The Preliminary Attempts to Quantify the Three-dimensional Details of Document Surfaces with Reflectance Transformation Imaging

Reflectance Transformation Imaging (RTI) is a computational photographic method that captures a subject’s surface shape details and enables the interactive re-lighting of the subject from any light direction. Multiple rendering modes of this computational photographic method could be very helpful for the analysis of morphological characteristics, among which the normal visualization mode provides the three-dimensional details of the surfaces of documents. However, since there might be visual illusions among different examiners, analyzing three-dimensional details just by observing the normal maps seems incomplete. With the method developed by the authors, the pen pressures of signature samples were experimented on by quantifying the three-dimensional surfaces with the normal data derived from the normal maps. By comparison, the 3D data derived from the normal maps of the signatures were similar to those generated with Confocal Laser Scanning Microscopy. Normal errors were discussed via the quantification method as well. For the inherent error of the RTI technique, the methods of error correction were developed by the authors.