Towards Realistic Semi-supervised Learning

Deep learning is pushing the state-of-the-art in many computer vision applications. However, it relies on large annotated data repositories, and capturing the unconstrained nature of the real-world data is yet to be solved. Semi-supervised learning (SSL) complements the annotated training data with a large corpus of unlabeled data to reduce annotation cost. The standard SSL approach assumes unlabeled data are from the same distribution as annotated data. Recently, a more realistic SSL problem, called open-world SSL, is introduced, where the unannotated data might contain samples from unknown classes. In this paper, we propose a novel pseudo-label based approach to tackle SSL in open-world setting. At the core of our method, we utilize sample uncertainty and incorporate prior knowledge about class distribution to generate reliable class-distribution-aware pseudo-labels for unlabeled data belonging to both known and unknown classes. Our extensive experimentation showcases the effectiveness of our approach on several benchmark datasets, where it substantially outperforms the existing state-of-the-art on seven diverse datasets including CIFAR-100 (similar to 17%), ImageNet100 (similar to 5%), and Tiny ImageNet (similar to 9%). We also highlight the flexibility of our approach in solving novel class discovery task, demonstrate its stability in dealing with imbalanced data, and complement our approach with a technique to estimate the number of novel classes. Code: https://github.com/nayeemrizve/TRSSL

Automated summary

Deep learning is advancing computer vision applications, but the challenge of capturing real-world data remains. Semi-supervised learning aims to reduce annotation cost by using unlabeled data. This paper introduces the concept of open-world semi-supervised learning and proposes a pseudo-label based approach that incorporates class distribution knowledge. Experimental results show significant improvement over existing state-of-the-art methods on multiple benchmark datasets.