Reflectance Transformation Imaging (RTI) is computational photographic method that captures a subject’s surface, shape, and colour, and enables the interactive re-lighting of the subject from any direction. 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.

Each RTI resembles a single, two-dimensional (2D) photographic image. Unlike a typical photograph, reflectance information is derived from the three-dimensional (3D) shape of the image subject and encoded in the image per pixel, so that the synthesized RTI image “knows” how light will reflect off the subject. When the RTI is opened in RTI viewing software, each constituent pixel is able to reflect the software’s interactive “virtual” light from any position selected by the user. This changing interplay of light and shadow in the image discloses fine details of the subject’s 3D surface form.

At the Ure we learnt about the technical process of RTI thanks to a professional photographer who offered a tutorial based on the information found in culturalheritageimaging.org However, we came up with our own handbook based on our own the learning experience: museum staff, volunteers, and Erasmus interns all partook in this project. Please, see the link below.

RTI works better on flat surfaces, so we decided to start with two objects. First, we took pictures of these artefacts with a moving light-source following a “dome” or “umbrella” pattern; then, we transferred them into RTI generator to create a series of “finished files” that were processed to be analysed in the RTI viewer. We were able to spot tool marks and tiny details that were only visible using this method.