Computer image processing techniques for the measurement of vibration amplitude are presented, which utilize phase-shifted time-average holographic interferograms. The calculation of the square root and division with phase-shifted interferograms gives a high contrast fringe pattern which contours the vibration amplitude. The arctangent calculation with phase-shifted fringe patterns also gives the phase distribution proportional to the optical path difference of the measured object before and after vibration. The detection of the phase discontinuity of ±π in the phase image gives exactly the center line of the dark fringe. The distribution of the vibration amplitude can be obtained by the fringe-order determination and its interpolation. The bias deformation of the vibration is obtained by the correction of phase discontinuities of ±2π and ±π in the phase images before and after vibration.
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