Fig. 1. Process of three-frequency heterodyne phase unwrapping method

Fig. 2. Analysis of phase-jump errors. (a) Phase error in the first process; (b) phase error in the second process; (c) phase error in the third process; (d) phase error of ?₁

Fig. 3. Initial fringe orders correction method based on periodic identification

Fig. 4. Phase-jump error by flooring. (a) Result of N₁ obtained by flooring function; (b) result of N₁ obtained by rounding function

Fig. 5. Diagram of phase error of N₁

Fig. 6. N₁ before and after correction

Fig. 7. Flowchart of the reverse correction method of N_i

Fig. 8. Images on flat board. (a) Physical image; (b) grating image captured by camera

Fig. 9. Comparative analysis of the results of flat experiment. (a) 3D diagram of absolute phase before correction by this method; (b) 3D diagram of absolute phase after correction by this method; (c) graph is plotted by randomly selecting the 100th row of data from Fig. 9(a) and Fig. 9(b)

Fig. 10. Comparative analysis of the results of circuit board experiment. (a) Physical image of circuit board; (b) grating modulation image of circuit board; (c) top view of reconstruction model before correction; (d) top view of reconstruction model after correction;(e) side view of reconstruction model before correction; (f) side view of reconstruction model after correction