Lanpaint: Training-Free Diffusion Inpainting with Exact and Fast Conditional Inference

Abstract: Diffusion models generate high-quality images but often lack efficient and universally applicable inpainting capabilities, particularly in community-trained models. We introduce LanPaint, a training-free method tailored for widely adopted ODE-based samplers, which leverages Langevin dynamics to perform exact conditional inference, enabling precise and visually coherent inpainting. LanPaint addresses two key challenges in Langevin-based inpainting: (1) the risk of local likelihood maxima trapping and (2) slow convergence. By proposing a guided score function and a fast-converging Langevin framework, LanPaint achieves high-fidelity results in very few iterations. Experiments demonstrate that LanPaint outperforms existing training-free inpainting techniques, outperforming in challenging tasks such as outpainting with Stable Diffusion.