CR-former: Single-Image Cloud Removal With Focused Taylor Attention
Yang Wu, Ye Deng, Sanping Zhou, Yuhan Liu, Wenli Huang, Jinjun Wang
Abstract
Cloud removal aims to restore high-quality images from cloud-contaminated captures, which is essential in remote sensing applications. Effectively modeling the long-range relationships between image features is key to achieving high-quality cloud-free images. While self-attention mechanisms excel at modeling long-distance relationships, their computational complexity scales quadratically with image resolution, limiting their applicability to high-resolution remote sensing images. Current cloud removal methods have mitigated this issue by restricting the global receptive field to smaller regions or adopting channel attention to model long-range relationships. However, these methods either compromise pixel-level long-range dependencies or lose spatial information, potentially leading to structural inconsistencies in restored images. In this work, we propose the focused Taylor attention (FT-Attention), which captures pixel-level long-range relationships without limiting the spatial extent of attention and achieves the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {O}(N)$ </tex-math></inline-formula> computational complexity, where N represents the image resolution. Specifically, we utilize Taylor series expansions to reduce the computational complexity of the attention mechanism from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {O}(N^{2})$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {O}(N)$ </tex-math></inline-formula>, enabling efficient capture of pixel relationships directly in high-resolution images. Additionally, to fully leverage the informative pixel, we develop a new normalization function for the query and key, which produces more distinguishable attention weights, enhancing focus on important features. Building on FT-Attention, we design a U-net style network, termed the CR-former, specifically for cloud removal. Extensive experimental results on representative cloud removal datasets demonstrate the superior performance of our CR-former. The code is available at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/wuyang2691/CR-former</uri>.