Title: Sketch Layer Separation in Multi-Spectral Historical Document Images,
Abstract: High-resolution imaging has delivered new prospects for detecting the
material composition and structure of cultural treasures. Despite the various
techniques for analysis, a significant diagnostic gap remained in the range of
available research capabilities for works on paper. Old master drawings were
mostly composed in a multi-step manner with various materials. This resulted in
the overlapping of different layers which made the subjacent strata difficult
to differentiate. The separation of stratified layers using imaging methods
could provide insights into the artistic work processes and help answer
questions about the object, its attribution, or in identifying forgeries. The
pattern recognition procedure was tested with mock replicas to achieve the
separation and the capability of displaying concealed red chalk under ink. In
contrast to RGB-sensor based imaging, the multi- or hyperspectral technology
allows accurate layer separation by recording the characteristic signatures of
the material's reflectance. The risk of damage to the artworks as a result of
the examination can be reduced by using combinations of defined spectra for
lightning and image capturing. By guaranteeing the maximum level of
readability, our results suggest that the technique can be applied to a broader
range of objects and assist in diagnostic research into cultural treasures in
the future.