Restoration of ancient Japanese manuscripts via the diffusion denoising restoration model and color space-based masking

Ancient Japanese manuscripts are invaluable cultural assets but are often degraded by stains, fading, and bleed-through. We propose a restoration framework integrating the Diffusion Denoising Restoration Model (DDRM) with a two-stage mask generation process combining Automatic Color Equalization (ACE) and Gaussian Mixture Model clustering across multiple color spaces. A key novelty is the use of binarized text masks as guidance signals for DDRM through noise masking, which constrains denoising to character shapes and suppresses background noise. A high-resolution patch-based strategy with feather blending further enables seamless reconstruction of both text and background. Experiments on synthetic degradations of The Pillow Book and real manuscripts such as Tsurezuregusa demonstrate significant improvements over binarization-based DDRM, with an average PSNR gain of 10 dB, SSIM increase of 0.17, and LPIPS reduction from 0.49 to 0.28. The framework enhances textual clarity, preserves red annotations, and offers a scalable solution for AI-driven cultural heritage preservation.