Abstract
Due to the change of illumination environment and overlapping conditions caused by the neighboring fruits and other background objects, the simple application of the traditional machine vision method limits the detection accuracy of lychee fruits in natural orchard environments. Therefore, this research presented a detection method based on monocular machine vision to detect lychee fruits growing in overlapped conditions. Specifically, a combination of contrast limited adaptive histogram equalization (CLAHE), red/blue chromatic mapping, Otsu thresholding and morphology operations were adopted to segment the foreground regions of the lychees. A stepwise method was proposed for extracting individual lychee fruit from the lychee foreground region. The first step in this process was based on the relative position relation of the Hough circle and an equivalent area circle (equal to the area of the potential lychee foreground region) and was designed to distinguish lychee fruits growing in isolated or overlapped states. Then, a process based on the three-point definite circle theorem was performed to extract individual lychee fruits from the foreground regions of overlapped lychee fruit clusters. Finally, to enhance the robustness of the detection method, a local binary pattern support vector machine (LBP-SVM) was adopted to filter out the false positive detections generated by background chaff interferences. The performance of the presented method was evaluated using 485 images captured in a natural lychee orchard in Conghua (Area), Guangzhou. The detection results showed that the recall rate was 86.66%, the precision rate was greater than 87% and the F1-score was 87.07%.
Highlights
Lychees are one of the most popular fruits and are widely cultivated in the hilly regions of southernChina [1,2]
He et al proposed a method of green lychee recognition that used an improved linear discriminant analysis (LDA) classifier for classifying pixels and Hough transform circle detection to locate the fruit of lychee by the spherical shape features; this method provides a 76.4% recognition accuracy of clustered lychee fruits
Lychee fruit detection in an orchard environment using theand classifier. target samples were extracted from the training images to train the support vector machine (SVM) classifiers using histogram intersection kernel (HIK), linear and
Summary
Lychees are one of the most popular fruits and are widely cultivated in the hilly regions of southernChina [1,2]. Zhuang et al proposed a detection method using the combination of marker-controlled watershed transform (MCWT) and convex hull operation to locate citrus fruits in overlapped and occluded conditions Their algorithm performs an average in detecting lychee clusters; the watershed transform algorithm is sensitive to complex texture disturbances on lychee fruit surfaces [18]. He et al proposed a method of green lychee recognition that used an improved linear discriminant analysis (LDA) classifier for classifying pixels and Hough transform circle detection to locate the fruit of lychee by the spherical shape features; this method provides a 76.4% recognition accuracy of clustered lychee fruits.
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