Currently, fusion-based hyperspectral image super-resolution (fusion-based HSI-SR) has become an efficient technology to improve the spatial resolution of hyperspectral images. However, in real scenarios, it may not be possible to obtain high-resolution multispectral images (HR-MSI) of the same temporal and region corresponding to low-resolution hyperspectral images (LR-HSI) due to the limitations of imaging conditions and environmental changes. In view of this spatial-temporal constraint, it becomes a feasible solution to regard HR-MSI, which has similar spatial structure and semantics to LR-HSI, as a reference to assist in reconstruction. Therefore, this paper proposes a Cross-Correlation & Self-Similarity Guided Texture Transfer Network (C2S2TNet), which utilizes the texture details of HR-MSI and the self-similarity information of LR-HSI to achieve reference-based hyperspectral image super-resolution. Specifically, we design a Cross-Correlation & Self-Similarity Guided Cluster-Aware Matching (C2S2CAM) strategy, which realizes multi-correspondence texture matching and feature aggregation in non-local regions based on dynamic clustering and cluster-aware graph structure, effectively alleviating the misuse and underuse of information. In addition, we also propose a Spectral-Spatial State-Space Fusion Module (S2-SSFM) based on the state-space model to perform feature fusion and enhancement in both spatial and spectral domains to ensure that the target HR-HSI maintains the spatial-spectral structural consistency with the LR-HSI. Experimental verification shows that C2S2TNet can achieve excellent performance in cross-temporal and cross-regional scenarios, confirming the effectiveness of this method. Code can be accessed at https://github.com/Jiahuiqu/C2S2TNet.

Existing fusion-based hyperspectral image super-resolution (fusion-based HSI-SR) methods usually reconstruct high-resolution hyperspectral image (HR-HSI) by integrating the complementary information of low-resolution hyperspectral image (LR-HSI) and high-resolution multispectral image (HR-MSI). However, most of such methods rely on accurately registered images or consider registration and fusion as a two-stage task, which means that fusion must tolerate the accumulation of errors due to misregistration. In this paper, we propose a progressive multi-iteration registration-fusion co-optimization network (PMI-RFCoNet) for unregistered hyperspectral image super-resolution, which progressively refines the registration and fusion result over multiple levels to reconstruct registered HR-HSI. To achieve registration-fusion co-optimization, the registration-fusion cooptimization block (Co-RFB) is designed to iterate continuously over multiple levels. We embed the interactive registration module (IRM) and the spectral recalibration and fusion module (SRFU) in Co-RFB, which can facilitate the network utilizing spatial and spectral features at different levels to generate more accurate HR-HSI. Specifically, IRM generates deformation field based on spatial correlations captured at long distances to repair non-rigid pixel offsets, and SRFU further performs adaptive high-fidelity spectral correction and spatial information fusion on the registration results. We conduct experimental verification on four widely used datasets, and the results show that PMI-RFCoNet can flexibly cope with different types and degrees of non-rigid deformation and achieve superior performance. Code is available at https://github.com/Jiahuiqu/PMI-RFCoNet.