The state-of-art camera calibration method requires the user to provide accurate pixel coordinates of calibration plate feature points. For some cameras with special sensing range, general calibration objects' (such as calibration plates with a centimeter-long dimension) using range is outside their clear sensing range. Using these cameras to take a picture for general calibration objects, you can only get out-of-focused blurred images that can not accurately extract feature points' pixel coordinates. This paper analyzes the influence on the phase of the structured light based on sine grating (abbreviated as sinusoidal structured light) when optical system is in defocus state. Based on the fact that the state of focus is independent of the phase of sinusoidal structured light, a method of phase-shifted sinusoidal structured light encoding by phase shift is proposed to encode the feature points on the calibration object and this method realizes the calibration of the camera under out-of-focus condition. The experimental results show that the maximal deviation of focal length from the real value is 0.47% and the maximal pixel reprojection error is 0.17 pixels. This paper provides a solution to camera calibration with a special sensing range.
Camera calibration method based on phase encoding for out-of-focus condition
First published at:Jul 01, 2018
1 Salvi J, Armangué X, Batlle J. A comparative review of camera calibrating methods with accuracy evaluation[J]. Pattern recognition, 2002, 35(7): 1617–1635. DOI:10.1016/S0031-3203(01)00126-1
2 Qiu M L, Ma S D, Li Y. Overview of camera calibration for computer vision[J]. Acta Automatica Sinica, 2000, 26(1): 43–55.
3 Abdel-Aziz Y I, Karara H M, Hauck M. Direct linear transformation from comparator coordinates into object space coordinates in close-range photogrammetry[J]. Photogrammetric Engineering & Remote Sensing, 2015, 81(2):103–107.
4 Faig W. Calibration of close-range photogrammetry systems: Mathematical formulation[J]. Photogrammetric Engineering and Remote Sensing, 1975, 41(12): 1479–1486.
5 Tsai R. A versatile camera calibration technique for high-accuracy 3D machine vision metrology using off-the-shelf TV cameras and lenses[J]. IEEE Journal on Robotics and Automation, 1987, 3(4): 323–344. DOI:10.1109/JRA.1987.1087109
6 Zhang Z. A flexible new technique for camera calibration[J]. IEEE Transactions on Pattern Analysis and Machine Intelligence, 2000, 22(11): 1330–1334. DOI:10.1109/34.888718
7 Guo T, Da F P, Fang X. Camera calibration under small field of view[J]. Chinese Journal of Lasers, 2012, 39(8): 164–168
8 Wang Y W, Chen X C, Tao J Y, et al. Accurate feature detection for out-of-focus camera calibration[J]. Applied Optics, 2016, 55(28): 7964–7971. DOI:10.1364/AO.55.007964
9 Szeliski R. Computer vision: algorithms and applications[M]. New York: Springer, 2010: 45–51.
10 Shi A J, Bai R L, Tian Q H. 3D measurement based on structured light using a combination of Gray code and line-shift patterns[J]. Opto-Electronic Engineering, 2016, 43(11): 26–32. DOI:10.3969/j.issn.1003-501X.2016.11.005
石爱军, 白瑞林, 田青华. Gray码结合线移的结构光三维测量[J].光电工程, 2016, 43(11): 26–32. DOI:10.3969/j.issn.1003-501X.2016.11.005
11 Lin J Y, Huang J Q, Jiang K Y. Subregional Gamma pre-coding correction for phase error compensation[J]. Opto-Electronic Engineering, 2016, 43(9): 32–38.
12 Zhang W Z. Structured-light three dimensional measurement method based on digital projector[D]. Hangzhou: Zhejiang University, 2015.
13 Li B W, Karpinsky N, Zhang S. Novel calibration method for structured-light system with an out-of-focus projector[J]. Applied Optics, 2014, 53(16): 3415–3426. DOI:10.1364/AO.53.003415
Supported by Jiangsu Science and Technology Project (Industry Support) (BE2014082), Kunshan Robotics and Intelligent Equipment Technology Project (KSJ1517), and Zhejiang Research on Application of Commonweal Technology(2017C31080)
Get Citation: Yang Hao, Cai Ning, Lin Bin, et al. Camera calibration method based on phase encoding for out-of-focus condition[J]. Opto-Electronic Engineering, 2018, 45(7): 180100.