The OVA-classifier outputs the confidence score of a sample being an inlier, providing a threshold to detect outliers.

Semi-supervised learning (SSL) is an effective means to leverage unlabeled data to improve a model's performance. Typical SSL methods like FixMatch assume that labeled and unlabeled data share the same label space. However, in practice, unlabeled data can contain categories unseen in the labeled set, i.e., outliers, which can significantly harm the performance of SSL algorithms. To address this problem, we propose a novel Open-set Semi-Supervised Learning (OSSL) approach called OpenMatch.Learning representations of inliers while rejecting outliers is essential for the success of OSSL. To this end, OpenMatch unifies FixMatch with novelty detection based on one-vs-all (OVA) classifiers. The OVA-classifier outputs the confidence score of a sample being an inlier, providing a threshold to detect outliers. Another key contribution is an open-set soft-consistency regularization loss, which enhances the smoothness of the OVA-classifier with respect to input transformations and greatly improves outlier detection.

The OV A-classifier outputs the confidence score of a sample being an inlier, providing a threshold to detect outliers.

Semi-supervised learning (SSL) uses unlabeled data to improve the performance of machine learning models when labeled data is scarce. However, its real-world applications often face the label distribution mismatch problem, in which the unlabeled dataset includes instances whose ground-truth labels are absent from the labeled training dataset. Recent studies, referred to as safe SSL, have addressed this issue by using both classification and out-of-distribution (OOD) detection. However, the existing methods may suffer from overconfidence in deep neural networks, leading to increased SSL errors because of high confidence in incorrect pseudo-labels or OOD detection. T o address this, we propose a novel method, CaliMatch, which calibrates both the classifier and the OOD detector to foster safe SSL. CaliMatch presents adaptive label smoothing and temperature scaling, which eliminates the need to manually tune the smoothing degree for effective calibration. W e give a theoretical justification for why improving the calibration of both the classifier and the OOD detector is crucial in safe SSL. Extensive evaluations on CIF AR-10, CIF AR-100, SVHN, TinyImageNet, and ImageNet demonstrate that CaliMatch outperforms the existing methods in safe SSL tasks.

Semi-supervised learning (SSL) is an effective means to leverage unlabeled data to improve a model's performance. Typical SSL methods like FixMatch assume that labeled and unlabeled data share the same label space. However, in practice, unlabeled data can contain categories unseen in the labeled set, i.e., outliers, which can significantly harm the performance of SSL algorithms. To address this problem, we propose a novel Open-set Semi-Supervised Learning (OSSL) approach called OpenMatch.Learning representations of inliers while rejecting outliers is essential for the success of OSSL. To this end, OpenMatch unifies FixMatch with novelty detection based on one-vs-all (OVA) classifiers. The OVA-classifier outputs the confidence score of a sample being an inlier, providing a threshold to detect outliers.

Moreover, when we tackle a K-progress by propagating the label information from way classification problem with a large K, the binary detectors labeled data to unlabeled data (Berthelot et al. 2019; Xu et al. are less robust to identify outliers from such a complex 2021; Wang et al. 2022b; Zheng et al. 2022). Despite the dataset that contains multi-class information (Carbonneau success, SSL methods are deeply rooted in the closed-set assumption et al. 2018). One advanced method, evidential deep learning that labeled data, unlabeled data and test data share (EDL) (Sensoy, Kaplan, and Kandemir 2018) can explicitly the same predefined label set. In reality (Yu et al. 2020), such quantify the classification uncertainty corresponding an assumption may not always hold as we can only accurately to the unknown class, by treating the network's output as evidence control the label set of labeled data, while unlabeled for parameterizing the Dirichlet distribution according and test data may include outliers that belong to the novel to subjective logic (Jøsang 2016). Compared with Softmax classes that are not seen in labeled data.