Austrian Archaeological Institute – Austrian Academy of Sciences, Austria – Niki GAIL
Reflectance Transformation Imaging (RTI) is a computer aided method of photography to document objects in order to allow their following interactive analysis. Furthermore the subject’s surface shape as well as their colour attributes can be enhanced. The emerging, digital results reveal information of the surface which are not visible by the direct examination of the documented physical object.
RTI images result from a combination of a series of pictures taken of an object shot from a stationary camera position while light is projected from various positions. In that way images are produced showing different shadows as well as highlights. The visual information deriving from these pictures are the basis for generating a two-dimensional model of the surface which can be examined in an open source-software provided by Cultural Heritage Imaging (http://culturalheritageimaging.org/). The user is able to re-light the image virtually and analyse the surface. The images generated in such a way can be made open access and linked to other databases where information related to the documented objects already exists.
The method was already invented in 2001 and has since then many new tools, methods and uses have emerged. However, together with the HTL St. Pölten the Austrian Archaeological Institute / Unit Photography for the first time a system was developed, combining automatically the synchronized shooting of the camera with the various light projections of a hemispherical dome. Furthermore the construction material and the modular construction concept of the dome provides high mobility and allows an easy transport and use on excavation sites for the recording of specific finds.
As already mentioned, the RTI dome can be used for the documentation of various objects enabling specialists to analyse objects by visualizing its specific geometry, structure, and colour. In a test project the dome is used to digitize systematically the reproductions of inscriptions in the epigraphical archive of the Austrian Archaeological Institute which was founded at the end of the 19th century. This archive contains almost 6000 copies of paper and latex squeezes physically reproducing the surface of inscriptions on stone material. The collection contains epigraphic evidence of artefacts which have deteriorated or are lost. Sometimes an examination of these objects is nowadays not possible anymore. So, the digitization of these reproductions does not only serve the scientists’ need but also the issue of long term archiving and furthermore the preservation of cultural heritage. Up to now the digitization of these materials was just possible by a lot of work and just static images with a single light projection has been possible. Using RTI also made an improvement in efficiency of recording possible and breaks new ground in methods of documenting a specific group of archaeological objects and archive material. By comparing the squeezes and their different digital equivalents it can be shown in which way more information for the examination can be drawn from using RTI.