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Sensors 2017, 17(10), 2361; https://doi.org/10.3390/s17102361

Camera Calibration Robust to Defocus Using Phase-Shifting Patterns

1
Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei 230026, China
2
Department of Instrument Science and Opto-Electronics Engineering, Hefei University of Technology, Hefei 230088, China
3
School of Automation, Wuhan University of Technology, Wuhan 430070, China
*
Authors to whom correspondence should be addressed.
Received: 16 August 2017 / Revised: 10 October 2017 / Accepted: 12 October 2017 / Published: 16 October 2017
(This article belongs to the Section Physical Sensors)
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Abstract

Camera parameters can’t be estimated accurately using traditional calibration methods if the camera is substantially defocused. To tackle this problem, an improved approach based on three phase-shifting circular grating (PCG) arrays is proposed in this paper. Rather than encoding the feature points into the intensity, the proposed method encodes the feature points into the phase distribution, which can be recovered precisely using phase-shifting methods. The PCG centers are extracted as feature points, which can be located accurately even if the images are severely blurred. Unlike the previous method which just uses a single circle, the proposed method uses a concentric circle to estimate the PCG center, such that the center can be located precisely. This paper also presents a sorting algorithm for the detected feature points automatically. Experiments with both synthetic and real images were carried out to validate the performance of the method. And the results show that the superiority of PCG arrays compared with the concentric circle array even under severe defocus. View Full-Text
Keywords: defocus; camera calibration; phase-shifting; feature points; concentric circle defocus; camera calibration; phase-shifting; feature points; concentric circle
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Cai, B.; Wang, Y.; Wang, K.; Ma, M.; Chen, X. Camera Calibration Robust to Defocus Using Phase-Shifting Patterns. Sensors 2017, 17, 2361.

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