Phase measuring deflectometry (PMD) has been widely studied to obtain three-dimensional (3D) shape of specular surfaces. Due to the procedure of slope integration, complicated specular components having discontinuous surfaces cannot be measured by the existing PMD methods. This paper presents a novel Direct PMD (DPMD) method to solve this problem of measuring discontinuous specular objects. A mathematical model is established to directly relate the absolute phase and depth data. Then a hardware measuring system has been set up. The system parameters are calibrated by using a plane mirror and a translating stage. 3D shape of an artificial specular step, a monolithic multi-mirror array having multiple specular surfaces and a reflected diamond distribution surface has been measured. The experimental results verified that the proposed method based on DPMD successfully measured full-field 3D shape of specular objects having discontinuous surfaces accurately and effectively.
Lateral chromatic aberration (CA) of color cameras has great effects on the imaging quality. This paper presents a novel method to full-field calibrate lateral CA between color channels by using unwrapped phase data. Closed circle sinusoidal fringe patterns having the optimum three-fringe numbers are generated and displayed on a liquid crystal screen consecutively through red, green and blue channels. These closed fringe patterns are captured by a color camera. The wrapped phase and unwrapped phase of each pixel can be calculated by using four-step phase shifting algorithm and optimum three-fringe number method, respectively. The pixel deviations produced by lateral CA are computed by comparing the obtained absolute phase data between red, blue, and green channels in polar coordinate system and calibration is accomplished in Cartesian coordinate system. Lateral CA between color channels of the color camera can be compensated by using the calibrated data. Simulated and experimental results show the validity of the proposed calibration and compensation method.