Adam Rabinowitz
This paper presents emerging computational techniques that allow the extraction of three-dimensional (or equivalent) information from standard digital photographs. It focuses on two techniques: photogrammetry and reflectance transformation imaging (RTI). Photogrammetry involves the extrapolation of 3D information from digital photographs taken of the same subject from different positions; RTI combines a series of photographs taken of the same subject from the same position, but with different lighting, to create still images that can be interactively re-lit. These techniques have demonstrated applications in archaeology, epigraphy, numismatics, and sigillography, as well as other areas of Classics research. They offer a much lower barrier to entry, in terms of both expertise and expense, than more familiar techniques such as laser scanning or 3D modeling. Much of the software involved is either open-source or relatively inexpensive and fairly easy to use; both software and photographic capture methods are simple and well-documented; and the datasets produced are easier to disseminate and archive than standard 3D models. Photogrammetry is now increasingly used to document and study the results of archaeological excavation (de Reu et al. 2013), while RTI is widely applied to objects for which surface relief is important (Earl et al. 2010, Earl et al. 2011).
Over the last two decades, laser scanners and computer-generated 3D models have received the most attention in the field of digital heritage documentation. Laser scanners are expensive, however, and the hardware, software, and technical expertise necessary to generate and manipulate 3D models are usually out of reach for small projects or individual researchers. There are also serious barriers to the documentation, long-term preservation, and dissemination of these models, which has implications for future research. A quieter revolution -- the near-total shift from film to digital photography -- is arguably more important for Classics. Digital cameras are inexpensive and are already in use in most Classics research projects involving visual information. Digital photographs are easy to archive, since well-established preservation standards already exist. At the same time, software that employs algorithms to extract additional information from digital images has grown much more powerful and easier to use. This paper discusses early practical experiments in the use of both these techniques at the site of Chersonesos in Ukraine from 2006-2008 (Rabinowitz et al. 2007; Rabinowitz et al. 2010), and then reviews the present state of the field, which has progressed rapidly since that time, with reference to several current research projects.