Noise reduction is one of the most exciting problems in automatic fringe processing. We propose a two-dimensional (2-D) envelope transform for normalization of fringe patterns, coupled with spin filtering, to construct so-called noise-free normalized fringe patterns. The 2-D envelope transform uses correct fringe intensity envelopes for normalization of fringe patterns, i.e., for making the fringe background and amplitude constant over the whole field. Spin filtering is applied to fringe patterns for removal of random noise taking into account fringe flow. With spin filtering and the 2-D envelope transform, a noise-free normalized fringe pattern is constructed for postprocessing. Based on this improved fringe pattern, two local pixel transforms for strain extraction from a single moiré pattern are developed, in which the digital pure secondary moiré method is improved and the strain-field image method with division is developed.
© 1996 Optical Society of America
Original Manuscript: July 17, 1995
Revised Manuscript: January 16, 1996
Published: July 10, 1996
Qifeng Yu, Klaus Andresen, Wolfgang Osten, and Werner Jueptner, "Noise-free normalized fringe patterns and local pixel transforms for strain extraction," Appl. Opt. 35, 3783-3790 (1996)