Reflectance Transformation Imaging (RTI) has been used for cultural heritage documentation since its introduction by Tom Malzbender in 2001. The technique allows for the recording of 3D surface reflectance properties and visualise them as 2D interactive images. The method can be used to investigate objects in various lighting conditions to enhance small surface changes, to bring out cracks, tool marks, scratches, pencil impressions and many more features that are not visible to the naked eye. The method is a valuable tool when examining coins, writing tablets and daguerreotypes, as features such as fine polishing lines, retouches and deteriorations can be identified. In this paper, an outline of the RTI technique will be given and a case study will be provided that encompasses a new processing algorithm for RTI that can extract greater levels of information than was previously available.
Hembo Pagi, James Miles, Andres Uueni, Stephen Hogarth, Kadi Sikka, "Reflectance Transformation Imaging in Daguerreotype Investigation" in Proc. IS&T Archiving 2017, 2017, pp 116 - 121, https://doi.org/10.2352/issn.2168-3204.2017.1.0.116