Intrinsic parameter-free calibration of FPP using a ray phase mapping model

Flexible and accurate system calibration method in microscopic fringe projection profilometry

The three-dimensional (3D) measurement task of complex microstructures holds paramount significance in the domains of precision manufacturing and inspection. The calibration of the 3D system heavily determines the final reconstruction accuracy. The widely adopted system calibration method is phase-height mapping (PHM) and stereo vision (SV) based. The former can be applied directly to the calculation without considering the imaging model of the system, but it relies on highly precise and expensive translation stages or standard blocks. The latter's accuracy cannot be guaranteed because it is difficult to accurately calibrate the projector. In this paper, we establish an optically coupled microscopic fringe projection profilometry system that consists of a Scheimpflug pinhole projector and a super-low distortion bi-telecentric camera. We introduce a simplified 3D system calibration approach that combines phase modulation transfer and ray propagation. Our method enables the simultaneous calibration of the system, including the calibration of the projector, camera, and the phase to a 3D coordinates relationship, using only a 2D target. The calibrated projector's external parameters are used to obtain the target's complete poses, and then the direct mapping coefficients of the phase to the 3D coordinates can be obtained through the optical geometry structure and phase labels. Comparable experiments verify the feasibility of the proposed method.

Pixel-wise rational model for a structured light system

This Letter presents a novel structured light system model that effectively considers local lens distortion by pixel-wise rational functions. We leverage the stereo method for initial calibration and then estimate the rational model for each pixel. Our proposed model can achieve high measurement accuracy within and outside the calibration volume, demonstrating its robustness and accuracy.

Rapid and flexible calibration of DFPP using a dual-sight fusion target

The parameter calibration of a digital fringe projection profilometry (DFPP) system is a fundamental step and directly related to 3D measurement accuracy. However, existing solutions based on geometric calibration (GC) suffer from the weakness of limited operability and practicality. In this Letter, a novel, to the best of our knowledge, dual-sight fusion target is designed for flexible calibration. The novelty of this target is the ability to directly characterize control rays for ideal pixels of the projector, and to transform the rays into the camera coordinate system, which replaces the traditional phase-shifting algorithm and avoids the error from the nonlinear response of the system. Attributed to the excellent position resolution of a position-sensitive detector within the target, the geometric relationship between the projector and camera can be easily established by projecting only one diamond pattern. Experimental results demonstrated that the proposed method using only 20 captured images is capable of achieving comparable calibration accuracy to the traditional GC method (20 images versus 1080 images, 0.052 pixels versus 0.047 pixels), which is suitable for rapidly and accurately calibrating the DFPP system in the 3D shape measurement field.