New calibration approach for 3D measurement system based on the light-source-stepping method

摘要

In the 3D measurement system based on light-source-stepping method, phase shift changes with the depth of the objectchanges. The phase distribution recovered by N-step phase shifting method is distorted and then the recovered 3D shapeis distorted. Fujigaki proposed the whole-space tabulation method to obtain 3D shape without distortion. The movingstage is used to calibrate the system and then the whole-space look-up tables are constructed. It is inconvenient tocalibrate the measurement system. We proposed a new method to calibrate the system without moving stage. Firstly, thecamera is calibrated by Zhang’s method. Secondly, a reference plane with sparse marks is placed at different depth ofmeasurement volume. The fringes are projected on the plane and the images are captured at the same time. Thirdly, thephase of different depth is worked out by improved Fourier transform profilometry method. The phase of marker isestimated by local curve fitting. The image coordinates of markers are detected. The projection matrix from referenceplane to image plane is worked out from the image coordinates and world coordinates of markers and the innerparameters of camera. The 3D coordinates of every pixel of reference plane are worked out from their image coordinatesand the projection matrix. Fourthly, a whole-space look-up table is constructed. This method does not need precisemoving stage to calibrate the relationship between phase and 3D coordinates. The hardware requirement for systemcalibration is simplified. Experiments are carried out to verify the proposed method.