Flexible 3-d shape measurement using projector defocusing

Abstract

We present a 3-D shape-measurement technique using a defocused projector. The ideal sinusoidal fringe patterns are generated by defocusing binary structured patterns, and the phase shift is realized by shifting the binary patterns spatially. Because this technique does not require calibration of the gamma of the projector, it is easy to implement and thus is promising for developing flexible 3-D shape measurement systems using digital video projectors. Optical Society of America OCIS codes: 120.0120, 120.2650 3-D shape measurement is very important to numerous disciplines; over the years, a number of techniques have been developed, including some with real-time capability To perform high-quality 3-D shape measurement using a digital fringe projection and phase-shifting method, projector gamma calibration is usually mandatory. This is because the commercial video projector is usually a nonlinear device that is purposely designed to compensate for human vision. A variety of techniques have been studied, including the methods to actively change the fringe to be projected This Letter will present a flexible 3-D shape measurement technique without requiring gamma calibration. The idea came from our two observations: (1) seemingly sinusoidal fringe patterns often appear on the ground when the light shines through open window blinds and (2) the sharp features of an object are blended together in a blurring image that is captured by an out-of-focus camera. The former gives the insight that an ideal sinusoidal fringe image could be produced from a binary structured pattern, and the latter provides the hint that if the projector is defocused, the binary structured pattern might become ideal sinusoidal. Because only binary patterns are needed, the nonlinear response of the projector would not be a problem, because only 0 and 255 intensity values are used. Moreover, phase shifting can be introduced by spatially moving the binary structured patterns. Therefore, if this hypothesis is true, a flexible 3-D shape measurement system based on a digital fringe-projection technique can be developed without nonlinear gamma calibration. Experiments will be presented to verify the performance of the proposed technique. Sinusoidal phase-shifting methods are widely used in optical metrology because of their measurement accuracy Solving these three equations, this phase can be obtained: ͑x,y͒ = tan This equation provides the wrapped phase with 2 discontinuities. A spatial phase-unwrapping algorithm can be applied to obtain continuous phas