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Fringe Analysis In Chapters 3 and 6–9 we have given a description of classical interferometry, holographic interferometry, moir´ , speckle and photoelasticity. The outcome of all these techniques is e a set of fringes called interferograms. For many years, the analysis of these interferograms has been a matter of manually locating the positions and numbering of the fringes. With the development and decreasing cost of digital image processing equipment, a lot of effort has been made into what is termed digital fringe pattern measurement techniques | Optical Metrology. Kjell J. Gasvik Copyright 2002 John Wiley Sons Ltd. ISBN 0-470-84300-4 11 Fringe Analysis INTRODUCTION In Chapters 3 and 6-9 we have given a description of classical interferometry holographic interferometry moire speckle and photoelasticity. The outcome of all these techniques is a set of fringes called interferograms. For many years the analysis of these interferograms has been a matter of manually locating the positions and numbering of the fringes. With the development and decreasing cost of digital image processing equipment a lot of effort has been made into what is termed digital fringe pattern measurement techniques. It is three main reasons for this effort 1 to obtain better accuracy 2 to increase the speed 3 to automate the process. In this chapter some of the basic principles of digital fringe pattern analysis will be described. In Section we describe techniques which intend to be a direct replacement of the human brain - eye combination by detecting the positions of the fringes. In Sections and techniques for continuous determination of the phase of the fringe function are described. For more detailed discussions of digital fringe pattern measurement techniques the book edited by Robinson and Reid 1993 is recommended. A comparison of the different techniques is performed by Kujawinska 1993b and Perry and McKelvie 1993 . INTENSITY-BASED ANALYSIS METHODS Introduction Before the development of the phase-measurement techniques described in Sections and intensity-based techniques were the only image-processing tools available for the automatic analysis of interferograms. They still are important methods in fringe analysis and are sometimes the only viable technique for interferograms which have been retrieved from photographic records or which have been obtained from interferometers in which it is impossible or impractical to introduce phase-measuring techniques. They may also be appropriate .

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