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Open AccessArticle

Recognition and Matching of Clustered Mature Litchi Fruits Using Binocular Charge-Coupled Device (CCD) Color Cameras

1
Key Laboratory of Key Technology on Agricultural Machine and Equipment, Ministry of Education, South China Agricultural University, Guangzhou 510642, China
2
School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, China
3
School of Mechanical and Electrical Engineering, Foshan University, Foshan 528000, China
*
Authors to whom correspondence should be addressed.
Sensors 2017, 17(11), 2564; https://doi.org/10.3390/s17112564
Received: 21 September 2017 / Revised: 1 November 2017 / Accepted: 4 November 2017 / Published: 7 November 2017
(This article belongs to the Special Issue Charge-Coupled Device (CCD) Sensors)
Recognition and matching of litchi fruits are critical steps for litchi harvesting robots to successfully grasp litchi. However, due to the randomness of litchi growth, such as clustered growth with uncertain number of fruits and random occlusion by leaves, branches and other fruits, the recognition and matching of the fruit become a challenge. Therefore, this study firstly defined mature litchi fruit as three clustered categories. Then an approach for recognition and matching of clustered mature litchi fruit was developed based on litchi color images acquired by binocular charge-coupled device (CCD) color cameras. The approach mainly included three steps: (1) calibration of binocular color cameras and litchi image acquisition; (2) segmentation of litchi fruits using four kinds of supervised classifiers, and recognition of the pre-defined categories of clustered litchi fruit using a pixel threshold method; and (3) matching the recognized clustered fruit using a geometric center-based matching method. The experimental results showed that the proposed recognition method could be robust against the influences of varying illumination and occlusion conditions, and precisely recognize clustered litchi fruit. In the tested 432 clustered litchi fruits, the highest and lowest average recognition rates were 94.17% and 92.00% under sunny back-lighting and partial occlusion, and sunny front-lighting and non-occlusion conditions, respectively. From 50 pairs of tested images, the highest and lowest matching success rates were 97.37% and 91.96% under sunny back-lighting and non-occlusion, and sunny front-lighting and partial occlusion conditions, respectively. View Full-Text
Keywords: litchi recognition; harvesting robot; binocular vision; stereo matching litchi recognition; harvesting robot; binocular vision; stereo matching
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Wang, C.; Tang, Y.; Zou, X.; Luo, L.; Chen, X. Recognition and Matching of Clustered Mature Litchi Fruits Using Binocular Charge-Coupled Device (CCD) Color Cameras. Sensors 2017, 17, 2564.

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