Mixed noise pollution in HSI severely disturbs subsequent interpretations and applications. In this technical review, we first give the noise analysis in different noisy HSIs and conclude crucial points for programming HSI denoising algorithms. Then, a general HSI restoration model is formulated for optimization. Later, we comprehensively review existing HSI denoising methods, from model-driven strategy (nonlocal mean, total variation, sparse representation, low-rank matrix approximation, and low-rank tensor factorization), data-driven strategy 2-D convolutional neural network (CNN), 3-D CNN, hybrid, and unsupervised networks, to model-data-driven strategy. The advantages and disadvantages of each strategy for HSI denoising are summarized and contrasted. Behind this, we present an evaluation of the HSI denoising methods for various noisy HSIs in simulated and real experiments. The classification results of denoised HSIs and execution efficiency are depicted through these HSI denoising methods. Finally, prospects of future HSI denoising methods are listed in this technical review to guide the ongoing road for HSI denoising. The HSI denoising dataset could be found at https://qzhang95.github.io.

Fusing a low-resolution hyperspectral image (LrHSI) with an auxiliary high-resolution multispectral image (HrMSI) is a burgeoning technique to realize hyperspectral image super-resolution, in which learning-based methods have dominated the mainstream direction. However, the underutilization of degradation models and strong dependence on large-scale training triplets severely impedes their applicability and performance. Considering these issues, we reformulate the fusion task as a spectral mapping problem and hence propose an unsupervised model-guided coarse-to-fine fusion network. Specifically, degradation knowledge learning is first performed to fully excavate latent model information, which will serve as guidance for better mapping learning. Following that, a coarse-to-fine fusion network is constructed with a multi-scale attentional fusion module in the head and a coarse-to-fine structure in the tail. The former is deployed to achieve a more informative compression, and the latter is adopted to capture the spectral relationship, including a spectral degradation-guided subnetwork for group-by-group coarse reconstruction and a refinement subnetwork for inter-group correlation and dependencies. Finally, high-resolution HSI can be recovered via established spectral mapping. Extensive experiments on simulated and real datasets verify the superiority of our proposed method. The code is available at https://github.com/JiaxinLiCAS/UMC2FF_GRSL.

Model-driven methods and data-driven methods have been widely developed for hyperspectral image (HSI) denoising. However, there are pros and cons in both model-driven and data-driven methods. To address this issue, we develop a self-supervised HSI denoising method via integrating model-driven with data-driven strategy. The proposed framework simultaneously cooperates the spectral low-rankness prior and deep spatial prior (SLRP-DSP) for HSI self-supervised denoising. SLRP-DSP introduces the Tucker factorization via orthogonal basis and reduced factor, to capture the global spectral low-rankness prior in HSI. Besides, SLRP-DSP adopts a self-supervised way to learn the deep spatial prior. The proposed method doesn’t need a large number of clean HSIs as the label samples. Through the self-supervised learning, SLRP-DSP can adaptively adjust the deep spatial prior from self-spatial information for reduced spatial factor denoising. An alternating iterative optimization framework is developed to exploit the internal low-rankness prior of third-order tensors and the spatial feature extraction capacity of convolutional neural network. Compared with both existing model-driven methods and data-driven methods, experimental results manifest that the proposed SLRP-DSP outperforms on mixed noise removal in different noisy HSIs.

Convolutional neural networks (CNNs) have been widely used in hyperspectral image classification (HSIC). Although the current CNN-based methods have achieved good performance, they still face a series of challenges. For example, the receptive field is limited, information is lost in down-sampling layer, and a lot of computing resources are consumed for deep networks. To overcome these problems, we proposed a multilevel spectral–spatial transformer network (MSTNet) for HSIC. The structure of MSTNet is an image-based classification framework, which is efficient and straightforward. Based on this framework, we designed a self-attentive encoder. First, HSIs are processed into sequences. Meanwhile, a learned positional embedding (PE) is added to integrate spatial information. Then, a pure transformer encoder (TE) is employed to learn feature representations. Finally, the multilevel features are processed by decoders to generate the classification results in the original image size. The experimental results based on three real hyperspectral datasets demonstrate the efficiency of the proposed method in comparison with the other related CNN-based methods.

Wealthy spectral information provided by hyperspectral image (HSI) offers great benefits for many applications in hyperspectral data exploitation. However, processing such high-dimensional data volumes that may result in redundant bands due to its high interband correlation will be a challenge. For target detection and classification, this is particularly true since there may only need a relatively small number of bands that respond one particular target of interest well, while most of other bands do not. Band selection (BS) is a major dimensionality reduction technique to remove the redundant bands and selects a few bands to represent the entire image. However, how to eliminate the effect of uninteresting targets with similar spectra on detection of interesting targets is a severe issue arising in target detection for BS. This article develops a new approach called target-constrained interference-minimized BS (TCIMBS) which can be used to select band subset for specific target detection, while annihilating targets of no interest and suppressing interferers and background. Its idea is derived from target-constrained interference-minimized filter (TCIMF). By taking advantage of TCIMF, two band prioritization (BP) criteria called forward minimum variance BP (FMinV-BP) and backward maximum variance BP (BMaxV-BP) along with their three band search-based BS counterparts called sequential forward TCIMBS (SF-TCIMBS), sequential backward TCIMBS (SB-TCIMBS), and improved SB-TCIMBS (SB-TCIMBS*) are derived. The experimental results suggest that TCIMBS can improve the detection accuracy and also achieve better performance in comparison with several state-of-the-art methods.

Tensor-based methods have been widely studied to attack inverse problems in hyperspectral imaging since a hyperspectral image (HSI) cube can be naturally represented as a third-order tensor, which can perfectly retain the spatial information in the image. In this article, we extend the linear tensor method to the nonlinear tensor method and propose a nonlinear low-rank tensor unmixing algorithm to solve the generalized bilinear model (GBM). Specifically, the linear and nonlinear parts of the GBM can both be expressed as tensors. Furthermore, the low-rank structures of abundance maps and nonlinear interaction abundance maps are exploited by minimizing their nuclear norm, thus taking full advantage of the high spatial correlation in HSIs. Synthetic and real-data experiments show that the low rank of abundance maps and nonlinear interaction abundance maps exploited in our method can improve the performance of the nonlinear unmixing. A MATLAB demo of this work will be available at https://github.com/LinaZhuang for the sake of reproducibility.