Half-Period Gray-Level Coding Strategy for Absolute Phase Retrieval

N-ary gray-level (nGL) coding strategy is an effective method for absolute phase retrieval in the fringe projection technique. However, conventional nGL contains many unwrapping errors at boundaries of codewords. In addition, number codewords limited only one pattern. Consequently, this paper proposes a new based on half-period coding, which can improve both these two deficiencies. Specifically, we embed every period with 2-bit codeword, instead 1-bit codeword. Then, special correction and decoding methods are proposed to correct calculate orders, respectively. The generate n2 n gray levels Moreover, insensitive moderate image blurring. Various experiments demonstrate robustness effectiveness strategy.