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From Harvest to Market: Non-Destructive Bruise Detection in Kiwifruit Using Convolutional Neural Networks and Hyperspectral Imaging
oleh: Sajad Ebrahimi, Razieh Pourdarbani, Sajad Sabzi, Mohammad H. Rohban, Juan I. Arribas
Format: | Article |
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Diterbitkan: | MDPI AG 2023-08-01 |
Deskripsi
Fruit is often bruised during picking, transportation, and packaging, which is an important post-harvest issue especially when dealing with fresh fruit. This paper is aimed at the early, automatic, and non-destructive ternary (three-class) detection and classification of bruises in kiwifruit based on local spatio-spectral near-infrared (NIR) hyperspectral (HSI) imaging. For this purpose, kiwifruit samples were hand-picked under two ripening stages, either one week (7 days) before optimal ripening (<i>unripe</i>) or at the optimal ripening time instant (<i>ripe</i>). A total of 408 kiwi fruit, i.e., 204 kiwifruits for the ripe stage and 204 kiwifruit for the unripe stage, were harvested. For each stage, three classes were considered (68 samples per class). First, 136 HSI images of all undamaged (healthy) fruit samples, under the two different ripening categories (either <i>unripe</i> or <i>ripe</i>) were acquired. Next, bruising was artificially induced on the 272 fruits under the impact of a metal ball to generate the corresponding bruised fruit HSI image samples. Then, the HSI images of all bruised fruit samples were captured either 8 (<i>Bruised-1</i>) or 16 h (<i>Bruised-2</i>) after the damage was produced, generating a grand total of 408 HSI kiwifruit imaging samples. Automatic 3D-convolutional neural network (3D-CNN) and 2D-CNN classifiers based on PreActResNet and GoogLeNet models were used to analyze the HSI input data. The results showed that the detection of bruising conditions in the case of <i>the unripe</i> fruit is a bit easier than that for its <i>ripe</i> counterpart. The correct classification rate (CCR) of 3D-CNN-PreActResNet and 3D-CNN-GoogLeNet for <i>unripe</i> fruit was 98% and 96%, respectively, over the test set. At the same time, the CCRs of 3D-CNN-PreActResNet and 3D-CNN-GoogLeNet for <i>ripe</i> fruit were both 86%, computed over the test set. On the other hand, the CCRs of 2D-CNN-PreActResNet and 2D-CNN-GoogLeNet for <i>unripe</i> fruit were 96 and 95%, while for <i>ripe</i> fruit, the CCRs were 91% and 98%, respectively, computed over the test set, implying that early detection of the bruising area on HSI imaging was consistently more accurate in the <i>unripe</i> fruit case as compared to its <i>ripe</i> counterpart, with an exception made for the 2D-CNN GoogLeNet classifier which showed opposite behavior.