Flexible geometrical calibration for fringe-reflection optical three-dimensional shape measurement

Accurate geometrical calibration is the basis of a fringe-reflection testing system, especially the calibration of reflection ray directions. However, such a calibration procedure is challenging because of two reasons: first of all, the common method of reflection ray directions calibration, which is based on the pinhole camera imaging model, fails in the presence of the pupil imaging aberration. What's more, although using a camera lens with an external stop in front can remove the pupil imaging aberration, it is difficult to achieve the exact geometrical measurement of the camera pinhole and the calibration of the reflection ray directions into the camera because of the low signal-to-noise ratio of images. In this paper, we introduce a new calibration method by finding the points on the liquid crystal display in front of the camera with different positions corresponding to the same camera pixels through correspondence matching. The calibration process and the results from the experiments on fringe-reflection testing demonstrate that the calibration method presented in this paper is simple, practical, and flexible. (C) 2015 Optical Society of America