Cover story: Wang S Y, Liu Y K, Yu X. A scanning micro phase measuring profilometry based on optical flow pixel matching[J]. Opto-Electron Eng, 2024, 51(11): 240194

In scanning PMP, it is essential to first match different positions of the object to the same point, and then extract phase information using phase-shifting algorithms. Both pixel-matching accuracy and phase-shifting algorithms influence measurement precision. To address this, a microscopic system is employed, leveraging its telecentric optical path characteristics to achieve equal conversion between object displacement and pixel displacement. By alternately capturing white-field and fringe images, precise pixel matching is realized through optical flow in the white-field images, followed by accurate pixel matching of the fringe images based on the object's uniform motion. A set of N fringe images, closely matching a full cycle based on the initial fringe period, is selected to compute the truncated phase distribution using an arbitrary step phase-shifting method. The optimal fringe period is then identified through a probability density function, leading to the accurate extraction of phase information and the completion of the object morphology measurement. Experimental results demonstrate that the proposed method significantly enhances measurement accuracy, with the phase-shifting algorithm applying to any N≥3 images, making it particularly suitable for 3D measurements of objects in industrial production lines, achieving an RMSE measurement accuracy of about 0.008 mm.