Near-infrared modeling and enhanced visualization, as a novel approach for 3D decay mapping of stone sculptures

Representation of the surface pathology of heritage objects imposes a problematic task. It usually involves the implementation of on-site visual inspections, and diagnostic procedures on-site, and after sampling, through minimally destructive laboratory tests, to produce area-specific results or two-dimensional mapping visualizations. Mapping of stone weathering is usually performed manually with time-consuming two-dimensional approaches, thus losing the importance of topology and, in general, its three-dimensional metric quality. The recent introduction of modified cameras to heritage science has enabled enhanced observation at higher resolutions, concomitantly having the capacity to produce datasets that can be used for direct image-based three-dimensional reconstruction. With this article, we present a novel work combining near-infrared imaging using a modified sensor, and contemporary dense multiple-image reconstruction software, to produce spectral models of historical stone sculptures. This combined approach enables the simultaneous capturing of the shape of the historical stone surfaces and the different responses of deteriorated materials in the near-infrared spectrum. Thus, we investigate the capacity of the suggested method to assist three-dimensional diagnosis and mapping of stone weathering. We explore the usability of produced spectral textures via classification and three-dimensional segmentation techniques to obtain and assess different types of visualization. We additionally evaluate the produced models for their metric and radiometric properties, by comparing them with models produced with visible spectrum imagery, acquired with similar capturing parameters.