Gamma correction for three-dimensional object measurement by phase measuring profilometry

For structured light technique using commercial digital projector, gamma distortion is an inevitable factor affects the accuracy and resolution of the final measurement result seriously. This paper presents a gamma correction method based on the response function of the whole system, which is calculated from the input and output grayscale, and then the actual projected fringe patterns could be got. Through projecting these corrected fringes, the measurement error induced by gamma distortion would be reduced. At the same time, a low-pass filter has been designed to eliminate the residual high order harmonics in the deformed fringe patterns captured by a camera, in the basis of a mathematical model of the high order harmonics which are caused by gamma nonlinearity. Both computer simulation and experiment have been conducted to demonstrate the validity of this method.