LGFormer: Local-to-Global Transformer for Hyperspectral Image Classification

Recently, many transformer-based approaches have emerged in the field of hyperspectral image (HSI) classification. However, existing transformer-based works either model the information of spectral vectors using a transformer or introduce a vision transformer (ViT) for feature expression of the spatial patch after principal component analysis (PCA), neglecting the spectral-spatial correlation of HSI. Besides, local details and global distributions are always challenging to simultaneously extract in these methods. To address the above issues, a local-to-global transformer (LGFormer) is proposed in this paper. In detail, the proposed approach directly extracts inherent features on the originally spectral-spatial patch, which not only takes the spatial distribution and spectral continuity into account but also preserves the intrinsically spectral-spatial correlation of the HSI cube. Moreover, a local-to-global self-attention (LGSA) including 3-D convolutional neural network (CNN) and ViT is designed in the presented LGFormer. With the above HSI-tailored structure, both fine- and coarse-grained features can be captured by progressively spectral-spatial feature learning. Experimental results on benchmark HSI datasets demonstrate that the proposed LGFormer can outperform other methods in terms of higher accuracy and finer classification maps.