Reflectance Transformation Imaging (RTI) is a computation photography technique that captures the surface shape and color of the artefact and enables the interactive re-lighting of the subject from any light direction. Starting from a set of photographs acquired with a fixed camera under varying lighting conditions, RTI encodes the acquired data in a compact way, using view-dependent per-pixel reflectance functions, allowing the generation of new images using any light direction in the hemisphere around the camera place.

RTI tecniques has been employed in several projects for the virtual examination and study of the Cultural Heritage artefacts (high relief fossils, ancient stone tools, oil paintings, Cuneiform tablets, numismatic collection, the Antikythera mechanism). In this field the way in which the light interacts with the object is very important because the features of the material, reflectance behaviour, and texture can offer major perceptual and cognitive hints for the study of the artwork. In many cases the ability to interactively play with the light is more useful than the manipulation of an accurately sampled 3D shape, that is hardly able to capture all the interesting aspects of the artwork.

RTI technologies present several advantages:

  • inexpensive and widely available hardware (in many cases, just a digital camera and a light source)
  • scale well to both large and very small objects
  • a sampling density and a precision that most current 3D scanners are unable to reach, even under optimal acquisition conditions
For those reasons, RTI techniques are widely used in the Cultural Heritage field for documentation tools, giving a precious instrument to the specialists in the analysis and interpretation process.