Fourier transform method for automatic processing of moiré deflectograms

Abstract

In this work, a Fourier transform technique for automatic analysis of moire deflectograms is presented. A squared grating is used to multiplex the information of the deflection in two orthogonal directions in one image. This procedure avoids the necessity of rotating the gratings to obtain the complete deflection information. With this method only two fringe patterns. reference and distorted, are needed to determine the complete deflection information. To deal with irregularly shaped processing areas, a Gerchberg extrapolation method is used. The automatic determination of the carrier as well as the size and position of the reconstruction windows permit the complete and automatic measurement of the deflection produced by an ophthalmic lens in two orthogonal directions. Afterwards, the refractive power maps can be obtained, Experimental results obtained with a progressive addition lens are presented and comparison with measurements obtained with a commercial focimeter are shown showing a good agreement.