Reflectance Transformation Imaging, or RTI as it is more commonly known, is described as ‘a computational photographic method that captures a subject’s surface shape and color and enables the interactive re-lighting of the subject from any direction. RTI also permits the mathematical enhancement of the subject’s surface shape and color attributes. The enhancement functions of RTI reveal surface information that is not disclosed under direct empirical examination of the physical object’ by Cultural Heritage Imaging https://culturalheritageimaging.org/Technologies/RTI/
I think of it as raking light on steroids- essentially you have a camera at the top which fires in sequence with individual lights located in a circle around the item, and then the registered images can be engaged with interactively through the freely available RTI Viewer https://culturalheritageimaging.org/What_We_Offer/Downloads/View/index.html