MEASURING SURFACE FLATNESS USING SHADOW MOIRE TECHNOLOGY AND PHASE-STEPPING IMAGE PROCESSING

摘要

A two- dimensional array of phase values is calculated from digitized phase- shifted shadow moire fringe patterns that are indicative of the flatness of the surface of an object. The light intensity "I1" of a pixel in a first of such shadow moire fringe patterns is approximated by I0+AcosØ the light intensity "I2" of the pixel in a second of such shadow moire fringe patterns is approximated by I0+Acos[Ø+(pi/2)], the light intensity "I3" of the pixel in a third of such shadow moire fringe patterns is approximated by I0+ Acos[Ø+pi], and the light intensity "I4" of the pixel in a fourth of such shadow moire fringe patterns is approximated by Acos[Ø+(3pi)/2]. The phase values "Ø" are equal to arctan (I2-I4) /(I1-I3), and a first two-dimensional array of phase values are calculated. A plurality of two-dimensional arrays of image values are calculated from a first two-dimensional array of phase values, and the two-dimensional arrays of image values are filtered. A second two- dimensional array of phase values is calculated from the filtered two- dimensional arrays of image values. Discontinuities between adjacent phase values in the second two-dimensional array of phase values are identified by searching along a plurality of one-dimensional arrays of the two- dimensional array of phase values, and those discontinuities are adjusted. After the first row and, thereafter, the first column is searched, the other rows are sequentially searched, and thereafter the other columns may be sequentially searched.