Computational grayscale dithering phase measuring deflectomerty for accurate specular surface inspection

•Present a complementary software solution for expanding measurement field.•Develop a surface adaptative fringe pattern to eliminate the defocused effect.•Factorizes the phase-height optimization with the estimated defocused level.•Accuracy and reliability are verified by quantitative comparison experiments. Specular surface can be precisely measured by phase measuring deflectometry, but the precision is affected by the enlarged virtual image depth range along the specimen. This paper develops a surface adaptative fringe pattern generation method to eliminate the out-of-focus effect, which dithers the fringe pattern, compensates the defocused effect and factorizes the phase-height optimization with the estimated equivalent defocused level segmentally. The accuracy and reliability are verified by quantitative comparison experiments of specular steps and the deformed screen topography reconstruction. The experimental results demonstrate that the proposed method flexibly reduces the image blurring and the phase-map error caused by the reflected light varies along the surface and the restriction of the camera's field of view.