An important aspect in paper conservation is identification of the source of a paper used for a work of art. Identifying threedimensional characteristics such as laid lines, chain lines, and watermarks made in the manufacturing process of papers can aid in this process. Reflectance Transform Imaging (RTI) has become a point of interest, as it is particularly useful when the primary support is lined with secondary or even tertiary supports of canvas, boards, or other papers with different textures that would obstruct the use of transmitted light or X-ray imaging. Working with the surface normal and depth map generated from a 3D model based on the RTI data, we use frequency separation methods and Fast Fourier Transforms to isolate specific threedimensional features from the images.
Kurt Heumiller, Soyeon Choi, Jens Stenger, Chelsea Graham, "Post Processing of Reflectance Transform Imaging for Isolation of Surface Impressions" in Proc. IS&T Archiving 2016, 2016, https://doi.org/10.2352/issn.2168-3204.2016.1.0.15