Addressing Class Imbalance in Image-Based Plant Disease Detection: Deep Generative vs. Sampling-Based Approaches

Abstract

Deep learning-based classifiers for object recognition and classification have been used in the domain of plant disease detection, particularly lesions from leaf images. In such domains, as expected, deep neural networks perform better using balanced data sets than imbalanced ones, as they exhibit some inductive bias favoring balanced data from each class. However, data sets for plant disease detection are often imbalanced due to the rarity of disease lesions in real-world settings. While deep generative approaches such as generative adversarial networks (GANs) have been established as an effective means of augmenting high-dimensional image data, the literature lacks a detailed study of the effectiveness of GAN-based models on a plant disease detection task, compared to sampling-based approaches traditionally used to reduce the skewness of the data. In this paper, we comparatively evaluate an image classifier based on a dense convolutional neural network (CNN), trained using a GAN, versus the same CNN model used in tandem with undersampling, oversampling, and an adaptation of the Synthetic Minority Over-sampling Technique (SMOTE). The GAN-based approach is shown to attain significantly higher recall and hence F-measure and ROC AUC against each of these.