Cross-Spectral Feature Fusion for Multispectral Document Binarization

Overview & Synopsis

Historical document binarization remains challenging when faded ink, bleed-through, and background degradation exhibit wavelength-dependent behavior across visible and near-infrared observations. This study investigates whether adaptive cross-spectral feature fusion and targeted structural guidance can improve multispectral document binarization beyond fixed fusion and generic attention mechanisms. Four registered SMADI bands at 500, 600, 700, and 1000 nm are processed using a multi-branch conditional generative adversarial network (cGAN). Visible, NIR, and structural feature streams are fused at encoder depth L = 3 using spatial- and channel-wise softmax gating, while auxiliary edge maps derived from selected VIS-NIR band pairs provide targeted structural guidance. Nine controlled fusion and structural configurations are evaluated using five-fold document-level cross-validation, DIBCO-standard metrics, and Holm-corrected statistical testing. The F3 + NIR edge-guided configuration provides the strongest overall performance among the evaluated models, achieving mean F1 = 0.7916, p-FM = 0.8044, and IoU = 0.6654. Relative to the fixed Mid AVG baseline, it improves F1 by 0.0269, p-FM by 0.0360, and IoU by 0.0321, with all three gains remaining statistically significant after Holm correction. Mean NRM and DRD are also reduced, although these reductions are not statistically significant after correction. Targeted cross-spectral structural guidance provides an effective mechanism for regulating intermediate multispectral fusion, improving primary foreground-overlap performance while retaining the complete four-band observation.