A simple and effective semi-supervised learning framework for hyperspectral image classification

In this paper, we propose a novel semi-supervised learning classification framework using box-based smooth ordering and multiple 1D-embedding-based interpolation (M1DEI) in [J. Wang, Semi-supervised learning using multiple one-dimensional embedding-based adaptive interpolation, Int. J. Wavelets Multiresolut. Inf. Process. 14(2) (2016) 11 pp.] for hyperspectral images. Due to the lack of labeled samples, conventional supervised approaches cannot generally perform efficient enough. On the other hand, obtaining labeled samples for hyperspectral image classification is difficult, expensive and time-consuming, while unlabeled samples are easily available. The proposed method can effectively overcome the lack of labeled samples by introducing new labeled samples from unlabeled samples in a label boosting framework. Furthermore, the proposed method uses spatial information from the pixels in the neighborhood of the current pixel to better catch the features of hyperspectral image. The proposed idea is that, first, we extract the box (cube data) of each pixel from its neighborhood, then apply multiple 1D interpolation to construct the classifier. Experimental results on three hyperspectral data sets demonstrate that the proposed method is efficient, and outperforms recent popular semi-supervised methods in terms of accuracies.

To build small and efficient neural networks for hyperspectral image (HSI) classification, this letter presents a depthwise separable residual neural network (ResNet). This approach, motivated by the popular MobileNet architecture, decomposes the traditional spatial-spectral convolution operation into a spatial-independent pointwise spectral convolution and a spectral-independent depthwise spatial convolution. It allows the separation of spectral and spatial information in HSI and also greatly reduces the network size to prevent the overfitting issue. To better preserve the class boundaries and edges, the proposed ResNet is integrated into a maximum a posteriori (MAP) framework to allow the use of the conditional random field (CRF) model. The experiment results on benchmark HSI scene demonstrate that the proposed ResNet compares favorably with several popular deep learning HSI classifiers and that the ResNet-CRF approach achieves higher accuracy and better boundaries among neighboring classes.

Due to the 3-D nature of hyperspectral images, as well as the spatial properties (such as regularity and continuity) of land covers, many 3-D feature extraction operators have been designed to fully exploit the joint spatial–spectral information. However, the large amount of obtained features can suffer from the “curse of dimensionality” problem, especially for the small training sample set. Moreover, various spatial–spectral features can represent the characteristics of the hyperspectral image from different aspects. In this paper, a multiple 3-D feature fusion framework (M3DF3) has been proposed for hyperspectral image classification. First, we extend the 2-D Gabor surface feature into 3-D (3DSF) domains to comply with the spatial–spectral structure of the hyperspectral image, which is directly applied on the original hyperspectral image instead of the Gabor features. Second, three 3-D feature extraction methods, including the 3-D morphological profile, the 3-D local binary pattern, and the proposed 3DSF, that, respectively, characterize the hyperspectral image from three different angles, i.e., morphology, local dependence, and shape smoothness, are fused under a multitask sparse representation framework to take full advantage of the multiple 3-D features together. The proposed M3DF3 approach was fully tested on three real-world hyperspectral image data, i.e., the widely used Indian Pines, Pavia University, and Houston University. The results show that our method can achieve as high as 68.22%, 79.44%, and 72.84% accuracies, respectively, even when only few samples, i.e., three samples per class, are used for training.

Hyperspectral image (HSI) clustering has been widely used in the field of remote sensing. However, most traditional clustering algorithms are not suitable for dealing with large-scale HSI due to their low clustering performance and high computational complexity. In this letter, we propose a novel fuzzy clustering algorithm, called fuzzy embedded clustering based on the bipartite graph (FECBG), to efficiently deal with large-scale HSI clustering problems. First, we propose the FECBG method that incorporates fuzzy clustering with the nonnegative regularization term based on the bipartite graph into a unified model, which has good clustering performance and reduces the sensitivity of fuzzy clustering to the initial cluster centers. Second, we adopt the fast spectral embedded method to obtain the low-dimensional representation of HSI data, to reduce the computational complexity. At last, we add the nonnegative regularization term based on the bipartite graph to fuzzy clustering, to constrain the solution space of the fuzzy membership matrix. Experimental results on several HSI data sets have demonstrated the efficiency and effectiveness of the proposed FECBG algorithm.

During recent years, convolutional neural network (CNN)-based methods have been widely applied to hyperspectral image (HSI) classification by mostly mining the spectral variabilities. However, the spatial consistency in HSI is rarely discussed except as an extra convolutional channel. Very recently, the development of pixel pair features (PPF) for HSI classification offers a new way of incorporating spatial information. In this paper, we first propose an improved PPF-style feature, the spatial pixel pair feature (SPPF), that better exploits both the spatial/contextual information and spectral information. On top of the new SPPF, we further propose a flexible multi-stream CNN-based classification framework that is compatible with multiple in-stream sub-network designs. The proposed SPPF is different from the original PPF in its paring pixel selection strategy: only pixels immediately adjacent to the central one are eligible, therefore imposing stronger spatial regularization. Additionally, with off-the-shelf classification sub-network designs, the proposed multi-stream, late-fusion CNN-based framework outperforms competing ones without requiring extensive network configuration tuning. Experimental results on three publicly available datasets demonstrate the performance of the proposed SPPF-based HSI classification framework.

Context. The problem of clustering (classification without a teacher) is often occures when processing data arrays of various natures, which is quite an interesting and integral part of artificial intelligence. To solve this problem, there are many known methods and algorithms based on the principles of the distribution density of observations in the analyzed data. However, these methods are rather complicated in software implementation and are not without drawbacks, namely: the problem of determining significant clusters in datasets of different densities, multiepoch self-learning, getting stuck in local extrema of goal functions, etc. It should be noted that the methods based on the analysis of the peaks of the data distribution density are clear in nature, therefore, to expand the capabilities of these methods, it is advisable to introduce their fuzzy modification. Objective. The aim of the work is to introduce fast fuzzy data clustering using density peaks distribution of the datasets, that can find the prototypes (centroids) of clusters that overlapping regardless of the amount of incoming data. Method. The problem of fuzzy clustering data arrays based on a hybrid method that based on the simultaneous use of a credibilistic approach to fuzzy clustering and an algorithm for finding the types of distribution density of the initial data is proposed. A feature of the proposed method is computational simplicity and high speed, due to the fact that the entire array is processed only once, that is, eliminates the need for multi-era self-learning, implemented in traditional fuzzy clustering algorithms. Results. A feature of the proposed method of fast fuzzy credibilistic clustering using of density peaks distribution is characterized by computational simplicity and high speed due to the fact that the entire array is processed only once, that is, the need for multiepoch self-learning is eliminated, which is implemented in traditional fuzzy clustering algorithms. The results of the computational experiment confirm the effectiveness of the proposed approach in clustering problems under conditions in the case when the clusters are ovelap. Conclusions. The experimental results allow us to recommend the developed method for solving the problems of automatic clustering and data classification, as quickly as possible to find the centroids of clusters. The proposed method of fast fuzzy credibilistic clustering using of density peaks distribution of dataset is intended for use in computational intelligence systems, neuro-fuzzy systems, in training artificial neural networks and in clustering problems.

Combining spectral and spatial information can significantly improve the classification performance of hyperspectral image (HSI). Currently, a lot of spectral–spatial HSI classification methods have been proposed. However, the task of HSI classification has remained challenging since the number of training samples is limited in real scenarios. In this article, we propose a novel HSI classification framework with single sample, in which the spectral self-similarity and spatial polygon structure information are fully combined to improve the classification performance. On the one hand, spectral self-similarity is used to expand training samples, which makes it possible to obtain sufficient samples with minimal cost. On the other hand, polygonal partition is introduced to acquire the geometrical structure of land covers in man-made environments. Specifically, the edge information of geometric objects is captured by polygonal partition, which can be utilized to constrain the spatial range of sample expansion and optimize the classification results. Experimental results on three real HSIs illustrate that the proposed method performs very well under small training sample size even when the number of samples is single per class.

Deep learning technologies have been successfully applied to hyperspectral (HS) image classification with remarkable performance. However, compared with traditional machine learning methods, neural networks usually need more data. In remote sensing (RS) research, obtaining a large number of labeled HS data is very difficult and expensive work. Simultaneously, the distribution of feature information is bound to be unbalanced, and tends to conform to the long tail. At present, the neighborhood information of unlabeled samples is usually ignored in HS image classification tasks based on semi-supervised learning. In this letter, we propose a new semi-supervised long-tail learning framework based on spatial neighborhood information (SLN-SNI), which can complete the HS image classification task under unbalanced small sample data. Specifically, a new semi-supervised learning strategy is proposed. On this basis, a new method to determine the label of unlabeled samples based on spatial neighborhood information (SNI) is proposed. The coarse classification results divided into three situations are judged again, and the accuracy of pseudo labels is improved. The performance of the proposed method is tested on three public HS image datasets. Compared with the current advanced methods have achieved a certain improvement.

Hyperspectral image classification plays a key role in accurately identifying land cover, but still faces challenges such as mixed pixels, spectral heterogeneity, and multi-scale fusion. Existing methods remain limited in frequency-domain feature extraction, cross-modal interaction, and multi-scale information integration. To address these issues, this paper proposes FDSNet, a model that fuses frequency- and spatial-domain features to enhance classification performance. In the spatial stream, a dual-path encoding mechanism extracts frequency and spatial features, while cross-cooperative attention further captures spatial context. In the spectral stream, a cross-scale interaction pyramid strengthens multi-scale spectral representations, combined with dynamic convolution and spectral–spatial attention to refine feature learning. Finally, an improved cross-modal interaction module achieves efficient fusion of spectral and spatial features. Experiments on the PU dataset show that the proposed method outperforms existing approaches in overall accuracy (OA), average accuracy (AA), and the Kappa coefficient, demonstrating superior effectiveness and robustness.

A Binary Grey Wolf Optimization based Hybrid Convolutional Neural Network (BGWOHCNN) framework for hyperspectral image classification

Hyperspectral image (HSI) classification methods based on deep learning techniques have succeeded wildly. However, the high-dimensional non-linearity, spectral mixing, and difficulty in labeling training samples of HSI still hinder the accuracy of HSI classification. Several patch-free-based methods were proposed for HSI classification and have attracted attention. Nevertheless, recent patch-free methods have focused on low- or high-order interactions, ignoring the abundant middle-order interactions, failing to capture the multi-order interactions in the context of HSI, and difficulty extracting discriminative features when the sample data is imbalanced. In this paper, a combining multi-attention and asymmetric convolution (CMAAC) global learning framework was proposed for insufficient utilization of spectral-spatial information and imbalanced HSI samples. In CMAAC, the channel convolutional long short-term mechanism and multi-order spatial aggregation block (CLMS), which aim to capture multi-order interactions information and extract more discriminant spectral-spatial features effectively, is proposed. The pyramid-enhanced attention mechanism (PEAM) alleviates the information loss in feature flow, retains more spatial information, and better solves the challenge of scale diversity in different land-cover types. The asymmetric convolutional structure (ACS) at the end of the model highlights the influence of local key feature points and improves its representation ability. Additionally, the framework introduces a joint loss function to reduce misclassified classes caused by the imbalance between well-classified and hard-classified samples. We conducted experiments on four benchmark datasets and compared them with the state-of-the-art approaches, demonstrating the model’s effectiveness and superiority.

A spatial-spectral metric learning (SSML) framework for hyperspectral image (HSI) classification is proposed. SSML learns a metric by considering both the spectral characteristics and spatial features represented as the mean of neighboring pixels. It first performs the local pixel neighborhood preserving embedding (LPNPE) to reduce the dimensionality of HSI and meanwhile to preserve the spatial local similarity structure. Then, it learns a spectral and spatial distance metric, separately. Finally, the combination of the spectral and spatial metrics yields a joint spatial-spectral metric. It is followed by a nearest neighbor (NN) classifier for HSI classification. SSML shows good performance over the spectral and spatial NN and SVM on the benchmark hyperspectral data set of Indian Pines.

A hyperspectral image classification framework and its application

The Local Government of Gunungkidul creates some formulation in an effort to alleviate poverty. Indicators of poverty used are an integration of national standard indicators with consideration of locality in Gunungkidul. The Local Government of Gunungkidul uses a simple data classification, that is weighting indicators in the grouping of data poverty in data classification of, so it still frequently goes wrong and requires a long time. Therefore, this study aims to perform the data clustering of poverty to determine the appropriate algorithm between FCM algorithm and K - Means with the calculation of poverty indicators in Girijati Village, Purwosari , Gunungkidul , Yogyakarta. Data domain of this study is poverty data with 15 indicators that will produce 3 cluster. Before clustering the data, first performed pretreatment includes data cleaning and data transformation. Calculation of clustering, according 3 poverty criterias in Gunungkidul, done after the data is ready. The result of the calculation is then used to compare the FCM algorithm with K - Means. Based on the analysis of the clustering result of FCM algorithm and K- Means, it shows that time and iteration of FCM algorithm relatively much more than the K-Means algorithm. In addition, the FCM algorithm is more difficult applied to more varied data , unlike the K-Means algorithm that can be applied to data with less variation. The suitability of data between FCM algorithm and the calculation of poverty indicators in the Girijati village is 50 % and for the K - Means algorithm is 83.33 % . Therefore, K- Means algorithm is more appropriately used in data classification of poverty based on the three criteria of poverty, beside FCM algorithm. So, for poverty data domain , more appropriate algorithm used for poverty data domain are K-Means algorithm.

Pixel classification among overlapping land cover regions in remote sensing imagery is a challenging task. Detection of uncertainty and vagueness are always key features for classifying mixed pixels. This chapter proposes an approach for pixel classification using hybrid approach of Fuzzy C-Means and Particle Swarm Optimization methods. This new unsupervised algorithm is able to identify clusters utilizing particle swarm optimization based on fuzzy membership values. This approach addresses overlapping regions in remote sensing images by uncertainties using fuzzy set membership values. PSO is a population-based stochastic optimization technique inspired from the social behavior of bird flocks. The authors demonstrate the algorithm for segmenting a LANDSAT image of Shanghai. The newly developed algorithm is compared with FCM and K-Means algorithms. The new algorithm-generated clustered regions are verified with the available ground truth knowledge. The validity and statistical analysis are performed to demonstrate the superior performance of the new algorithm with K-Means and FCM algorithms.