Phase Measurement Deflectometry With Concave Mirror-Assisted Clear Imaging

Phase measuring deflectometry (PMD) is usually used to measure the specular surface accurately. However, due to the limited depth of field (DOF) of the camera lens, the traditional PMD cannot image the specular surface under test (SUT) and the display clearly together. As a result, the pixel position extraction and linear tracking of the display during the system calibration process and the process of the gradient solution are fuzzy and the measurement stability is reduced. According to the principle of concave mirror paraxial reflection imaging, this article introduces a concave mirror into the PMD and proposes a new PMD based on concave mirror (CM-PMD)-assisted imaging. The system model, calibration, and reconstruction methods are studied. The accuracy and reliability of the proposed CM-PMD method are verified by quantitative comparison experiments with the traditional PMD method. The experimental results demonstrate that the proposed CM-PMD method can effectively reduce the image blur caused by the inherent DOF of the camera and improve the precision and depth range of specular measurement.