Determination and applications of contoured windows for ESPI fringe pattern processing

摘要

Speckle fringe patterns of ESPI are full of high-spatial-frequency and high contrast speckle noise which defies normal process methods. Filtering with contoured windows has been proven to be an efficient approach to filter off the speckle noise while reserving the fringe patterns obtained by subtraction of two original speckle patterns. Furthermore, with contoured windows, the contoured correlation fringe pattern (CCFP) method proposed by the authors can derive high-quality fringe patterns of ESPI with speckle-free, smooth, normalized and consistent fringes from two original speckle patterns. CCFP method can also extract the phase field with a single-step phase-shifting. Determination of contoured windows is a key step in CCFP method. The contoured windows used to be determined by fringe orientations only and this process would generate accumulated errors. In this paper, two new algorithms to determine the contoured windows according to the fringe intensity slope and the distance ratio to neighboring skeletons with the help of the local fringe direction are proposed. These new techniques can determine contoured windows more precisely and more robustly with no accumulated errors. Some applications of our new contoured windows are also presented.