Diffusion-based restoration of corroded bronzeware images under a minimal-intervention framework: spatial-compliance indices and over-restoration risk diagnostics

Corroded bronzeware photographs preserve evidential textures such as corrosion and patina that should not be unnecessarily rewritten during digital restoration. This study evaluates LaMa, Stable Diffusion Inpainting, and ControlNet within a minimal-intervention framework. Synthetic-mask proxy tests were used to assess in-mask reconstruction, while real-damage cases were evaluated using spatial-compliance indices, risk maps, and blinded expert review. Diffusion models improved perceptual fidelity and global coherence in proxy tests, but in real-damage settings they produced greater boundary spillover and out-of-mask rewriting, indicating a higher risk of over-restoration. LaMa achieved comparable in-mask completion with markedly lower spillover. Experts regarded most outputs as draft-level aids rather than publishable conservation surrogates. The proposed framework supports transparent and auditable evaluation of restoration quality, intervention risk, and authenticity.