Adaptive Sparse Self-Attention for Efficient Image Super-Resolution and Beyond

Benefiting from the effectiveness of the self-attention mechanisms in the Transformer framework for modeling non-local features of images, significant progress has been achieved in image super-resolution. We note that existing self-attention mechanisms usually explore all similarities of the tokens between the queries and keys for the feature aggregation. However, using all the similarities does not effectively facilitate the high-quality image reconstruction as not all the tokens from the queries are relevant to those in keys. We further note that self-attention mechanisms are less effective for local feature exploration, which are less effective for the structural detail restoration. To overcome these problems, we develop a simple yet effective adaptive sparse self-attention method to utilize the most useful information of tokens for image restoration. We first develop a local spatial-variant feature estimation method to build the query and key used in the self-attention so that local information can be better modeled. Then, we present a simple yet effective sparse self-attention to adaptively select the most useful similarity values from the self-attention matrix for better the feature aggregation. We analyze that the proposed method models both local and non-local features and thus facilitates better structural detail restoration. We further show that the proposed method can serve as an alternative to existing self-attention mechanisms for better image restoration. Experimental results show that the proposed method performs favorably against state-of-the-art ones on benchmark datasets in terms of accuracy and model complexity.