Underwater images often exhibit poor quality, imbalanced coloration, and low
contrast due to the complex and intricate interaction of light, water, and
objects. Despite the significant contributions of previous underwater
enhancement techniques, there exist several problems that demand further
improvement: (i) Current deep learning methodologies depend on Convolutional
Neural Networks (CNNs) that lack multi-scale enhancement and also have limited
global perception fields. (ii) The scarcity of paired real-world underwater
datasets poses a considerable challenge, and the utilization of synthetic image
pairs risks overfitting. To address the aforementioned issues, this paper
presents a Multi-scale Transformer-based Network called UWFormer for enhancing
images at multiple frequencies via semi-supervised learning, in which we
propose a Nonlinear Frequency-aware Attention mechanism and a Multi-Scale
Fusion Feed-forward Network for low-frequency enhancement. Additionally, we
introduce a specialized underwater semi-supervised training strategy, proposing
a Subaqueous Perceptual Loss function to generate reliable pseudo labels.
Experiments using full-reference and non-reference underwater benchmarks
demonstrate that our method outperforms state-of-the-art methods in terms of
both quantity and visual quality.

该研究通过使用多尺度转换网络和半监督学习，提出了一种用于增强多频率图像的方法，通过非线性频率感知注意机制和多尺度融合前馈网络进行低频增强。此外，还引入了一种专门的水下半监督训练策略，提出了一个水下感知损失函数以生成可靠的伪标签，实验证明该方法在数量和视觉质量方面优于现有的水下图像增强方法。