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15 September 2008 Optical flow processing for sub-pixel registration of speckle image sequences
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In recent years digital image processing techniques have become a very popular way of determining strains and full-field displacements in the field of experimental mechanics due to advancements in image processing techniques and also because the actual process of measurement is simpler and not intrusive compared to traditional sensor based techniques. This paper presents a filtering technique which processes the polar components of the image displacement fields. First, pyramidal gradient-based optical flow is calculated between blocks of each two frames of a speckle image sequence while trying to compensate in the calculation small rotations and shears of the image blocks. The polar components of the resulting motion vectors - phase and amplitude - are then extracted. Each of the motion vector angle values is smoothed temporally using a Kalman filter that takes into account previously calculated angles located at the same spatial position in the motion fields. A subsequent adaptive spatial filter is used to process both the temporally smoothed angles and amplitudes of the motion field. Finally, test results of the proposed method being applied to a speckle image sequence that illustrates plastic materials being subjected to uniaxial stress and to artificial data sets are presented.
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Corneliu Cofaru, Wilfried Philips, and Wim Van Paepegem "Optical flow processing for sub-pixel registration of speckle image sequences", Proc. SPIE 7073, Applications of Digital Image Processing XXXI, 70731A (15 September 2008);

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