Two Saturdays ago a workshop on advanced imaging techniques was held at the Egypt Exploration Society in London. It was taught by Dr Kathryn Piquette, of the UCL Centre for Digital Humanities. The purpose of the workshop was to train those working in the field in Egypt in a new generation of imaging techniques which are both suitable for site work (not requiring laboratory type working conditions and involving relatively little equipment) and affordable – therefore available for those working without access to large budgets – ideal for an independent conservator in the field such as myself, as well as for many other colleagues and professionals.
The workshop covered an overview of digital photography for heritage documentation, looking at goals and deliverables within the constraints of time, space, finances and technical capabilities. This overview included a section on photo stitching and the related available software; the ability to stitch multiple photos being invaluable when trying to record and document larger surface areas – such as wall painting, carved relief or architecture – while at the same time achieving a high level of detail in the resulting document.
Kathryn went on to detail two specific imaging techniques. The first of these was Dstretch (available on request at http://www.dstretch.com/ with a donation), a free plugin for the public domain, open source, image processing software ImageJ. Dstretch, developed to examine rock art, works by enhancing the colour separation of an image – which has the result of bringing out underdrawings, original corrections and details – or colour invisible to the naked eye. Dstretch does not require any specific lighting or special filters – making it an ideal tool for fieldwork.
I had already been aware of Dstretch, working in Egypt at the beginning of the year, and seen some exciting findings from it as applied to the study of wall paintings, and had started to practice with the App version for mobile phone. This was a good starting tool, and would also be useful to make the first assessment of an area, or to help select areas of interest for later photography and examination with the full programme via laptop.
We had a practical session using the Dstretch programme on images provided by Kathryn, of an area of Coptic graffiti and a stela, with dramatic results. I have subsequently experimented using an earlier photo of the cat from the tomb of Sennefer (the Belgian Archaeological Mission in the Theban Necropolis of the Université libre de Bruxelles and the University of Liège project) (see below), the Dstretch images bring out a lot more detail of the cat’s marking and the brushwork, as well as the underdrawing and changes of position.
While Dstretch is ideal for enhancing faded colour and aiding understanding and reading of an area, it also makes an interesting tool for the examination of a damaged surface, or one obscured by a dirt layer. Below are the Dstretch images created when I applied it an old conservation process photo from the MANT project (image courtesy of MANT), of a half and half cleaned area of frieze from the tomb of Sennefer. Such a tool appears to be interesting both to inform conservation decisions and cleaning strategies, or could be used to allow the reading of areas too vulnerable, or with too insoluble a dirt layer, to allow safe cleaning.
The second imaging technique the workshop covered was reflectance transformation imaging (RTI) – a high resolution, non-invasive and non-destructive imaging technique, used to document fine surface details – shape, texture and colour, in particular. RTI images are created from information derived from multiple digital photographs of an object shot from a fixed camera position, with lighting projected from a different angle in each photo in a systematic way – producing a series of images of the same subject with varying highlights and shadows. The images are then processed together to produce a single image that can be relit interactively and the photographed surface examined in extraordinary detail in different viewing modes via a computer screen.
This examination reveals surface information not evident via direct surface interrogation. The purposes for conservation would include examination of previous interventions, damage, condition and information as to original construction techniques – all of which guide the selection of an appropriate conservation approach.
The workshop covered a hands-on practice in the setup and capture of photos for RTI using demonstration objects (pictured above), this was followed by image processing and examination of RTI images in a range of viewing modes using provided data sets. This training was based on that provided by domain experts Cultural Heritage Imaging (CHI) who provide RTI software (both an image viewer and builder) and user guides freely for download at http://culturalheritageimaging.org/Technologies/RTI/. CHI also offer a reasonably priced complete RTI ‘highlight capture starter kit’.
The whole workshop was eye-opening, both in term of what can be achieved using these affordable techniques, and in what is available as open sourced donationware or freeware. I particularly like the ethos of these methods – produced to be practical for on-site conditions and for those on limited budgets, and not purely for the preserve of large, and generously funded, institutions.
Kathryn is offering a four-day RTI training course at UCL in September http://ucl.ac.uk/lifelearning/courses/reflectance-transformation-imaging-training which I would have loved to have attended but unfortunately will be working on site on a conservation project over those dates.