# Microscopic 3D measurement of shiny surfaces based on a multi-frequency phase-shifting scheme

## TL;DR

This paper introduces a multi-frequency phase-shifting scheme for microscopic 3D measurement of shiny surfaces, overcoming issues of fringe saturation and defocus to achieve high-accuracy surface reconstruction.

## Contribution

It proposes a novel multi-frequency phase-shifting method that extracts phases from unsaturated fringe regions, improving 3D reconstruction of shiny surfaces.

## Key findings

- Successfully reconstructs complete shiny surface morphologies.
- Achieves high measurement accuracy better than one micron.
- Demonstrates effectiveness on various metal surfaces.

## Abstract

Microscopic fringe projection profilometry is a powerful 3D measurement technique with a theoretical measurement accuracy better than one micron provided that the measured targets can be imaged with good fringe visibility. However, practically, the 3D shape of the measured surface can hardly be fully reconstructed due to the defocus of the dense fringes and complex surface reflexivity characteristics, which lead to low fringe quality and intensity saturation. To address this problem, we propose to calculate phases of these highlighted areas from a subset of the fringe sequence which is not subjected to the intensity saturation. By using the proposed multi-frequency phase-shifting scheme, the integrity of the 3D surface reconstruction can be significantly improved. The ultimate phase maps obtained from unsaturated intensities are used to achieve high-accuracy 3D recovering of shiny surfaces based on a phase stereo matching method. Experimental results on different metal surfaces show that our approach is able to retrieve the complete morphology of shiny surfaces with high accuracy and fidelity.