UNet-AF: An alias-free UNet for image restoration

arXiv cs.CV / 3/13/2026

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Key Points

The authors show that standard UNet layers are prone to aliasing, which degrades translation equivariance in image restoration.
They propose UNet-AF, an alias-free UNet designed from translation-equivariant components.
Their experiments compare UNet-AF to non-equivariant baselines on image restoration tasks, reporting competitive performance with a substantial gain in equivariance.
Through extensive ablations, they demonstrate that each modification is essential for the observed empirical equivariance, and the code is available at https://github.com/jscanvic/UNet-AF

Abstract

The simplicity and effectiveness of the UNet architecture makes it ubiquitous in image restoration, image segmentation, and diffusion models. They are often assumed to be equivariant to translations, yet they traditionally consist of layers that are known to be prone to aliasing, which hinders their equivariance in practice. To overcome this limitation, we propose a new alias-free UNet designed from a careful selection of state-of-the-art translation-equivariant layers. We evaluate the proposed equivariant architecture against non-equivariant baselines on image restoration tasks and observe competitive performance with a significant increase in measured equivariance. Through extensive ablation studies, we also demonstrate that each change is crucial for its empirical equivariance. Our implementation is available at https://github.com/jscanvic/UNet-AF