalid areas. Experimental results for the strain components at the surface of a simple object demonstrate a repeatability of 0.3-microstrain rms.

A sequence of algorithms for processing interference patterns generated by a phase -shifting speckle interferometer is discussed. The processing yields the computation of in -plane displacement and strain components on the surface of an object, using a phase-shifting algorithm to compute the phase. Accurate phase measurement on a 512 *512 grid is achieved by pixel -synchronous digitizing of four interference patterns and subsequent calculation of the phase modulo 2n radians, using a two -dimensional look -up table. A pipeline of Datacube image processing modules is configurated to perform this measurement. Digital image processing algorithms have been developed for phase unwrapping, phase restoration and smoothing. During these processing steps, invalid pixels due to low modulation or saturation are neglected. For phase unwrapping an algorithm has been developed that, starting at a chosen start pixel, propagates a "wavefront" of unwrapped phase data through the data set and that takes a set of neighbouring pixels into account to detect 2Et steps. Subsequently, phase restoration is done by averaging valid neighbouring pixels. Basic binary image processing techniques are used to solve the problem of irregularly shaped objects due to holes and shadows. The measured phase change is used to compute the inplane displacement and strain components of the deformed object. Results of a measurement of in -plane displacement and strain components on the surface of a simple aluminium object are shown.

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A digital phase shifting speckle interferometric technique for measuring the 3D displacement vector field and the in -plane strain components of a deformed object is presented. The displacement components at each point on the surface of the object are calculated by subtracting the measured phases before and after deformation. Accurate phase measurement in each detector point is achieved by using reference beam phase shifting, fast digitizing of the interference patterns and image processing techniques. The 3D displacement vector can be calculated from measurements of the displacement components along four sensitivity vectors. Application of a special gradient filter enables the determination of the in -plane strain components. Special purpose hardware allows a complete measurement of the phase change modulo 2rc on a 512 *512 grid every 240 ms. The measuring system and its performance will be discussed and results of measurements of the in -plane strain components in a simple experimental aluminium object are shown. For small loads the estimated inaccuracy amounts to 0.3 µstrain r.m.s..

To determine the in-plane strain components from the 3D displacement vector data of a loaded object, its shape has to be known. The phase shifting speckle interferometric system, &scried in this paper, has been used for both the displement vector measurements and for the acquisition of the essential shape information. The numerical shape data resulting from the application of a phase shifting technique allows further calculations, e.g. the determination of the object surface nonnal vector. The shape measurement method (a modified two-illumination-source technique) is discussed and the experimental system is described. An overview of the basic image processing algorithms, involved in the evaluation of the speckle interference patterns, is given. Improved algorithms concerning phase unwrapping and intensity averaging in the case of low light levels are presented more extensively. Results of shape measurements on a metal cube and a glass bottle are shown. The shape measurement error is estimated at 0.1 mm r.m.s.