High-speed real-time 3-D coordinates measurement based on fringe projection profilometry considering

High-speed real-time 3-D coordinates measurement based on fringe projection profilometry considering camera lens distortion

Shijie Feng, Qian Chen, Chao Zuo, Jiasong Sun and Shi Ling Yu

Jiangsu Key Laboratory of Spectral Imaging & Intelligent Sense,

Nanjing University of Science and Technology, Nanjing, Jiangsu Province 210094, China

Abstract

Optical three-dimensional (3-D) profilometry is gaining increasing attention for its simplicity, flexibility, high accuracy, and non-contact nature. Recent advances in imaging sensors and digital projection technology further its progress in high-speed, real-time applications, enabling 3-D shapes reconstruction of moving objects and dynamic scenes. However, the camera lens is never perfect and the lens distortion does influence the accuracy of the measurement result, which is often overlooked in the existing real time 3-D shape measurement systems. To this end, here we present a novel high-speed real-time 3-D coordinates measuring technique based on fringe projection with the consideration of the camera lens distortion. A pixel mapping relation between a distorted image and a corrected one is pre-determined and stored in computer memory for real-time fringe correction. The out-of-plane height is obtained firstly and the acquisition for the two corresponding in-plane coordinates follows on the basis of the solved height. Besides, a method of lookup table (LUT) is introduced as well for fast data processing. Our experimental results reveal that the measurement error of the in-plane coordinates has been reduced by one order of magnitude and the accuracy of the out-plane coordinate been tripled after the distortions being eliminated. Moreover, owing to the generated LUTs, a 3-D reconstruction speed of 92.34 frames per second can be achieved.

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Citations

Feng, S., Chen, Q., Zuo, C., Sun, J., & Yu, S. L. (2014). High-speed real-time 3-D coordinates measurement based on fringe projection profilometry considering camera lens distortion. Optics Communications, 329, 44-56.

Results

Fig. 1. Measurement errors of the in-plane coordinates. (a) The measurement error in directions of X and Y when the lens distortion is not considered, (b) the measurement error in directions of X and Y when the presented method is used.

Fig. 2. Measurement errors of the out-of-plane coordinates. (a) The measured surface of gauge block with height of 50.48 mm when neglecting the lens distortion; (b) The measured surface of gauge block with height of 80.71 mm when neglecting the lens distortion; (c) The measured surface of gauge block with height of 50.48 mm when using the proposed method; (d) The measured surface of gauge block with height of 80.71 mm when using the proposed method.

Fig. 3. The real-time measurement result of multiple objects (Media).

Methods

Fig. 1. The linear camera model.

Fig. 2. Camera lens distortion.

Fig. 3. Calibration process for the unknown coefficients in governing equation.

Traditionally, to calibrate the measurement system accurately, gauge blocks of different sizes should be employed. However, the manufacturing of a mass of gauge blocks with high precision would be an extremely costly work. Therefore, to circumvent this issue, we develop an alternative approach without using multiple gauge blocks. Firstly we set a basic position for a calibration board as the reference plane and then make the board move along its normal direction which is shown in Fig. 3. Every time the calibration board forwards a fixed step and data points are selected on the surface of the calibration board at each position. The total number of the movements will largely rely on the height (depth) range of the measured object. Since the step size and the number of shifts can be set based on the actual requirement, this approach would be more flexible and practical than the strategy with use of gauge blocks.

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Contact

Shijie Feng

Ph.D. Candidate of NJUST

Email:geniusshijie@163.com ( or 311040574@njust.edu.cn)

Nanjing University of Science and Technology, Jiangsu Province (210094), P.R.China

Qian Chen

Dean of the school of Electronic and Optical Engineering

Email: chenqian@njust.edu.cn

Nanjing University of Science and Technology, Jiangsu Province (210094), P.R.China

Chao Zuo

Associate professor at the school of Electronic and Optical Engineering

Email: surpasszuo@163.com

Nanjing University of Science and Technology, Jiangsu Province (210094), P.R.China