Hyperspectral imaging-based early damage degree representation of apple: a method of correlation coefficient

Early damage detection of fruit is a challenge in the postharvest treatment of agricultural products, especially the lack of early damage degree representation. In this study, the damage distribution of apples was experimentally investigated through impact tests based on hyperspectral imaging technology. A parameter–correlation coefficient Cfg is proposed to characterize the damage distribution of fruit. The damage index DIx is further defined to measure the damage degree. This method uses the distribution of the correlation coefficient field to evaluate the damage and determines the relationship between the reflectance and the drop height. The index gradually increases with the rise in drop height. The damage index DI0.6 was 0.2106, 0.2925, and 0.3585 at the drop heights of 0.3 m, 0.6 m, and 0.9 m, respectively. The results of the damage distribution were also interpreted using the finite element method. This non-destructive method can be used to reflect the damage distribution of apples under impact accurately, which provides a solid basis for assessing early damage in postharvest fruit.