In this paper, the optical transfer function (OTF) of a digital imaging system is determined by different frequencies' sinusoidal gratings in two stages of before and after the Nyquist frequency. Before the Nyquist frequency, modulation transfer function (MTF) and visibility are equivalent, and the phase transfer function (PTF) does not change with phase variation of the initial object gratings. Sampling of the grating with frequency above the Nyquist frequency gives rise to sampling moire fringes. In this situation, the MTF is unusually bigger than 1 and is not equivalent to the visibility of the sampling moire, but the PTF shows two different behaviors before and after the Nyquist frequency. Before the Nyquist frequency, the PTF does not depend on the initial phase variation of the grating, but after the Nyquist frequency, the PTF depends on the initial phase variation. Therefore, the PTF of the sampling moire is proposed for phase variation detection. (C) 2017 Optical Society of America
展开▼
