Revealing hidden images with Crediton Parish Church
Reflectance Transformation Imaging is a computational photographic method that captures a subject’s shape and colour and enables the interactive relighting of the object from novel directions.
This techniques enables researchers reveal ancient imagery that is no longer visible to the eye. It allows mathematical enhancement of the subject’s surface shape and colour to reveal surface attributes that are not easily visible under direct examination of the object.
Dr Jacqueline Christmas, director of the University of Exeter’s RTI group, was part of a project with Crediton Parish Church to reveal imagery using RTI. The carvings which were the focus of this particular project were located on the Sedilia (a set of (usually) three seats, located on the South wall of a church, for used during mass by the priest and his assistants).
The Sedilia had been damaged during the Reformation (between 1547 and 1553), such that the images were largely no longer visible to the eye. The team used RTI to analyse these damaged areas of the church and reveal aspects of artwork which had been previously lost. These artworks, which the team were able to visualise, provided important historical and cultural insight into the church.
Separately RTI was also used to reveal text carved into headstones in the church graveyard. The team were again able to reveal previously lost information contained on headstones which had all been damaged or extensively weathered over time. This has allowed the church to maintain accurate archives.
RTI images are created from information derived from multiple digital photographs of a subject shot from a stationary camera position. In each photograph, light is projected from a different known, or knowable, direction. This process produces a series of images of the same subject with varying highlights and shadows. Lighting information from the images is mathematically synthesized to generate a mathematical model of the surface, enabling a user to re-light the RTI image interactively and examine its surface on a screen .
 Taken from “http://culturalheritageimaging.org/Technologies/RTI/” on 21/08/19