The effect of the quantization of the fringe intensity on the phase error in phase shifting measurement is formulated. An expression of the statistical relationship between the measured phase error and the fringe intensity error is presented. The expansion of the intensity error in Fourier series allows to obtain an analytic expression for the variance of the phase given by a standard N sample algorithm. A numerical simulation is performed, and its result is in good agreement with the analytic one. Several factors influencing the quantization effects are discussed.