Phase error analysis and reduction in phase measuring deflectometry

In phase measuring deflectometry (PMD), the inspection accuracy of the defects and height of the specular surface are related to the level of phase errors. The usage of numeric integration in reconstructing the shape and the defocusing capture of the fringe pattern, which will amplify the phase errors, make error discussion more significant in PMD than other shape measurement techniques. Phase error analysis and reduction in PMD are presented. The random noises, nonlinear response function, the nontelecentric imaging of the charge-coupled device camera, and the nonlinear response function of the liquid crystal display screen are the main phase error sources in PMD. The analytical relation between the random phase error and its influence factors in PMD is deduced. From the relation formulation, the influence factors of random phase error are analyzed, and the results are proven by the simulation and experiment. A possible phase error-reduction method, which integrates several methods for congeneric errors in fringe projection profilometry, is investigated to reduce phase errors in PMD. This composite method is proven to have a good performance by a plane mirror experiment.