Reflectance Transformation Imaging
The project utilized advanced digital imaging technologies to support the best visualization possible of medieval coins. The primary application used was Reflectance Transformation Imaging (RTI) which in conjunction with Superzoom imaging capacity can provide exceptional clarity, texture details and the ability to manipulate the lighting source on the surface of coins. As a result, each coin of the collection can be visually explored within a dedicated 'window' featuring an array of helpful tools and instructions. The overall imaging effort was developed and materialized by the The Cyprus Institute's Imaging Cluster for Archaeology and Cultural Heritage (ICACH)
What is Reflectance Transformation Imaging?
RTI is a computational photography method. It relies on extracting reflection information from several photographs captured from a fixed point under a “known” hemispherical coordinate lighting environment. An algorithm re-synthesizes that information into a new photorealistic representation that has dynamic light properties based on empirical mathematical illumination models engender from the fields of computer graphics, computer vision and optics. The final RTI image examined on a screen is not a three-dimensional model but rather a two-dimensional image that looks-alike a 3D representation with important advantages over it in terms of texture accuracy. Among other uses such as in medicine and forensics, the application of RTI in archaeology has proved to be particularly effective. An indicative example was the application of RTI technology in the successful decoding of the Antikythera Mechanism inscriptions on the metal fragments of the famous ancient device.
RTI was originally invented by Tom Malzbender and Dan Gelb at Hewlet-Packard Labs. Their 2001 publication presented their research results, methodology and tools described as Polynomial Texture Mapping (PTM), a term still used as an alternative to RTI to describe the algorithm used in the imaging process. Further developed and enhanced by the West Semitic Project at the University of Southern California (USC) and Cultural Heritage Imaging (CHI), RTI offers remarkable possibilities in mapping the relief qualities of objects’ surfaces. Inscriptions, incisions, decorative relief designs and even painting brushstrokes on an array of archaeological material and surfaces such as stone, clay, marble, coins, paintings, mosaics, sculpture, jewellery and other minor objects, can be documented with accuracy.