Stable and Flexible Calibration Method for Telecentric Microvision System

In fringe projection profilometry (FPP), telecentric lens is usually used to narrow the measurement field of view (FOV) when measuring small objects. The imaging process of the telecentric system differs from the classical pinhole imaging principle, necessitating a new calibration method. Presently, calibration techniques used for telecentric systems persist in following the conventional practice of separating intrinsic and extrinsic parameters, leading to imprecise system parameters. To tackle this issue, we present a novel joint calibration approach founded on the homography matrix. Our approach concurrently optimizes both the intrinsic and extrinsic parameters, effectively mitigating issues associated with invalid extrinsic parameters and fluctuating intrinsic parameters observed in existing methods. In addition, the sign ambiguity concerning extrinsic parameters is successfully resolved, even in the absence of a precise positioning stage. This approach necessitates only a single adjustment in the pose of the planar calibration target, without any additional equipment requirements. Consequently, it can be flexibly applied across various domains where precise data acquisition of small objects is essential. This proposed method is evaluated in terms of calibration and reconstruction through contrast experiments, which demonstrate its feasibility and accuracy.