How Powerful Potential of Attention on Image Restoration?
Cong Wang Jinshan Pan Yeying Jin Liyan Wang Wei Wang Gang Fu Wenqi Ren Xiaochun Cao
Transformers have demonstrated their effectiveness in image restoration
tasks. Existing Transformer architectures typically comprise two essential
components: multi-head self-attention and feed-forward network (FFN). The
former captures long-range pixel dependencies, while the latter enables the
model to learn complex patterns and relationships in the data. Previous studies
have demonstrated that FFNs are key-value memories \cite{geva2020transformer},
which are vital in modern Transformer architectures. In this paper, we conduct
an empirical study to explore the potential of attention mechanisms without
using FFN and provide novel structures to demonstrate that removing FFN is
flexible for image restoration. Specifically, we propose Continuous Scaling
Attention (\textbf{CSAttn}), a method that computes attention continuously in
three stages without using FFN. To achieve competitive performance, we propose
a series of key components within the attention. Our designs provide a closer
look at the attention mechanism and reveal that some simple operations can
significantly affect the model performance. We apply our \textbf{CSAttn} to
several image restoration tasks and show that our model can outperform
CNN-based and Transformer-based image restoration approaches.