3D profile measurement of complex metal workpieces based on adaptive polarization projection

Adaptive fringe projection technology is widely used in three-dimensional (3D) contour measurement of high dynamic range objects, due to its ability to accurately locate highlight areas in images, transforming rough global highlight elimination into fine local highlight elimination. However, this grayscale-based method is often affected by the surface structure of the object and ambient light, requiring multiple levels of exposure intensity, resulting in reduced stability and measurement efficiency. To solve this problem, an adaptive polarization projection method(APPM) is innovatively proposed in this paper, replacing the traditional grayscale mode with a polarization mode. By thoroughly analyzing the polarization characteristics and depolarization mechanisms of metal surface highlights, a polarization depolarization model for the tested object's surface was established, based on its image saturation response. The complex metal workpiece surface is thereby segmented into a polarization reflection dominant region and a diffuse scattering depolarization region. This achieves accurate identification and quantification of polarization characteristics within highlight regions from a single exposure intensity. Simultaneously, polarization information was organically integrated with a high-density fringe encoding scheme to construct an adaptive polarization encoding strategy. This strategy enables localized, highly stable, efficient, and high-precision highlight elimination. Experimental results demonstrate that, when compared with conventional fringe projection contour measurement methods and existing highlight removal techniques, this method simultaneously enhances both the efficiency and accuracy of measuring complex metal workpieces, all while maintaining robust stability.