Super-resolution (SR) technology plays a crucial role in improving the spatial resolution of remote sensing images so as to overcome the physical limitations of spaceborne imaging systems. Although deep convolutional neural networks have achieved promising results, most of them overlook the advantage of self-similarity information across different scales and high-dimensional features after the upsampling layers. To address the problem, we propose a hybrid-scale hierarchical transformer network (HSTNet) to achieve faithful remote sensing image SR. Specifically, we propose a hybrid-scale feature exploitation module to leverage the internal recursive information in single and cross scales within the images. To fully leverage the high-dimensional features and enhance discrimination, we designed a cross-scale enhancement transformer to capture long-range dependencies and efficiently calculate the relevance between high-dimension and low-dimension features. The proposed HSTNet achieves the best result in PSNR and SSIM with the UCMecred dataset and AID dataset. Comparative experiments demonstrate the effectiveness of the proposed methods and prove that the HSTNet outperforms the state-of-the-art competitors both in quantitative and qualitative evaluations.

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Images captured in a low-light environment are strongly influenced by noise and low contrast, which is detrimental to tasks such as image recognition and object detection. Retinex-based approaches have been continuously explored for low-light enhancement. Nevertheless, Retinex decomposition is a highly ill-posed problem. The estimation of the decomposed components should be combined with proper constraints. Meanwhile, the noise mixed in the low-light image causes unpleasant visual effects. To address these problems, we propose a Constraint Low-Rank Approximation Retinex model (CLAR). In this model, two exponential relative total variation constraints were imposed to ensure that the illumination is piece-wise smooth and that the reflectance component is piece-wise continuous. In addition, the low-rank prior was introduced to suppress the noise in the reflectance component. With a tailored separated alternating direction method of multipliers (ADMM) algorithm, the illumination and reflectance components were updated accurately. Experimental results on several public datasets verify the effectiveness of the proposed model subjectively and objectively.

Medical imaging technology plays a crucial role in the diagnosis and treatment of diseases. However, the captured medical images are often in a low resolution (LR) due to the limited imaging condition. Super-resolution (SR) technology is a feasible solution to enhance the resolution of a medical image without increasing the hardware cost. However, the existing SR methods often ignore high-frequency details, which results in blurred edges and an unsatisfying visual perception. In this paper, a gated multi-attention feedback network (GAMA) is proposed for medical image SR. Specifically, a gated multi-feedback network is employed as the backbone to extract hierarchical features. Meanwhile, a layer attention feature extraction (LAFE) module is introduced to refine the feature map. In addition, a channel-space attention reconstruction (CSAR) module is built to enhance the representational ability of the semantic feature map. Furthermore, a gradient variance loss is tailored as the regularization in guiding the model learning to regularize the model in generating a faithful high-resolution image with rich textures and sharp edges. The experiments verify the effectiveness of the proposed GAMA compared with the state-of-the-art approaches.

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