CPL-PL: Contrapositive Learning-Based Pseudo-Labeling for Semi-Supervised Scene Classification in Remote Sensing Images

Scene classification in remote sensing (RS) images is a challenging task due to the limited availability of labeled data and the high intraclass variability in complex landscapes. Semi-supervised learning (SSL) has emerged as an effective approach to leverage the limited labeled data in utilizing a large amount of unlabeled data for improved classification. Pseudo-labeling (PL), a widely used SSL technique, determines suitable labels to unlabeled data based on high-confidence model predictions. However, traditional PL methods suffer from confirmation bias, where incorrect labels reinforce errors, degrading model performance. To address this, we propose contrapositive learning-based PL (CPL-PL), a novel method designed specifically for RS scene classification. CPL-PL introduces a contrapositive loss (CPLoss) that enforces feature consistency for similar scenes while ensuring representation separation for dissimilar ones, leading to more reliable pseudo-label assignments. Our approach mitigates pseudo-label noise, enhances feature discrimination, and improves classification robustness. Experimental results on benchmark RS datasets demonstrate that CPL-PL significantly outperforms conventional PL strategies, especially in low-label regimes. The proposed method provides a promising direction for advancing semi-supervised scene classification in RS images.