An absolute phase technique for 3D profile measurement using four-step structured light pattern

The aim of this paper is to develop a four-step pattern encoding strategy through the combination of a triangle waveform, a step waveform, and two square waveforms. The proposed pattern encoding strategy makes the range of unique phase distribution up to 10π, which is 5 times as large as 2π of conventional four-step phase shifting encoding approach. Therefore, the proposed encoding strategy enables the structured light-based measurement system to measure complicated objects without ambiguity, which is the common limitation of the phase shifting algorithms. Furthermore, the proposed strategy is a pixel-level method, leading to a high-density 3D reconstruction. The decoding approach is a pixel independent computation, which can eliminate the error propagation and enhance the reliability. The phase errors between the phase shifting and the proposed encoding strategy are compared by the numerical simulation and they are very close. Experiments with different objects are carried out to validate the robustness and accuracy for the proposed encoding strategy. The results show that it is efficient for the 3D reconstruction of complicated objects.