Effect of different weight initialization strategies on transfer learning for plant disease detection

The weight initialization technique for transfer learning refers to the practice of using pretrained models that can be modified to solve new problems, instead of starting the training process from scratch. In this study, six different transfer learning weight initialization strategies were proposed for plant disease detection: scratch (i.e., random initialization), pretrained model on cross-domain (ImageNet), model trained on related domain (ISIC 2019), model trained on related domain (ISIC 2019) with cross-domain (ImageNet) weights, model trained on same domain (PlantVillage), and model trained on same domain (PlantVillage) with cross-domain weights (ImageNet). Weights from each strategy were transferred to a target dataset (Plant Pathology 2021). These strategies were implemented using eight deep learning architectures. It was observed that transferring from any strategy led to an average acceleration of convergence ranging from 33.88% to 73.16% in mean loss and an improvement of 8.72%-42.12% in mean F1-score compared to the scratch strategy. Moreover, although smaller and less comprehensive than ImageNet, transferring information from the same domain or related domain proved to be competitive compared to transferring from ImageNet. This indicates that ImageNet, which is widely favoured in the literature, may not necessarily represent the most optimal transfer source for the given context. In addition, to identify which strategies have significant differences, a post hoc analysis using Tukey's HSD test was conducted. Finally, the classifications made by the proposed models were visualized using Grad-CAM to provide a qualitative understanding of how different weight initialization strategies affect the focus areas of the models. Six transfer learning weight initialization strategies for plant disease detection were proposed, showing a 33.88%-73.16% faster convergence and an 8.72%-42.12% improvement in F1-score over random initialization.image