Digital Image Correlation-Assisted Phase Unwrapping for Temporal Phase Shifting Fringe Projection Profilometry
Objective The temporal phase shifting method is a widely used non-contact optical measurement method,with the advantages of full-field measurement,high speed,and high precision.Although the idea of phase unwrapping itself is simple,the irregular phase truncation contour caused by complex topography and various noises in the phase principal value image often inhibits the effect of the direct phase unwrapping method.In order to improve the measurement ability of complex topography and reduce the interference of noise,we propose a simple and effective phase unwrapping method for temporary phase shifting fringe projection profilometry by introducing the stereo digital image correlation(DIC)method.Methods First,four-step phase shifting fringe patterns are projected and collected,and an additional speckle pattern is projected onto the surface of the object to be measured,then the wrapped phase is calculated.Second,the Canny edge detection method is used to determine the position of the grayscale-jump contour line in the phase principal value image.Third,the depth of the pixels on contour line is calculated by DIC method.Fourth,the phase of the pixels on the contour line is estimated via the stereo DIC method.Fifth,the fringe order of the contour line is calculated based on the estimated phase.Sixth,the fringe order of the phase continuous region between the contour lines is calculated according to the fringe order on the contour lines.Lastly,the fringe order of the phase continuous region between the contour lines is combined with the fringe order on the contour lines to complete phase unwrapping.Results and Discussions The experiment shows that this method can achieve the measurement accuracy of the conventional multi-frequency heterodyne method,and it shows good adaptability to complex surface morphology and discontinuous phase distribution.It can automatically complete accurate phase unwrapping without human intervention.Conclusions The proposed method requires measuring only a small number of pixels using stereo DIC method.These pixels account for less than 10％of the total number of effective pixels.After the phase information of these pixels is obtained,a relatively simple and direct algorithm can be used to process pixels in other areas.Our method provides an effective means to handle complex surface phase measurement and offers a new idea for the situation requiring high measurement speed.
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