Phase Unwrapping Method Based on Heterodyne Three Frequency Non-equal Step Phase Shift

This paper presents a phase unwrapping method of heterodyne three frequency non-equal step phase shift, to surmount disadvantages of needing dozens of images in 3-D measurement techniques of multi-frequency phase shift. The method selects three frequencies. Firstly, four-step phase-shifting algorithm is used to calculate wrapped phase and average intensity of the intermediate frequency. Then the wrapped phases of other frequencies are obtained utilizing two-step phase-shifting algorithm. Finally, the absolute phase is calculated using heterodyne method. In addition, the contour sine/cosine filter method is utilized to filter noise by the fringe orientation information. The 3-D points cloud of standard planar and calibration target are reconstructed experimentally. Then the planeness of standard planar is calculated. The centers of markers of calibration target are extracted to calculate distance between two adjacent circles. Experiments demonstrate that the proposed method reduces the number of fringe images, eliminates the effects of noise efficaciously.