New Optical Distortion Measuring Method Using Digital Image Analysis of Projection-Moire Patterns

Optical distortion of images observed through windshields is due to the geometry to a small degree, but to a larger extent, due to effects occurring in production. The detection of manufacturing defects is of primary concern for on-line and off-line inspection procedures. Zebra patterns commonly used to detect serious windshield defects only yield qualitative and highly subjective results. This new method uses fine Moiré screens projected through the inspected windshield on a master grating, directly yielding a full-field fringe pattern directly revealing the line-of-sight deviation. PC-based Digital Image Analysis of the Moiré Fringes permits nearly instantaneous quantitative evaluation yielding a two-dimensional map of distortion levels and deviations. Complete derivation of Fringe-order relations to the measured distortion parameters is included in this paper, as well as a description of the software used in Digital Image Analysis.