Development of multiple regression model to estimate the apple’s bruise depth using thermal maps

• We used thermography for non-destructive bruise detection/depth prediction.
• We predicted bruise depths at upper, middle and lower regions of the apple surface.
• We used image registration for generating thermal maps of the affected regions.
• Thermal contrast between region of interest and the background was not required.

Thermography is a useful technology for non-contact two-dimensional temperature measurement of the material’s surface that requires nondestructive evaluation. It is also considered as a non-destructive method to determine quality attributes of agricultural products. In this study, the surface temperature of bruised apples was determined using thermal maps and the bruise depth during a set of factorial experiments in the form of a completely randomized design with two factors, namely impact location (bottom, middle, top) and impact energy at three levels (200, 700, 1200 mJ). Then, the relationship between bruise depth and surface temperature was investigated using multiple regression analysis. The results of analysis of variance showed that impact energy and the interaction of impact energy and location of impact region had a significant effect on temperature. The results of the multiple regression model showed that the surface temperature measured from a region can be used to predict the bruise depth in that region. The residual analysis confirmed the prediction adequacy of the proposed model.