Reconstruction-Contrast Coupling Learning for Open-Set Semi-Supervised Hyperspectral Image Classification.

Abstract

Although numerous semi-supervised learning methods have been elaborately designed for hyperspectral image (HSI) classification, most existing semi-supervised learning paradigms still rely on a closed-set assumption. These methods implicitly assume that the category spaces of labeled and unlabeled samples are completely aligned, that is, all unlabeled samples must belong to a pre-defined known category set. However, the closed-set assumption is particularly problematic in practical remote sensing scenarios because partial unlabeled data inevitably belong to unknown categories. To address this challenge, this paper proposes a reconstruction-contrast coupling learning (ReCo²L) method for open-set semi-supervised HSI classification, fully leveraging the complementarity between masked feature reconstruction learning and contrastive learning to enhance the encoder's local detail sensitivity and global discriminative ability. Specifically, we first apply a masked feature reconstruction learning with an adaptive masking strategy to enhance the encoder's ability to capture local details by high-quality spectral-spatial feature reconstruction. Then, we employ contrastive learning to strengthen the encoder's capability to extract global characteristics by pulling semantically similar samples closer and pushing dissimilar ones farther apart in the feature space. Finally, a pixel-prototype deviation loss is proposed to further improve both inter-category distinguishability and intra-category compactness by reducing the distances between labeled sample features and their corresponding class anchors. Extensive experiments on three benchmark datasets demonstrate that our proposed ReCo²L achieves superior classification performance in both known and unknown categories and significantly surpasses 10 state-of-the-art HSI classification methods. The code will be available at https://github.com/repository-AI-chen/ReCo2L.