The gamma nonlinearity of the digital projector leads to obvious phase errors in the phase measuring profilometry. Based on the Fourier spectrum analysis of the captured pattern, a robust gamma correction method is proposed in this paper. An orthogonal sinusoidal grating precoded with two different known gamma values is used to evaluate the gamma value of the pattern. The evaluated gamma value is then encoded into the computer-generated phase-shifting fringe patterns before the fringe patterns are sent to the digital projector, which makes the captured fringe patterns well-sinusoidal and alleviates the phase errors caused by the gamma nonlinearity. Compared with other gamma correction methods, only one captured pattern is needed to evaluate the gamma value without loss of the accuracy. With the proposed method, a fast and accurate three-dimensional shape measurement can be achieved using the conventional three-step phase-shifting algorithm. Experiments have verified its feasibility and validity.
The deficiency of CCD's sampling time resulted from slow shooting frequency and breaking surface of measured
object bring some difficulties to the three-dimensinal surface restoration of dynamic process. A novel method of
three-dimensinal restoration with marked fringes tracking for high movement process is proposed in this paper, and the
problems caused by deficiency of sampling and breaking fringes are solved, the proper three-dimensinal shape of
measured object is obtained. Computer simulation and experiment have proved the feasibility of this method.