Main content area

Identifying immature and mature pomelo fruits in trees by elliptical model fitting in the Cr–Cb color space

Liu, Tian-Hu, Ehsani, Reza, Toudeshki, Arash, Zou, Xiang-Jun, Wang, Hong-Jun
Precision agriculture 2019 v.20 no.1 pp. 138-156
algorithms, color, computer vision, fruits, harvesting, least squares, lighting, models, precision agriculture, pummelos, trees
In precision agriculture, identification of fruit in trees is important. Furthermore, it is also essential for estimating the yield, targeting the exact location for a harvesting robot and selectively harvesting the fruit. An elliptical boundary model-based machine vision algorithm was developed to identify immature and mature pomelo fruit in trees. In the proposed solution, the images were converted from RGB space to Y′CbCr space. Then, ordinary least-squares (OLS) was introduced in fitting implicit second order polynomials of elliptical boundary models in the Cr–Cb color space for segmenting immature green fruits, mature green, green partial white, green partial yellow and green partial red fruits. Those elliptical boundary models along with area opening mathematical morphology and diameter thresholding were applied in the identification procedure. The algorithm was tested on a set of 200 validation images acquired under natural illumination conditions. The results of the validation test showed that the total correct identification rate was 93.5%. The total false positive, missed rate, repeated rate and merged rate were equal to 8.2, 6.5, 10.2 and 10.6%, respectively. The proposed method performed better in detecting mature fruit, the color of which is different from green, than in detecting immature green fruit. On average, the segmenting time for 640 × 480 and 1280 × 960 images were 0.134 and 0.200 s, respectively and the total identification time for 640 × 480 and 1280 × 960 images were 0.240 and 0.362 s, respectively.