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ELAD: Blind Face Restoration using Expectation-based Likelihood Approximation and Diffusion Prior
DescriptionBlind Face Restoration (BFR) aims to recover face images suffering from unknown degradations. A recent approach to solve BFR is via plug-and-play methods for image restoration, which combine a likelihood function with pre-trained diffusion models as priors. However, as the likelihood is inherently unknown in BFR, existing methods rely instead on heuristic constraints. This leads to suboptimal distortion and identity preservation metrics. We introduce Expectation-based Likelihood Approximation with Diffusion prior (ELAD), a novel plug-and-play approach that explicitly models the likelihood function for BFR. ELAD estimates the first and second moments of the likelihood distribution by employing a Degradation Estimator to predict the degradation sequence from the input. This enables principled Bayesian inference without requiring end-to-end training. Our method achieves state-of-the-art distortion and identity preservation results compared to existing plug-and-play BFR techniques, while maintaining competitive perceptual quality. As we show, while being plug-and-play, our method still rivals end-to-end trained BFR models.