Tuesday, 13 March 2012

Reflectance Transformation Imaging (RTI): A taster

In my previous post I referred to the way in which the digital imaging technique Reflectance Transformation Imaging (RTI) can make visible surface marks which may not be apparent with the naked eye -- or at least enhance features that are difficult to see depending on lighting conditions and how you look at an object (more on seeing/looking in another post, but just to highlight here that this is not necessarily a neutral activity!).

I am exploring the possibilities of inserting an RTI viewer into this blog, or otherwise linking to one in order to show examples of my RTI results. In the meanwhile, if any reader comes across a solution -- please do let me know. For those unfamiliar with the kinds of results one can achieve with RTI, here is one of my favourite examples from the AHRC-funded University of Oxford and University of Southampton RTISAD project I worked on in 2010-2011 (for more information check out our interim report).

Here is a detail of a stunning portrait from the mummy of a Roman woman who lived around c.160-170AD. She may have been buried at El Rubaiyat in Egypt where the portrait is thought to have been found (and now housed in the British Museum). Her portrait is made with encaustic on limewood and added gilding. The top image is an RTI output with even 'default' lighting; the middle image shows the 'diffuse gain' rendering mode which enhances the perception of surface shape features for interpretive purposes; and the lower image exemplifies the 'specular enhancement' mode which renders the shape-based reflections to also enhances the perception of the surface shape.

(EA 65346. All © Trustees of the British Museum)

I hope this example gives some idea of what RTI can do to aid research of material surfaces. The aspect of RTI that I cannot show here on the blog (yet...) is the ability to reposition the light virtually. This re-lighting feature together with the different rendering modes constitute a powerful toolkit for studying the details of material surfaces, whether one is a conservator, art historian, text scholar, archaeologist or even...undertaking criminal forensic investigation!!

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