M2Mamba: Multi-Scale in Multi-Scale Mamba for Blind Face Restoration

With the evolution of telemedicine, clean images, especially facial images, are crucial in areas such as symptom evaluation and cosmetic medicine. However, dealing with indiscernible facial images, a condition known as blind degradation, poses a formidable challenge for existing blind face restoration (BFR) techniques due to their inherently ill-posed nature. Thus, a delicate interaction between preserving local details and maintaining global geometries is desired. Despite advances in convolutional neural networks (CNNs), transformers, and denoising diffusion, where no matter serried convolutions, elaborately-designed self-attentions, or stochastic noises, tend to isolate either local or non-local features. To this end, a new candidate model termed Multi-Scale in Multi-Scale Mamba (M2Mamba) is proposed, which builds on a pioneering structured state space model-based network and includes three new components: multi-scale learned fusion module (MSLFM), multi-scale attention fusion module (MSAFM), and multi-scale inspired Mamba (MS-Mamba). Firstly, the MSLFM is adopted by extracting image-level global guidance from inputs of different scales, preserving intuitive perception yet enriching semantic understanding. Secondly, the MSAFM dynamically integrates features from various encoder stages. Thirdly, the MS-Mamba employs separate branches for both small- and large-scale receptive fields, benefiting modeling of long-range dependencies. In the final, M2Mamba is demonstrated on both synthetic and realistic benchmarks, showing comparable or better performance than state-of-the-art methods. The codes are available at: https://github.com/yanwd628/M2Mamba.