Displacement and strain calculations by the phase shift method.
The phase shift method, well known in holographic interferometry, is applied to the deformation of line gratings. The method uses the moire effect but it determines local displacement or strain from the grey values of three shifted images instead of the coordinates of the fringes. The basic equations are derived from the transmittance function. The theoretical error with respect to a given displacement field is calculated by simulation. Real errors are investigated by related plotter-generated line gratings. The phase shift method is especially suitable for automatic digital image processing.
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