1 January 1991 Three-dimensional surface inspection using interferometric grating and 2-D FFT-based technique
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A new method, based on a combination of interferometric grating projection and 2D digital FFT-based phase measurement, is presented for 3D shape measurement and surface inspection. This technique can generate a grating pattern focusing everywhere in its illumination space; thus, it has infinity focus depth. This capability makes it possible to improve measurement sensitivity by increasing the projection angle without losing the grating focus, making it more suitable for surface inspection of a large object. The sinusoidal intensity distribution of the grating, the monotonic phase nature of the fringe pattern coded on the object surface, and the phase information spectra clustered in the frequency domain make data deduction by this technique not only possible, but more accurate.
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Y.Y. Hung, Y.Y. Hung, Shouhong Tang, Shouhong Tang, Quiming Zhu, Quiming Zhu, } "Three-dimensional surface inspection using interferometric grating and 2-D FFT-based technique", Proc. SPIE 1332, Optical Testing and Metrology III: Recent Advances in Industrial Optical Inspection, (1 January 1991); doi: 10.1117/12.51120; https://doi.org/10.1117/12.51120

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