A layered modulation method for pixel matching in online phase measuring profilometry

• The captured fringe patterns are enhanced by Retinex theory for better modulation distribution.
• The object modulation is divided into multiple layers based on iterative Otsu method.
• The high, medium and low modulation reflect more comprehensive information of object contour.
• The frame displacement is calculated based on centroid concept with selected modulation layers.
• Numerical simulations are detailed and experimental results verify the validity and feasibility of the proposed approach.

An online phase measuring profilometry with new layered modulation method for pixel matching is presented. In this method and in contrast with previous modulation matching methods, the captured images are enhanced by Retinex theory for better modulation distribution, and all different layer modulation masks are fully used to determine the displacement of a rectilinear moving object. High, medium and low modulation masks are obtained by performing binary segmentation with iterative Otsu method. The final shifting pixels are calculated based on centroid concept, and after that the aligned fringe patterns can be extracted from each frame. After performing Stoilov algorithm and a series of subsequent operations, the object profile on a translation stage is reconstructed. All procedures are carried out automatically, without setting specific parameters in advance. Numerical simulations are detailed and experimental results verify the validity and feasibility of the proposed approach.