Generalized Category Discovery

TL;DR

This paper introduces a new framework called 'Generalized Category Discovery' that effectively categorizes both known and novel classes in unlabelled image datasets using vision transformers, contrastive learning, and semi-supervised clustering.

Contribution

It extends existing methods to handle more realistic open-world recognition scenarios, proposing novel algorithms for class estimation and clustering.

Findings

Semi-supervised k-means significantly outperforms baselines

Vision transformers with contrastive learning improve recognition accuracy

Proposed class estimation method accurately determines number of classes

Abstract

In this paper, we consider a highly general image recognition setting wherein, given a labelled and unlabelled set of images, the task is to categorize all images in the unlabelled set. Here, the unlabelled images may come from labelled classes or from novel ones. Existing recognition methods are not able to deal with this setting, because they make several restrictive assumptions, such as the unlabelled instances only coming from known - or unknown - classes, and the number of unknown classes being known a-priori. We address the more unconstrained setting, naming it 'Generalized Category Discovery', and challenge all these assumptions. We first establish strong baselines by taking state-of-the-art algorithms from novel category discovery and adapting them for this task. Next, we propose the use of vision transformers with contrastive representation learning for this open-world setting. We then introduce a simple yet effective semi-supervised $k$-means method to cluster the unlabelled data into seen and unseen classes automatically, substantially outperforming the baselines. Finally, we also propose a new approach to estimate the number of classes in the unlabelled data. We thoroughly evaluate our approach on public datasets for generic object classification and on fine-grained datasets, leveraging the recent Semantic Shift Benchmark suite. Project page at https://www.robots.ox.ac.uk/~vgg/research/gcd