Reflectance Transformation Imaging and Churchyard Surveying
RTI is a 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 was first described by 2 research scientists working at Hewlett-Packard Labs in 2001 and was referred to as Polynomial Texture Mapping. Their original work was then further developed by an international team applying it heritage recording
In essence RTI, as applied in the field to large fixed objects, consists of taking multiple photographs from a fixed position, moving the light source between each exposure and processing the resulting images. The resulting file can effectively have the lighting ‘replayed’ with the appropriate software. The approach can also be used in the laboratory for recording small artifacts, in this case a series of LEDs mounted in a sphere are triggered in sequence to produce the lighting pattern.