Background

Reflectance Transformation Imaging (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. It is a technique that uses a digital camera to take a series of photographs of an object with a different light position each time. A software package is then used to combine the information from the 40-120 images to produce a single three-dimensional rendering of the surface.

RTI also permits the mathematical enhancement of the subject’s surface shape and colour attributes. The enhancement functions of RTI reveal surface information that is not disclosed under direct empirical examination of the physical object.

RTI is frequently used in archaeology, palaeontology and forensics but could potentially be used in a diverse range of fields, from automotive manufacturing to medical diagnosis. Often the object to be imaged is very small - for example, a fingerprint. An RTI dome of 18 inches in diameter is capable of imaging artefacts up to a maximum dimension of 4.5”. Therefore, in cases such as this, a smaller dome of diameter less than 18” would be more advantageous, for portability and image quality.

Furthermore, it is often favourable to carry out the imaging process at the site of discovery. This would be the case for the example above, during fingerprint documentation at a crime scene. The fingerprint needs to be imaged before it can potentially be damaged during removal.

Technology Overview

Researchers at the University of Exeter have acquired Reflectance Transformation Imaging (RTI) equipment and are working in a multi-disciplinary team to expand the techniques’ capabilities.

The researchers at the University of Exeter are working to:

increase the clarity of RTI images and speed of acquisition
produce more mobile and cheaper systems

A smaller RTI system would make it possible to accurately execute image capture in the field. Attempts have been made to make the system smaller and some RTI capture has been tested using lighting rigs of various kinds, for example applications that use robotic arms and arcs. However, few have questioned the original design. The researchers are working on adapting the structure of the hemispherical dome in such a way that would make it collapsible, enhancing the dome’s portability and improving the utility of the technique in all areas of scientific and commercial interest.

Benefits

Carry out imaging at site of discovery
Capture surface shape and colour
Produce a 3D model of the target surface
Reveal additional surface information with mathematical enhancement

Applications

The researchers have a range of camera and domes for various purposes, these include:

archaeological finds including Roman graffiti
prehistoric axe heads
forensic residues
fungal growths

RTI has been comprehensively used in art, archaeology and even paleontology. However, potential research paths range from the detection of car windshield defects, to the early diagnosis of skin disease based on pigment contrast under specific light sources.

Further Details

There are two set ups for the equipment:

Highlight Based RTI which uses a fixed camera, handheld light source and target spheres in order to gather data on directionality of the images taken when reconstructing the 3D image. ()
Lighting Dome RTI which uses a fixed camera, and an LED light array inside a 1M dome in order to take a series of photographs of an object in a very controlled way. ()

Opportunity

The researchers would like to speak with potential commercial partners interested in imaging or the development of their RTI technology.

A Portable Reflectance Transformation Imaging System

Seeking