Improved phase-coding methods with fewer patterns for 3D shape measurement

Absolute phase information is required when multiple separated objects are being measured. The recent proposed phase-coding method can effectively achieve absolute phase retrieval by embedding the fringe order information in phase domain. However, it suffers from the limitation of codewords and the requirement of more coding patterns. To overcome these problems, this paper proposed several improved phase-coding methods to solve the absolute phase with fewer patterns. The four-frame and five-frame method are suitable when the fringes are sparse, since they can respectively encode N/2 and N fringe periods(generally N <= 16). If really dense fringe patterns with more than N periods are required, the improved two-step phase-coding algorithm can be adopted since it can encode about N-2/2 fringe periods. Experiments were conducted and the results verify the success of the proposed methods. (C) 2017 Elsevier B.V. All rights reserved.