Reflectance Transformation Imaging

Archaeological Computing Research Group, University of Southampton

What is RTI?Reflectance Transformation Imaging (RTI) is an interactive photographic recording technique. Conventional photography consists of the production of an image depicting a scene lit in a particular way.

Reflectance Transformation Imaging allows the production of images within which the light can be moved and altered.

This virtual ‘relighting’ of a scene or object means that details which were not visible in a standard photograph can often be seen and allows information relating to the colour and reflectance of a surface to be more accurately assessed.

How does it work?RTI images are produced by taking multiple photographs of an object from a fixed camera position. Within each image the light source is moved to a different location around the object, effectively forming a dome of lights.

Using freely available RTI software these images are compiled into a single image file within which the user can interactively control the light source.

RTI data allow users to do much more than virtually move the light. The data can be used to virtually alter the reflective characteristics of an object, to add additional light sources to an image and to produce estimated 3D surface geometry. New tools for utilising RTI data are being made available all the time.

Can I make RTIs?The capture process is simple and involves only standard photographic equipment, all necessary software is

available freely online.

Find out more about RTI from the ACRG website: http://acrg.soton.ac.uk/

To download the software to make and/or view RTIs, visit the CHI website: http://culturalheritageimaging.org/

To see examples of how highlight RTI can be carried out using an iPhone and a desk lamp, visit the website for the community archaeology project Re-Reading the British Memorial, which is training special interest groups to use RTI to record headstones and memorials: http://ourti.org/

Figure 1: RTI of St. Peter inscription, a reused stone now part of the porch entrance of

Holcombe Church.

Figure 2: RTI of a headstone at St. George's Church, Portland. An RTI

can also be used to mathematically enhance the object’s colour and surface attributes, as

shown by the image on the right.