Preshift Phase Coding for 3-D Sensing That Avoids Fringe Order Errors With Extended Number of Codewords

Phase-shifting profilometry (PSP) based on phase coding has been a prevalent technique in 3-D sensing for its high-speed and high-efficiency advantages. However, the measurement accuracy is seriously affected by the fringe order errors caused by encoding phase instability and the mismatch problem between the wrapped phase and the corresponding fringe order. In this article, a novel preshift phase-coding (PSPC) method for 3-D sensing is proposed to ensure both the accuracy and robustness of the measurement. The preshift strategy is reflected in two directions. One is to preshift the position of all traditional phase-coding (TPC) fringes by half a period to make the fringe order completely misaligned with the wrapped phase. Another is to preshift the codeword value by half an order to avoid the occurrence of error-prone regions. Utilizing the preshift method can suppress most of the phase jump errors. In addition, combining the frequency-increased PSPC fringes with the introduced reference absolute phase enables the doubling of the measurement frequency while maintaining the number of codewords, thereby extending the measurement range. The simulation and experimental results demonstrate that the proposed method effectively avoids fringe order errors and improves the robustness and accuracy of the measurement.