Detecting small objects in remote sensing images is a significant challenge due to their weak texture, scale variations, and dense spatial arrangements. Existing approaches often overlook the importance of prior contextual information and the aggregation of features in densely packed small objects, both of which are crucial for improving the performance of remote sensing small object detection (RSSOD). In this work, we propose the Prior Guided Context Fusion Network (PGCFNet), which enhances small object detection by decoupling scene contextual information through three novel components: the Prior Guided Context Fusion Module (PGCFM), the DepthWise Aggregator (DWA), and the Prior Guided Small Object Detector (PGSOD). This architecture facilitates a deeper exploration of the relationships between small objects and their surrounding environment. Specifically, PGCFM improves feature representation by integrating multi-scale features and applying prior-guided dynamic channel weighting, addressing the challenge of weak textures. Additionally, DWA refines feature aggregation using dilated convolutions and dynamic feature adjustment, enabling precise multi-scale detection in environments with dense small objects. Furthermore, PGSOD leverages prior knowledge to reduce background interference, enhancing small object detection across varying scales and orientations. Collectively, these modules work synergistically to advance small object detection in remote sensing images, overcoming key challenges in complex environments. Extensive experiments on three public datasets demonstrate that the performance of the proposed method outperforms several state-of-the-art detectors, especially for tiny object detection. Specifically, PGCFNet achieves 86.0% mAP on the DIOR dataset, 95.59% mAP on the NWPU VHR-10 dataset, and 58.5% mAP on the AI-TOD dataset. Additionally, we conducted generalization experiments for PGCFM, DWA and PGSOD, demonstrating its effectiveness across different datasets and detection networks with varying model sizes.

Deep neural networks (DNNs) have achieved significant advancements in hyperspectral image (HSI) classification, enabling critical applications in environmental monitoring, medical imaging, and geological analysis. However, their vulnerability to adversarial attacks, particularly in the boundary regions between classes, remains a critical challenge. Existing defense methods often struggle to address these issues due to insufficient adaptability to irregular boundary patterns and larger perturbations in boundary regions. To bridge this gap, we propose a boundary-aware network (BAN), a novel adversarial defense network framework that integrates a multiscale deformable convolution (MSDC) module with a Kolmogorov–Arnold network (KAN). The MSDC module dynamically adjusts receptive fields across scales to capture discriminative spatial-spectral features, while the KAN architecture leverages its cubic spline-based smooth nonlinearity to suppress gradient-driven adversarial perturbations. By leveraging these components, BAN not only mitigates boundary-specific vulnerabilities but also enhances global robustness against diverse adversarial threats. Experimental results on three benchmark HSI datasets demonstrate that BAN outperforms state-of-the-art methods, maintaining high accuracy and robustness under various adversarial attack scenarios.

As an effective unsupervised learning method, contrastive learning (CL) has made remarkable progress in the hyperspectral image (HSI) classification. The core idea of CL is to learn representations by attracting positive samples and repelling negative samples. However, due to the patch sampling mode of HSI, the patches with the same semantic information might be undesirably considered as negative samples of each other, which are called “noisy negatives.” The noisy negatives deteriorate the performance of CL. To address the issue, a progressive CL based on noisy negatives cleaning (ProCoL) is proposed for HSI classification. In contrast to existing CL, an adjunct low-dimensional subspace is introduced. Additionally, encoder training was conceptually divided into two stages each with distinct roles. In the rough-training stage, CL is applied concurrently within two different dimensional subspaces to improve the discriminative ability of the encoder. Subsequently, as the training stabilizes, noisy negatives are gradually eliminated in the retraining stage based on the dynamically generated pseudo labels in the low-dimensional space, which further improves the latent representations of the encoder. Experiments show that the ProCoL achieves the best performance compared to the previous state-of-the-art methods.

Contrastive learning has emerged as a promising technique for hyperspectral image (HSI) classification. However, the inherent limitation of sliding window sampling in HSI results in partial samples within a mini-batch exhibiting extremely high similarity. Consequently, there is an increased number of negative sample pairs composed of similar samples, significantly reducing the effectiveness of contrastive learning. Moreover, prevailing classification models heavily depend on convolutional operations, emphasizing the extraction of local features but struggle to capture long-distance dependencies in both spatial and spectral dimensions. To address these problems and fully leverage the abundance of unlabeled samples, we propose a novel purified contrastive learning (PCL) framework for HSI classification. We design a complementary spatial-spectral representation encoder architecture that combines Convolutional Neural Network (CNN) and Transformer to capture local features and global dependencies. More importantly, a purified contrastive loss function is proposed based on super-pixel spatial prior. Extensive experiments on three public datasets demonstrate the superiority of PCL over state-of-the-art methods in HSI classification. The code for this work is available at https://github.com/zhaolin6/PCL for the sake of reproducibility.

Change detection (CD), aims to detect the changing area of the same scene at different times, which is an important application of remote sensing images. As the key data source of CD, hyperspectral image (HSI) is widely used in CD technology because of its rich spectral-spatial information. However, how to mine the multi-level spatial information of dual-temporal hyperspectral images (HSIs) and focus on the features of the pixels to be classified individually remains a problem in the spatial attention mechanism (SAM). To make full use of the spectral-spatial information of HSIs, in this paper we propose a CNN framework with compact band weighting and multi-scale spatial attention (CBW-MSSANet) for HSI pixel-level CD. The main contributions of this article are as follows: 1) a new method of pseudo-label training sample selection based on k-means (KM) centroid distance is designed; 2) apply the compact band weighting (CBW) module to HSI CD to take full advantage of the spectral information of HSIs; 3) a multi-scale spatial attention (MSSA) module is developed for pixel-level CD, which can mine multi-level spatial information and pay more attention to the features of the pixels to be classified, and combine the spatial information of adjacent pixels to make it more conducive to pixel-level CD. Experimental results on four real HSI datasets demonstrated that the performance of MSSA surpasses the classical single-scale SAM, and CBW-MSSANet is superior to some representative CD methods.

The transformer framework has shown great potential in the field of hyperspectral image (HSI) classification due to its superior global modeling capabilities compared to convolutional neural networks (CNNs). To utilize the transformer to model spatial–spectral information, a hybrid transformer that integrates multigranularity tokens and spatial–spectral attention (SSA) is proposed. Specifically, a token generator is designed to embed the multigranularity semantic tokens, which contributes richer image features to the model by exploiting CNN’s local representation capability. Moreover, a transformer encoder with an SSA mechanism is proposed to capture the global dependencies between different tokens, enabling the model to focus on more differentiated channels and spatial locations to improve the classification accuracy. Ultimately, adaptive weighted fusion is applied to different granularity transformer branches to boost HybridFormer’s classification performance. Experiments were conducted on four new challenging datasets, and the results indicate that HybridFormer achieves state-of-the-art results in terms of classification performance. The code of this work will be available athttps://github.com/zhaolin6/HybridFormerfor the sake of reproducibility.

With the increasing spectral dimension of hyperspectral images (HSI), how correctly choose bands based on band correlation and information has become more significant, but also complicated. Band selection is a combinatorial optimization problem, and intelligent optimization algorithms have been shown to be crucial in solving combinatorial optimization problems. However, major of them only use a single objective as the selection index, while neglecting the overall features of hyperspectral images, which may lead to inaccuracy in object detection. To tackle this, we propose a band selection method based on a multi-objective cuckoo search algorithm (MOCS) when constructing a multi-objective unsupervised band selection model based on the amount of information and correlation of the bands (MOCS-BS). Specifically, an adaptive strategy based on population crowding degree is first proposed to assist Lévy flight in overcoming the influence of the parameter constancy. Then, an information-sharing strategy based on grouping and crossover is designed to balance the search ability between global exploration and local exploitation, which can overcome the shortcomings caused by the lack of information interaction between individuals. Finally, the HSI classification experiments are performed by Random Forest and KNN classifiers based on the subset of bands selected by the proposed MOCS-BS method. The proposed method is compared with state-of-the-art algorithms including neighborhood grouping normalized matched filter (NGNMF) and multi-objective artificial bee colony with band selection (MABC-BS) on four HSI datasets. The experimental results demonstrate that MOCS-BS is more effective and robust than other methods.

Change detection approaches can detect changed areas of the same scene at different times. Hyperspectral remote-sensing images contain large amounts of spectral information at high resolution. As hyperspectral datasets become abundant, more and more change detection technologies use hyperspectral images as raw data. Hyperspectral images suffer from band redundancy. There is an urgent need to improve the directionality of change of information features. To solve these problems, in this article, we propose a CNN framework involving slow-fast band selection (SFBS) and feature fusion grouping (SFBS-FFGNET) for hyperspectral image change detection. The main contributions of this article are as follows: 1) based on slow feature analysis (SFA), an SFBS method is proposed, which selects slow and fast feature bands to better extract changed and unchanged features, to more effectively separate changed and unchanged pixels; 2) we used a difference matrix to enrich the level of change information to provide more change characteristics for change detection; and 3) an FFG method was used to generate a more discriminative feature group, and the related loss function was designed. Experimental results on multiple real hyperspectral datasets showed that SFBS can reduce the operating load on the computer and improve the accuracy of change detection, and FFG can also improve the accuracy of change detection. In summary, SFBS-FFGNET is superior to most existing change detection methods.

In hyperspectral anomaly detection, anomalies are rare targets that exhibit distinct spectral signatures from the background. Thus, anomalies are with low probabilities of occurrence in hyperspectral images. In this article, we develop a new technique for hyperspectral anomaly detection that adopts a new information theory perspective, to fully utilize the aforementioned concepts. Our goal is to transform system entropy into quantitative metrics of anomaly conspicuousness of pixels. To do so, two tasks are first completed: first, the construction of occurrence probability of pixels based on the density peak clustering algorithm, and second, the valid system definitions for pixels in specific anomaly detection problems with multiviews. Specifically, three types of systems are separately established by pixel pairs to conform to the definitions of three entropy definitions in information theory, i.e., Shannon entropy, joint entropy, and relative entropy. Then, three individual entropy-based metrics that assess the anomaly conspicuousness are defined. In addition, we design a standard deviation-based ensemble strategy for the integrated representation of the three individual metrics, which considers both logic “OR” and “AND” operations to simultaneously improve the detection rate and reduce the false alarm rate. Our experimental results obtained on two publicly available datasets with anomalies of different sizes and shapes demonstrate the superiority of our newly proposed anomaly detection method.

This letter introduces a novel spatial-spectral classification method for hyperspectral images (HSIs) based on a structural-kernel collaborative representation (SKCR), which considers one weak assumption of spatial neighborhood that of the pixels in a superpixel belong to the same class when exploiting contextual information in HSI. The proposed method consists of the following steps. First, a superpixel segmentation strategy is used to construct self-adaptive regions for the HSI. Then, the structural information within each superpixel block is extracted based on the density peak and K nearest neighbors. Next, dual kernels are separately utilized for the exploitation of the spectral and the spatial information. Finally, the dual kernels are combined and incorporated into a support-vector-machine classifier. Since the weak assumption of spatial neighborhood is well considered in the collaborative representation, the proposed method showed excellent classification performance for two widely used real hyperspectral data sets even when the number of training samples was relatively small.

Hyperspectral image (HSI) data have large numbers of bands that probably not all bands are equally informative and predictive for an effective HSI classification. Effective algorithms are highly desired in many real-world HSI applications, especially in cases requiring rapid learning with limited computing power. To address the abovementioned case, we present in this article a novel plug-and-play compact band weighting (CBW) module based on the attention-driven mechanism that evaluates different spectral bands according to their contributions to a given classification task. Compared to existing band weighting (BW) modules with tens of thousands of network parameters by deep learning, the proposed CBW is a lightweight module with only 20 parameters. Both model complexity and time cost are significantly reduced. The CBW module implements BW by making full use of the correlation among the adjacent spectral bands and spectral statistic information and, thereby, leads to the effect of recalibrated HSI. The experimental study has been conducted on three widely used HSI data sets, and results show the superiority of the proposed algorithm over current state-of-the-art methods of BW. The source code is available athttps://github.com/JarvenYi/CBW.

Recently, feature extraction-based methods have received increasing attention in the hyperspectral image. In this letter, to ensure a more powerful discriminative ability of extracted features, a dual-stage construction of probability (DSCP) method is proposed for hyperspectral image classification. Specifically, the extended multi-attribute profiles (EMAP) method is applied to extract the shape feature of hyperspectral remote sensing image (HSI) to obtain a more accurate initial probability map. Considering that there are still some noises in the boundaries of the initial probability map, an effective edge-preserving filter-based approach named rolling guidance filter is used for probability post-optimization. Consequently, the class label of each pixel can be determined according to the optimized probability maps. Experiments demonstrate significantly the efficiency of the proposed method in comparison with other advanced methods.

The clustering methods have a good application in many aspects, in which the density peak (DP) clustering can effectively cluster similar neighboring pixels so that the features can be extracted well for hyperspectral images (HSIs) classification. In this work, a DP based covariance matrix (DPCM) method is proposed for the feature extraction of HSIs, which not only can effectively extract features but also can reduce the within-class variations and the between-class interference. The proposed method consists of the following steps: First, maximum noise fraction is employed on the original HSI to reduce the computational complexity and eliminate noise. Second, the local densities of the sample are calculated by the DP clustering. Therefore, a reconstructed image can be obtained in which each pixel has a density feature vector. Then, the covariance matrix between each density pixel in the density map is calculated. Last, the extracted covariance matrices are fed back to the support vector machine based on the logarithm Euclidean kernel for label assignment. Experiments are conducted on the Indian pine data set, in which each of the five randomly selected marker data are selected as the training sample. The experimental results show that the method can effectively improve the classification accuracy and is superior to other classification methods.

Moving foreground objects detection in complex scenes is a tough job because it requires high recognition accuracy. Adaptive Gaussian mixture model (AGMM) can be used to extract the foreground objects and it shows good performance, however, the detection quality of the foreground objects under complex scenes is not excellent. In this paper, an AGMM and BP neural network hybrid method is proposed, which is used to extract the foreground objects in complex scenes such as, dynamic backgrounds, illumination changes and moving shadows. In this method, an improved BP neural network is used to post-process the images of the foreground objects that are extracted from the AGMM. The neural network has strong robustness by learning the statistical features of the images. Momentum term and adaptive learning rate are added in the BP neural network algorithm to improve the training speed and robustness of the network. The experimental results show that the proposed AGMM and BP neural network hybrid method can extract the complete foreground objects effectively when compared with some other moving objects detection algorithms.

Mislabeled training samples may have a negative effect on the performance of hyperspectral image classification. In order to solve this problem, a new density peak (DP) clustering-based noisy label detection method is proposed, which consists of the following steps. First, the distances among the training samples of each class are calculated using four representative distance metrics, i.e., the Euclidean distance (ED), orthogonal projection divergence (OPD), spectral information divergence (SID), and correlation coefficient (CC). Then, the local density of each training sample can be obtained using the DP clustering algorithm. Finally, a local density-based decision function is used to detect the noisy labels. The effectiveness of the proposed method is evaluated using the support vector machines on several real hyperspectral data sets. Experimental results demonstrate that the proposed noisy label detection method indeed helps in improving the classification performance.

Background modeling in complex scenes is a challenging problem. In this paper, a novel background subtraction method is proposed to address it. First, the textures are modeled with local compact binary patterns (LCBP), which have excellent robustness, strong discriminative power, and fast computation speed. To make LCBP more effective to appearance changes in complex scenarios, spatiotemporal local compact binary patterns (STLCBP) are then considered in which spatial texture information and temporal motion information are combined together. Multiple color spaces are also presented to separate foreground pixels more accurately from the background. To our knowledge, this is the first time that LCBP have been used for background modeling. Extensive experimental results on a widely used dataset clearly show that the proposed method outperforms other state-of-the-art methods and works effectively in complex scenes.

General machine vision algorithms are difficult to detect LCD sub-pixel level defects. By studying the LCD screen images, we found that the pixels in the LCD screen are regularly arranged. The spectrum distribution of LCD images, which is obtained by the Fourier transform, is relatively consistent. According to this feature, a method of sub-pixel defect detection based on notch filter and image registration is proposed. First, we take a defect-free template image to establish registration template and notch-filtering template; then we take the defect images for image registration with registration template, and solve the offset problem. After the notch-filter template filtering the background texture, the defect is more obvious; Finally the defects are obtained by the threshold segmentation method. The experiment results show that the proposed method can detect sub-pixel defects accurately and quickly.

The joint sparse representation (JSR)-based classifier assumes that pixels in a local window can be jointly and sparsely represented by a dictionary constructed by the training samples. The class label of each pixel can be decided according to the representation residual. However, once the local window of each pixel includes pixels from different classes, the performance of the JSR classifier may be seriously decreased. Since correlation coefficient (CC) is able to measure the spectral similarity among different pixels efficiently, this letter proposes a new classification method via fusing CC and JSR, which attempts to use the within-class similarity between training and test samples while decreasing the between-class interference. First, the CCs among the training and test samples are calculated. Then, the JSR-based classifier is used to obtain the representation residuals of different pixels. Finally, a regularization parameter λ is introduced to achieve the balance between the JSR and the CC. Experimental results obtained on the Indian Pines data set demonstrate the competitive performance of the proposed approach with respect to other widely used classifiers.

To improve the rate stability and make a balance for different viewpoints in distributed multi-view video coding (DMVC) system, a novel symmetric DMVC (SDMVC) scheme is proposed in this paper. In the proposed scheme, every frame from all views adopts the same encoding mode and stable output rates are achieved, which are significant to improve the transmission efficiency in the channel. Both temporal and spatial correlations are exploited, in addition, a novel side information (SI) generation algorithm aiming at better exploring the correlations of proposed scheme has been proposed to obtain better performance. The simulation results show that the proposed SDMVC scheme gets a much more stable rate than the asymmetric scheme, only with neglectable bit-rate increasing. Meanwhile, the proposed SI generation algorithm significantly improves the coding performance.