Small Finds Photography
Reflectance Transformation Imaging provides virtual access to an object so that it might be studied without interacting with the original find. This both minimises the risk of damage and provides access of material to remote researchers. Particularly useful in the area of small finds such as coins, jewellery and pottery sherds.
RTI photography uses a series of two-dimensional photographs to record a three-dimensional object and is particularly useful at recording surfaces with subtle low relief or very slight surface changes. This is done by keeping the camera in a fixed position while manipulating lighting conditions so shadows are cast across the object at varying but controlled angles.
At its most basic, RT Imaging operates under the principle that a surface illuminated from an acute angle will show a different luminance when lit from above. By taking multiple photographs under controlled lighting conditions, the RTI technique captures a precise record of an objects changing surface contours.
Reflective spheres are used to record the position of the light source. The light that is used to cast a shadow on the object also creates a specular highlight on the sphere. By finding this highlight in each photograph the RTI software calculates the lights position and then reproduces a model of what it would look like under these varying lighting conditions. In this way we can virtually move a light over the object as if we were holding it in our hand.
Importantly, RTI renderings have allowed archaeologists and other specialists to identify very degraded details on objects such as brick stamps and coins.
Reflectance Transformation Imaging (RTI) is a mechanism for manipulating multiple images under varying lighting angles to capture very subtle surface information.