A three-dimensional measurement system calibration method based on red/blue orthogonal fringe projection

Abstract

Structured light measurement system that consists of a camera and a projector has been widely used in three-dimensional (3-D) shape measurement. The premise of measurement is to calibrate the structured light system, and the calibration accuracy directly affects the accuracy of 3-D measurement system. The traditional calibration board-based methods suffer from either complex operations or uncompetitive accuracy. To overcome these limitations, this paper proposes a novel calibration method by introducing a liquid crystal display (LCD) with holographic projection film as a phase target to simplify the operations and improve the speed and accuracy of system calibration. The proposed calibration procedures are given as follows: Firstly, the LCD is turned on and kept still to display the red/blue orthogonal fringe pattern, and it is then turned off to reflect the projected fringe pattern with the holographic projection film, the brightness and frequency of the two patterns are adjusted and captured; Secondly, the accurate absolute phase maps are obtained using optimized phase calculation and overall error compensation method; Finally, the above two steps are repeated at several different positions and orientations in the measured field of view. The one-to-one correspondence between the camera and the projector pixel coordinate system and the phase target world coordinate system is established by using the phase equality, and the intrinsic and extrinsic parameters of the system are obtained to reconstruct 3-D shape of the objects. The experiment results demonstrate that the proposed method is feasible and the equipment is simple, which can effectively reduce the overall error, ensure the synchronous calibration of the camera and the projector, avoid the problem of time-consuming, and eventually improve the accuracy of the system calibration.