Edge Detection Features to Evaluate Hardness of Dates Using Monochrome Images

Date is an important fruit in the regular diets of many peoples in the Arab countries and several other parts of the world. Hardness is one of the important attributes in determining the quality of dates. Hard dates are tough, difficult to chew, unsuitable for several product preparation and ultimately fetching low market price. In general, hard dates have strong curvy and zigzag textured skin. In this study, the efficiency of edge detection features in classifying dates based on hardness using monochrome images was determined. Date samples (Fard variety) were obtained from three major dates growing regions in Oman, and classified into three grades (soft, semi-hard and hard) by a group of trained graders followed with a confirmation by an experienced grader in a commercial dates company. Individual dates were imaged using a monochrome camera (600 dates per grade; total = 1,800 images). A total of 36 features were extracted (28 in spatial domain and 8 in frequency domain) using edge detection methods. An artificial neural network (ANN) was used to classify the dates based on hardness. The overall classification accuracies were 75 % and 87 % while using single ANN (irrespective of regions) for three-class (soft, semi-hard and hard) and two-class (soft and hard (semi-hard and hard together)) models, respectively. While using separate ANN for each region in the three-class model, the mean classification accuracies were 94 %, 59 % and 84 % for soft, semi-hard and hard dates, respectively. Similarly, for the two-class ANN model for each region, the accuracies were 95 % and 77 % for soft and hard dates, respectively. Edge detection features have a great potential in determining several surface qualities of food and agricultural products, where similar gray or color values but varying texture are found.