Camera calibration using a 2D planar board is widely applied because of the flexibility and simplicity of this method. However, this technique fails to yield reliable and accurate calibration results when an imperfect planar target is used. The accuracy of the image and world coordinates for the extracted corners, which are prerequisites for deriving precise camera parameters, are affected by the lens distortion and the non-planarity of the calibration target. In this paper, the accuracy of the obtained image coordinates is improved by combining a Hilbert transform with a traditional calibration method. In addition, the geometry of the calibration target is fully considered so as to acquire precise world coordinates using an overall nonlinear parameter optimization algorithm. The reprojection error of the proposed method is reduced by 80% compared with the traditional method for a significantly deformed planar target, which demonstrates the superiority of the proposed camera-calibration technique.
Fringe projection three-dimensional measurement is widely applied in a wide range of industrial application. The traditional fringe projection system has the disadvantages of high expense, big size, and complicated calibration requirements. In this paper we introduce a low-cost and portable realization on three-dimensional measurement with Pico projector. It has the advantages of low cost, compact physical size, and flexible configuration. For the proposed fringe projection system, there is no restriction to camera and projector’s relative alignment on parallelism and perpendicularity for installation. Moreover, plane-based calibration method is adopted in this paper that avoids critical requirements on calibration system such as additional gauge block or precise linear z stage. What is more, error sources existing in the proposed system are introduced in this paper. The experimental results demonstrate the feasibility of the proposed low cost and portable fringe projection system.
A new geometrical model and mathematical method for three-dimensional surface reconstruction with phase- shifting structured light technique is proposed. First, with the proposed method, there will be no restriction to camera and projector's relative alignment on parallelism and perpendicularity. Furthermore, the depth map can be directly derived from the phase map by a simple function. The x and y coordinates are inferred from the depth z coordinate. Second, no special calibration hardware is needed; a simple two-step plane-based calibration procedure is adopted to acquire the system intrinsic and extrinsic parameters. Third, a look-up-table compensation method is presented to avoid the accumulation of errors introduced in the structured light system. The experimental results demonstrate the e®ectiveness and accuracy of the proposed methods.