Self-supervised visual representation learning on food images

Food image classification is the groundwork for image-based dietary assessment, which is the process of monitoring what kinds of food and how much energy is consumed using captured food or eating scene images. Existing deep learning based methods learn the visual representation for food classification based on human annotation of each food image. However, most food images captured from real life are obtained without labels, requiring human annotation to train deep learning based methods. This approach is not feasible for real world deployment due to high costs. To make use of the vast amount of unlabeled images, many existing works focus on unsupervised or self-supervised learning to learn the visual representation directly from unlabeled data. However, none of these existing works focuses on food images, which is more challenging than general objects due to its high inter-class similarity and intra-class variance. In this paper, we focus on two items: the comparison of existing models and the development of an effective self-supervised learning model for food image classification. Specifically, we first compare the performance of existing state-of-the-art self-supervised learning models, including SimSiam, SimCLR, SwAV, BYOL, MoCo, and Rotation Pretext Task on food images. The experiments are conducted on the Food-101 dataset, which contains 101 different classes of foods with 1,000 images in each class. Next, we analyze the unique features of each model and compare their performance on food images to identify the key factors in each model that can help improve the accuracy. Finally, we propose a new model for unsupervised visual representation learning on food images for the classification task.