Abstract: 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 "I.sub.1 " of a pixel in a first of such shadow moire fringe patterns is approximated by I.sub.0 +Acos.o slashed., the light intensity "I.sub.2 " of the pixel in a second of such shadow moire fringe patterns is approximated by I.sub.0 +Acos[.o slashed.+(.pi./2)], the light intensity "I.sub.3 " of the pixel in a third of such shadow moire fringe patterns is approximated by I.sub.0 +Acos[.o slashed.+.pi.], and the light intensity "I.sub.4 " of the pixel in a fourth of such shadow moire fringe patterns is approximated by Acos[.o slashed.+(3.pi.)/2)]. The phase values ".o slashed." are equal to arctan((I.sub.2 -I.sub.4)/(I.sub.1 -I.sub.3), and a first two-dimensional array of phase values are calculated.

Abstract: A system for measuring surface characteristics of an electronic interconnection component, such as a printed circuit board, by analyzing shadow moire patterns. Printed circuit boards are carried on a continuous conveyor under a grating. For each printed circuit board, a shadow moire fringe pattern is created in response to a determination that the printed circuit board is properly located under a grating and within the field of view of a camera. Fringes of the shadow moire fringe pattern are quantified over one or a multiple of analysis paths to determining if the printed circuit board is unacceptably warped, in which case a signal is generated. For each printed circuit board, multiple images can be captured and mathematically combined, by image subtraction, to produce an enhanced shadow moire fringe pattern that is analyzed for warpage.