Ultraviolet RTI

A painted and incised ceramic vessel was used as case study in an attempt to evaluate the efficiency of Reflected UV (UVR) RTI and UV induced visible fluorescence (UVF) RTI. The Highlight RTI data capture took place at the archaeological imaging laboratory of the University of Southampton, using a UV-VIS-IR modified DSLR camera, adequate filters […]

A painted and incised ceramic vessel was used as case study in an attempt to evaluate the efficiency of Reflected UV (UVR) RTI and UV induced visible fluorescence (UVF) RTI.

Gnathian skyphos from the University of Southampton Archaeological Collection

Gnathian skyphos from the University of Southampton Archaeological Collection

The Highlight RTI data capture took place at the archaeological imaging laboratory of the University of Southampton, using a UV-VIS-IR modified DSLR camera, adequate filters and lighting. The reflected UV-RTI datasets were captured with a UV transmitter and an IR barrier filter. The UV induced visible fluorescence RTI datasets were captured with an IR and an UV barrier filter.

The UV induced visible fluorescence image reveals the remains of conservation materials on the surface of the ceramic skyphos and the previous repairs, because of the visible fluorescence emission of common adhesives used. The UV induced visible fluorescence RTI enables the user to virtually move the radiation source around the object leading to numerous different visualizations. In that way the conservator can reach a better understanding about the morphology of the previous repairs.

Reflected UV-RTI offers the opportunity for enhanced examination of subtle surface variations; the remains of the conservation materials, the differentiations of the glaze due to its poor preservation and the salts’ efflorescence. The technique provided in a single file a combination of axial and UV imaging. It is notable that the axial positioning of radiation sources in reflected UV imaging is advantageous and is proposed for recording of scratches and smudges.

 

Gnathian skyphos, back side. RTI visualizations in default rendering mode, comparison of visible, infrared at 950nm, UV reflected and UV fluorescence (from left to right)

Gnathian skyphos, back side. RTI visualizations in default rendering mode, comparison of visible, infrared at 950nm, UV reflected and UV fluorescence (from left to right)

Gnathian skyphos, back side. Normal maps, comparison of visible, infrared at 950nm, UV fluorescence and reflected UV (from left to right).

Gnathian skyphos, back side. Normal maps, comparison of visible, infrared at 950nm, UV fluorescence and reflected UV (from left to right)

The synergy of RTI and UV imaging, results in an enhanced methodology for non-destructive examination and leads to different views of artefacts, which can be used for documentation, presentation, communication and research purposes.

UV-RTI visualization:

  • Emphasizes subtle variations in the outer layer that are not clear in the visible spectral area
  • Reveals episodes of the museum life of the artefact
  • Reveals manufacture evidence and decay relevant to varnish layer or glazes

 

Student Research: Recording Church Graffiti

Vicky Man is currently an undergraduate Archaeology student. She dug at Basing House in 2013, and is now coming into her third year at the University of Southampton. Vicky has been working on her major project since the beginning of the summer and spent the field season this year with us at Basing House collecting […]

Vicky Man is currently an undergraduate Archaeology student. She dug at Basing House in 2013, and is now coming into her third year at the University of Southampton. Vicky has been working on her major project since the beginning of the summer and spent the field season this year with us at Basing House collecting data for her research and working with staff and volunteers to think about how to tackle her fascinating topic.

Vicky has written a blog post introducing her research. The Basing House team have been recording small finds from the 2014 season using the technique that Vicky outlines below. Last year, in fact we used RTI to help with the interpretation of the Roman coins that we found (see this great blog post by Phoebe).  This year, we are using the technique to record a selection of objects, and we are hoping the technique will answer specific questions. Look out for future blog posts on these findings.

We will also write a blog post soon describing this technique to you. Because RTI uses open source software it is a low cost option for recording similar artefacts, with the only expense being a digital SLR camera. In the meantime, you can check the Re-Reading the British Memorial Project. This is a project directed by Gareth and me; we train special interest community groups to use RTI to record church memorials and so much of the guidance for the technique is available through the project website.

We can’t wait to see some of the results. Rest assured, we will be asking Vicky to write a follow-up blog post on her findings later in the year!

Thank-you to Vicky for this excellent blog post!

Recording Church Graffiti

by Vicky Man

Introduction

It was always going to be a daunting process, finding a suitable dissertation topic for my third and final undergraduate year. The fact that my time at university had flown past was astonishing enough, let alone the fact that I had to find something of interest to do a dissertation on! It was lucky then, a couple of things caught my attention, during my time at Basing House 2013.

First, it was an introduction to RTI (which will be talked about more), a digital form of recording used in archaeology, that I didn’t even know existed prior to this dig! Second, it was a visit to St Mary’s Church (incidentally down the road from the Basing House site) on a rainy day.

I knew I wanted to use RTI, so it naturally led me to use St Mary’s Church as a case study. But what would I be recording? After a couple of visits to the church, it was apparent that graffiti was scattered all over the church interior. Therefore, I decided to investigate the use of RTI on church graffiti present there.

What is RTI? And graffiti…?

RTI stands for ‘Reflectance Transformation Imaging’, a computational photographic technique that records the surface, holds the potential to uncover details that is hard to see by the naked eye. In order to form the final RTI image, a series of images are used. The photos are taken from a fixed point. What differs in each photo is where the light source is directed from; in this case, a camera flash is used. This form of RTI is called Highlight RTI. The flash is systematically moved around the object to form an imaginary ‘dome’ shape. As a result, each photo will vary in highlights and shadows that will show in the final photo.

Graffiti is often described negatively nowadays; however, what sets graffiti found today apart from graffiti found in the past, is not only the artistic style, but also the meaning behind them. There is of course similarity perhaps in the human need to be remembered, therefore we inscribe ourselves in pieces such as literature in hope that we will be remember once we are long gone. However, what makes graffiti interesting in a church setting is because of the time and effort it must have taken to inscribe onto the hard walls.

The set-up for a Highlight RTI. Vicky is holding the lightsource, which is triggered remotely in time with the camera. The reflective sphere captures each light highlight so that the software can patch together all of the photographs in an interactive file.

Example Graffiti

A tiny snapshot of some of the graffiti from St. Mary’s Church.

The Process!

Before getting to the actual recording, I practiced the technique by recording a few artefacts (thanks to the lovely Jude for providing a few artefacts to record!). There were a few technical hitches, getting used to the equipment, but I got there in the end, successfully recording all the material I needed for my dissertation.

Nicole and Vicky recording in St. Mary’s Church. Photo by Juliette Bijoux.

Vicky working on recording some of the harder to get to graffiti in St. Mary’s Church.

Final words…

How can we tell it is even graffiti and not damage? When was it made? What is the meaning behind this symbol? These are just the few questions that arise. RTI is a great technique to use as part of my investigation into graffiti at the church. Now what’s left is answering why.

A massive thank-you to Nicole, Gareth, Yvonne, Jude, Chris, Peter, Phoebe and Rev. Alec Battey for kindly supporting me in my dissertation work.

 Vicky Man

 


Filed under: 2014 Excavation, Conservation, Data Processing, Finds, History, Images, Student Reporter, Student Research Post, Vicky Man Tagged: aerial photographs, apotropaic, artefacts, camera, church, computational photography, esoteric, graffiti, image, interpretation, marks, memorials, Old Basing, OuRTI, petroglyphs, re-reading the british memorial, reading, recording, reflectance transformation imaging, rti, st. mary's church, symbol, walls

Postcards from the field: Studying the Neolithic figurines from Koutroulou Magoula, Greece

Clay Neolithic figurines are some of the most enigmatic archaeological objects, which depict in a miniature form humans, animals, other anthropomorphic or zoomorphic beings, and often hybrid or indeterminate entities. Figurines have excited scholarly and public imagination, and have given rise to diverse interpretations. The assemblage from Koutroulou Magoula, a Middle Neolithic site – 5800-5300 […]

Clay Neolithic figurines are some of the most enigmatic archaeological objects, which depict in a miniature form humans, animals, other anthropomorphic or zoomorphic beings, and often hybrid or indeterminate entities. Figurines have excited scholarly and public imagination, and have given rise to diverse interpretations. The assemblage from Koutroulou Magoula, a Middle Neolithic site – 5800-5300 BC – in central Greece (excavated under the co-direction of Prof. Yannis Hamilakis – University of Southampton/British School at Athens and Dr Kyparissi-Apostolika – Greek Ministry of Culture), offers a unique opportunity to revolutionise the way we study and understand prehistoric figurines.

The video presents the project ‘Corporeal engagements with clay’ (funded by the British Academy/ directed by Prof. Y. Hamilakis) showing aspects of our work in recording, visualising and replicating the figurines from Koutroulou Magoula by using a tailor-made database, as well as drawing, photography, photogrammetry, laser scanning, reflectance transformation imaging and 3D printing.

 

True Gigapixel RTI

The ACRG has always been an integral part within the recent development of RTI. ACRG’s involvement began with the AHRC funded RTISAD project where we piloted the technique on inscribed ancient documents and archaeological artefacts. We likewise raised awareness of RTI in research and public communities in the UK. This has since led on to several organised community […]

The ACRG has always been an integral part within the recent development of RTI. ACRG’s involvement began with the AHRC funded RTISAD project where we piloted the technique on inscribed ancient documents and archaeological artefacts. We likewise raised awareness of RTI in research and public communities in the UK. This has since led on to several organised community days such as the one held at Winchester Cathedral and the Re-reading the British Memorial community driven project that focuses on churches. The project has completed a number of these community days and is led by ACRG members Gareth Beale and Nicole Beale.

Since the RTISAD project our understanding of the technique has greatly changed. As new technology becomes available we are adapting our methodology to create new research avenues that not only help our department stand out but it also helps the wider community. Examples of this can be seen in the work completed by Eleni Kotoula who has created different methodological approaches in Microscopic RTI, Multispectral RTI and Transmitted RTI. Eleni, having come from a conservation background, saw potential in the technology within her own studies and many other members of ACRG are now utilising these methods as general practice within their own investigations. Further developments can be seen in the work completed by David Selmo who created the first underwater RTI dataset. He saw the potential that it had within maritime studies, developed the technique and then tested the methodology in open waters.

RTI has become an important tool within archaeological studies and at the ACRG we are always trying to develop this further. We have a number of examples and blog posts regarding this. My main personal issue however is that although our research has developed to introduce new varieties of RTI recording, our limitation has and will always be the resolution of the camera used. When RTI was first introduced by Tom Malzbender through his PTM viewer, the issue of resolution was not considered as the technology focussed on the changing surface detail and required no further detail. This has dramatically changed with the introduction of the technology within cultural heritage. Resolution is everything when considering images; the high the resolution the better, as minute details may make all the difference in fully understanding an artefact. This is especially true when studying pigment analysis. Eleni has considered this within her work by using microscopic RTI. This analysis however only works when you have small fragments where you know that the object recorded has potential in revealing information. What if I wanted to record a still standing Roman marble inscription that was once painted? I would only be able to record this by using the highlight method and as I have tried to explain, I would be limited by the resolution of the camera available.

The PTM fitter designed by Hewlett-Packard only has the capability to process a dataset that contains a height of around 4000px. This means that recent cameras that have been developed, such as a Nikon D800e (36mpx camera), cannot be used as the pixel height of a full image is 4912px. I have tried many times to process this dataset on different computers using the original ptm fitter and was left with the same memory error code. We purchased a Nikon D800e to enable us to further develop the technology and to allow us to examine the artefacts that we record in greater detail. As the PTM fitter could only process a limited number of pixels we were left having to reduce the resolution of the images in order to process them, which goes against the original idea behind its use. This however changed when I was introduced to a new ptm fitter developed by our ECS department, in collaboration with John Cupitt, which utilises an imaging program named VIPS. This PTM fitter runs via a command line but it enables users to process images that exceed the 4000px height. As a result of this we are now able to process the 36mpx images produced from the D800e and gain a higher resolution RTI dataset.

Having the ability to produce RTI datasets that contain higher resolution images, I began to consider the potential that this has within archaeology and my thoughts went back to the Gigapan RTI dataset that myself and Hembo Pagi captured in 2011 at Portus. The department had just bought a Gigapan Epic Pro and we were eager to try it out on site. Part of the work that we completed at Portus was the recording of panoramas and we had some success in producing high resolution images that far exceeded the capabilities of a normal camera. The system works by choosing a starting and finishing point, defining the available field of view, from which a series of automatic overlapping images are captured and then stitched together to produce a complete image. The camera that we used on site at Portus was a Nikon D3X (24mpx). As we were able to focus the individual images on small sections, it meant that the 100 or so images captured each contained 24mpx. When combined it meant that the overall image was highly detailed. As we had the equipment with us we decided to capture a RTI dataset using the same methodology used in the panoramic views. Portus has an abundant number of brick stamps and we carefully chose one that would enable us to capture the necessary dataset. We placed the Gigapan in front of the brick stamp, at a far enough distance away where lens distortion would not affect the stitching results. We took ten individual captures following the same methodology as used in a normal highlight capture. The Gigapan took a series of images where the light source was fixed. The camera had to move in order to capture the small detail but the Gigapan provides a memory function. After the Gigapan captured the automatic images we then moved the light source and simply replayed the last action of the Gigapan, making sure that we did not move the equipment in anyway. An example of the final rendered image can be seen below.

High resolution RTI dataset of a Portus Brick stamp

Although we captured this data in 2011 we were unable to process the ten test images until the VIPS PTM fitter was given to us, as we still had the same issue with processing images with a height of over 4000px. In order to produce these images, the Gigapan images had to be processed in a specific way. Kolor Autopano Giga was used to stitch the separate images but rather than batch process the Gigapan images automatically, I processed one and saved the control points. As different lighting positions were used it meant that certain RGB values would differ in each image and it could have affected the positioning of the images (if processed automatically) which in turn would affect the RTI dataset. Having a saved version of the control points that the software uses to stitch the dataset together meant that each separate light position image would be processed in exactly the same way and follows standard procedure within any RTI documentation.

Having now completed a test with these ten images my attention turned to completing a full RTI capture. I successfully managed to complete this several  months ago using the same set up as we had at Portus. The below image shows the data capture in process with the Gigapan, object and shiny ball all being in a fixed position with only the light source truly moving.

GigaRTI setup using a Gigpan and mounted flash

Gigapan RTI set up for a 18th Century brick stamp

The item recorded within this follow up test capture was a brick stamp from the 18th century. The brick stamp belongs to Penny Copeland and was chosen because it has a great level of detail engraved into at the time of its firing. The brick I confess was recorded upside down but the intention of this data capture was to test if the VIPS PTM fitter could process a large number of images. The object was recorded using our Nikon D800e camera (36px) and a 200mm lens. The data capture took place in our dedicated imaging lab allowing us to have the camera set up far enough away from the object to avoid lens distortion problems. In total 42 seperate RTI images were captured and then processed. As I had used an even higher resolution camera and a lens that focused on very small detail, I was able to produce two separate rendered images using the same methodology discussed earlier. I was therefore able to produce images that could be used in a RTI dataset at resolutions of one gigapixel (one billion pixels) and two gigapixel (two billion pixels) and examples of these datasets can be seen below. These were then processed via the Cultural Heritage Imaging RTI builder in order to generate lp files and then run directly within the VIPS PTM fitter. This took some time to process because of the file size but we were able to produce PTM files of both. Having produced the datasets we encountered another problem in that we could not open the files as the standard RTI viewer runs out of virtual memory. The one gigapixel RTI file size is 8.52gb! Although this is problematic, I am currently working with the University’s supercomputer department, Iridis, in order to create a GUI that will enable us to open the dataset and the ACRG are currently working on developing a new web based RTI viewer that will enable online sharing of these datasets. Once this has been completed I will add a follow up blog post showing the RTI rendered images.

 

 

One gigapixel RTI dataset. To view in full screen please visit the iip server where it is hosted

Two gigapixel RTI dataset.

In the mean time discovering that we are now able to process large datasets means that we can rethink our approach to how we use RTI within Cultural Heritage. The image resolution is always hard to calculate and this is especially true when considering the dataset that we have. Normally the number of lines per inch a camera can resolve at the sensor equates to the resolution of the image produced. Within our own data we are not using a single sensor but rather a sensory array so any calculation of resolution must be based as an expression of pixels at a particular point of the image. In the two gigapixel dataset we are able to calculate, using the scale provided within the image, that 1cm in the real world is represented by (is sampled into) 890 pixels. Therefore each pixel is 1/890 cm = 0.001123cm, Meaning that a pixel equates to 11 microns resolution. This resolution, if correct, means that we were able to capture and process a RTI dataset at a microscopic resolution without the need of a microscope and highlights the potential that this has within specific artefact studies. Of course this technique will not replace microscopic analysis but rather allow users to view larger areas using the same RTI analysis as usual, but then allow them to also have the microscopic detail if required.

The basic technique of this high resolution RTI data capture is still under development and much of the software is still being updated to incorporate the need for higher resolution images. At the ACRG we have taken this one stage further by producing a true gigapixel RTI dataset. This is of course an extreme and for most studies is not needed. However the technology and methodology now exists that will enable future researches to use this technique in whatever way they feel and with whatever image size they capture their data with. For those debating whether or not this next step in RTI is worthwhile, I will go back to my earlier question regarding the standing Roman marble inscription. What method should I use? Normal highlight RTI, Microscopic RTI or Gigapixel RTI? I will let you decide!

 

Update on the Hoa Hakananai’a Statue

In 2012 ACRG members, James Miles and Hembo Pagi, completed a series of RTI captures and a photogrammetry model of the Easter Island Statue, Hoa Hakananai’a, which is currently housed in the British Museum. Since then, in collaboration with Mike Pitts, we have examined the results of these RTI files and compared them with the photogrammetry […]

In 2012 ACRG members, James Miles and Hembo Pagi, completed a series of RTI captures and a photogrammetry model of the Easter Island Statue, Hoa Hakananai’a, which is currently housed in the British Museum. Since then, in collaboration with Mike Pitts, we have examined the results of these RTI files and compared them with the photogrammetry model. A brief discussion of this work can be seen in a previous blog post. The methodology that we utilised allowed for a full analysis of the statue that has previously been impossible. It allowed us to examine the RTI files in fine detail through the changing surface detail identified through the raking light and rendering modes. Where we thought we had identified something important we could then see if it existed in the 3D model. This comparison then allowed for a combination of the subtle 2D differences in the RTI to be mapped and compared to the 3D surface differences in the virtual replica of the model. Through this we were able to clear up some of the often ambiguous interpretations of the petroglyphs. More on our results and methodological approach can be seen in our recently published Antiquity paper, our Antiquaries Journal paper, Mike’s paper in the Rapa Nui Journal and our soon to be published paper in the Proceedings of the 41st Computer Applications and Quantitative Methods in Archaeology Conference. The work has also gained a lot of public interest and our research features in recent online publications which are a Google search away.

Since these publications I have been working on ways, as part of our initial research aims, at producing online versions of the datasets, where users can view and manipulate the records that we have. This will allow different people, with different backgrounds to come to their own conclusions. Part of this blog post is to make available for the first time, the RTI files that were produced within our investigations. At Southampton we are working on creating a newer and better online RTI viewer, but at the minute we are left with having to produce low resolution datasets for online use. The following then is a severely reduced RTI dataset but the results are still evident none the less. The RTI files have been separated into five different sections, one of the front and four of the back (with a slight overlap) to allow for a greater understanding.

In Van Tilburg’s recent response to Mike’s paper (in the same Rapa Nui Journal), she states that “The major issue with regard to PTM (RTI), is that to advance a thesis of interpretation and avoid bias one must allow review of all of the images produced, not just selected ones that support a given point of view.” I would just like to clarify this statement as it seems that the purpose of RTI has been overlooked. Each of the five files contained between 57–87 images as gathering anymore than 90 would be counter-intuitive through the way in which the individual images are processed. With Van Tilburg’s understanding it is clear to see that there has been some confusion as to how an RTI is produced. Rather than examine each individual image, the RTI builder combines all of the static images and merges them together into a file format that allows for the virtual movement of a light source. This then moves away from the need to examine each image, which I agree, could provide incorrect conclusions. Instead it allows for a greater understanding and greater depth of investigation through the combination of these different static images and movement of virtual light, as it removes the ambiguous and problematic context of previous investigations of the statue. Van Tilburg also negates to mention the use of our virtual model (which was based on 150 images) within our interpretations as she wrote her article before ours were fully published. Going from the RTI files to the 3D model is something that has never been done before in reference to this statue and her argument of using selected views is wrong and short-sighted. She has made derogatory remarks regarding our work without viewing the entirety of our research. This is something that needs to be corrected and so also included within this blog post are updated versions of our photogrammetry model through different online viewers. This will then allow you to make a fuller and more complete interpretation as you too can also go between the two different datasets that we have used and come to your own conclusions.

Although I may not have a full understanding of Rapa Nui archaeology, I do have a fairly high expertise in the digital technology that was used within our investigation. I can say with a high certainty that the results shown are the most accurate and most complete investigation ever completed on the Hoa Hakananai’a statue. I spent many months going through these datasets to find hard to see details, making sure that any results were checked many times. I have used theses technologies on a range of different items, from prehistoric through to Victorian times, from small to large objects, and I have been lucky enough to work all over the world doing this. The technology stands firm in every instance and provides clearer results than previous methodological approaches. It is therefore hoped that with the inclusion of the original files that this too will provide a further insight and clarification to the full published record that we have presented over the last year. We will discuss our results in yet further in the new television series “Treasures Decoded” which will be broadcast September 10th on More4 (in the UK) and via the History Channel. In the meantime please carefully view the results shown below and please do get in contact with us if you see anything that we have missed!

The following RTI files are of the same resolution as those used within our investigation. Each of the following links are of the separate RTI files and are accessible through a web RTI viewer produced by the Visual Computing Lab in Pisa, Italy.

Front of the Statue

Lower Back of the Statue

Middle back of the Statue

Top of back of the Statue

Back of head of the Statue

 

For our highest resolution online model please visit this custom made website. Most online viewers limit the number of faces that can be included but the viewer (Based on 3Dhop) that I built loads partial amounts of the model based on your internet connection.

 

 

Conservation and computational imaging technologies

I’m Eleni Kotoula, a PhD student in the Archaeological Computing Research Group, University of Southampton.  I am a conservator of antiquities and works of art and I have worked in practical conservation since 2004 in museums and cultural organizations in Greece. My conservation research is focused on non-destructive analysis of archaeological material and accelerating ageing of adhesives/ consolidants used in …

Silver roman imperatorial denarius of Julius Caesar, CAESAR /Aeneas advancing to front, holding Palladium in palm of right hand and carrying father Anchises on left shoulder (O 19 mm), Archaeological Museum of Amphipolis, clockwise from top left: digital image, comparison between PTM (top) and a standard computer graphic approximation (below), normal map and RTI visualization in specular enhancement rendering mode (c) Eleni Kotoula
Silver roman imperatorial denarius of Julius Caesar, CAESAR /Aeneas advancing to front, holding Palladium in palm of right hand and carrying father Anchises on left shoulder (O 19 mm), Archaeological Museum of Amphipolis, clockwise from top left: digital image, comparison between PTM (top) and a standard computer graphic approximation (below), normal map and RTI visualization in specular enhancement rendering mode (c) Eleni Kotoula

I’m Eleni Kotoula, a PhD student in the Archaeological Computing Research Group, University of Southampton.  I am a conservator of antiquities and works of art and I have worked in practical conservation since 2004 in museums and cultural organizations in Greece. My conservation research is focused on non-destructive analysis of archaeological material and accelerating ageing of adhesives/ consolidants used in conservation.

I hope you agree that many interesting finds, covering a variety of materials and artefacts types have been presented so far in the course. In Week Five processing (Processing the finds) and registering of finds (Registering the finds) are discussed. What’s next? Conservation!  But what is conservation? How does computational imaging assists study and conservation of finds?

The conservation of antiquities lies on the edges of the double function of artefacts as resources for archaeological and historical information and as displayable objects, while it attempts to pace the rate of the processes of decay, minimise the deterioration effects and prevent alterations and damage. The cornerstone of conservation is the requirement for long term preservation, balanced with the needs to investigate and interpret, access, use, display and reveal objects and their values.

Undoubtedly visual analysis is a milestone in conservation practice which seeks to provide data relevant to structure, manufacture, damage and use of the object as well as materials identification. All surviving evidence is examined in order to lead to conclusions regarding characterization of the object and its condition. The findings of the visual analysis determine the goal of treatment and treatment type (conservation decision making). The changes introduced during treatment, after discovery, and throughout the artefact’s museum life, not only in appearance (including geometry, colour and texture), but also in chemical structure, are among the most influential processes that determine the artefact’s future, and dramatically affect its interpretation. Remedial treatment has a direct influence on chemical and physical properties of the objects, while preventive conservation or environmental preservation activities affect the object indirectly, as they can change its condition by altering its environment.

Application of digital recording methodologies help conservators perform visual analysis, document and monitor the condition of artefacts and the conservation operations. A characteristic example is the application of RTI in ancient Greek and Roman coins before, during and after cleaning. Also, the integration of imaging techniques offers advanced alternatives to traditional conservation methodologies. Considering the objectives of a conservation project RTI and photogrammetry can contribute significantly in: prevention, investigation, examination and analysis, documentation, communication, dissemination and presentation.

RTI helps exploration of artefacts’ biographies by enabling advanced examination of manufacture and use evidence, decay and conservation operations. Integration of microscopy and RTI makes it possible to catalogue the shape and topography of the various components of artefacts at a microscopic scale. Moreover, the synergy of infrared imaging and RTI highlights the texture and three dimensionality features of the inner layer in case of painted surfaces and assisted the examination of documentary artefacts. In the case of translucent materials the transmitted RTI method is a useful complementary technique. Photogrammetry (as you have learned on the course in Photogrammetry and laser scanning of artefacts) can also be used for 3d digitisation, enabling virtual examination of finds and offering possibilities for virtual reconstruction of incomplete finds. Similarly to RTI, the integration of photogrammetry, multispectral imaging and microscopy provides useful information and enable the user to examine these features in 3d space.

For an introduction to conservation I propose The elements of archaeological conservation by Cronyn, J. M., & Robinson, W. S. published by Routledge. For an intoduction to conservation Imaging  you can have a look at The AIC Guide to Digital Photography and Conservation Documentation edited by J. Warda published by the American Institute for Conservation.

Open access resources for conservation
1. Canadian Conservation Institute
2. Institute of Conservation
3. The Getty Conservation Institute
4. Posts on the ACRG site about RTI 
5. We work very closely with Cultural Heritage Imaging who have many resources on RTI.

Annotating RTI data in 3d and 2d

I’ve been talking to a lot people in recent months about annotation frameworks for RTI and today’s introduction to the #rodeimagingevent (see Hembo’s blog post) has crystalised some of these. I was talking to @kathrynpiquette about annotation and I also tweeted a query to @iipimage about it. @portableant suggested annotorious (something that I know our current MSc […]

I’ve been talking to a lot people in recent months about annotation frameworks for RTI and today’s introduction to the #rodeimagingevent (see Hembo’s blog post) has crystalised some of these. I was talking to @kathrynpiquette about annotation and I also tweeted a query to @iipimage about it. @portableant suggested annotorious (something that I know our current MSc student Vassilis Valergas has been examining) and also openCanvas was suggested. Also @aboutgeo mentioned the freeform extension to annotorious developed by @portableant. We started talking about the idea of this being a geospatial problem rather than an image annotation problem and whether frameworks in online GIS were more advanced.

A hacking triptych: Rode retable on left, + 2 #rodeimagingevent hack groups huddled behind

A hacking triptych: Rode retable on left, + 2 #rodeimagingevent hack groups huddled behind

I think at the core of my interest is the potential for novel discoveries to emerge as a consequence of shared annotation in image space. So, as we envisage in our @ahrcrti project multiple annotations would be created online allowing agreement (and disagreement as proposed previously by @LenaKotoula !). We have been discussing annotation in general elsewhere (and as usual very closely with CHI), and the depositing of these annotations within our institutional repository and the Archaeology Data Service, so I will link that in to this post in the future. Here I will concentrate on some thoughts I’ve had around sketching and 3d annotations.

Back in 2010 we published an example of spatially referenced RTI data where we used standard camera matching approaches from graphical modelling to locate an RTI releative to a scanned object. One might also use a photogrammetric approach to cross-reference two or more RTI captures against eachother, with or without the intermediate step of generating three-dimensional geometry. In such an environment one might also interrogate RTI, photogrammetry, laser scan and every other form of data. I have previously proposed an interface like Photosynth for handling this form of interaction.

Still, whatever the end magical framework, I think the key factors are the affordances of the annotation environment. I envisage the following scenario:

Capture

  1. Capture RTI
  2. Capture a second RTI from a different position, which may simply be an adjustment of focal length
  3. Encode the information to derive a relative co-ordinate system in a standardised way within the RTI metadata – this would employ the EXIF metadata for recording the lens properties and IPTC for location and vector orientation; with these metadata one could derive the relative positions
  4. Transfer this metadata to all derivatives e.g. cropped RTI and snapshots, in order that these can be tied together.

Annotation

  1. Load the RTI into a web or standalone viewer of some kind
  2. Generate 2d annotations as usual, but crucially provide keying information to enable viewer settings to link to annotations. For example, you set the specular filter properties and then sketch on some points of interest, perhaps adding point annotations too. You then adjust the filter properties and add some more annotations. These could then be played back and bookmarked.

Integration

  1. Calculate a relative co-ordinate system linking these two datasets – note: the accuracy of this is not relevant here, only the ability to quantify (or estimate) the accuracy
  2. Optionally also bring in true 3d data
  3. Provide a visualisation showing cones in space representing the FOV of each RTI
  4. Load an RTI viewer canvas into this plane
  5. Visualise extant 2d annotations on this plane
  6. Allow annotation in the 3d environment. This would allow a sketch to begin with the vector point snapping to a point on one RTI plane and then jump to another RTI plane. In this case the metadata generated would need to capture the RTI viewer settings on all RTIs involved in this annotation process. So, with every new point you could capture the viewer settings. Interestingly one might choose to capture the viewer settings for the collection of RTIs as a whole that were visible at the point at which the annotation was created since these all have an impact on the annotations created.

Hmmm. Now time to think about what frameworks already exist. We are still working on our web RTI viewer which is structured around @iipimage but there is the great webGL RTI viewer already by Gianpaolo Palma. Anyway, soup has arrived at the #rodeimagingevent here in St Nicholas’ Church in Tallinn and the hacking continues. Not a bad way to spend a Saturday.

Papyrus RTI case study

The Derveni tombs discovered in 1962 close to Thessaloniki in North Greece are considered one of the most significant archaeological sites in northern Greece because of their numerous rich grave offerings and their important location in the ancient Mygdonian city of Lete, on the pass of Via Egnatia. The cemetery comprises seven graves, and according […]

The Derveni tombs discovered in 1962 close to Thessaloniki in North Greece are considered one of the most significant archaeological sites in northern Greece because of their numerous rich grave offerings and their important location in the ancient Mygdonian city of Lete, on the pass of Via Egnatia. The cemetery comprises seven graves, and according to the excavation publication dates to 320–290 BC. One of the most remarkable finds of the Derveni Tombs is a papyrus roll, discovered in the remains of a funeral pyre above tomb A, a cist grave full of bronze and clay pots, vessels, jewellery and small objects (Themelis & Touratsoglou, 1997). The Derveni Papyrus fragments examined are preserved sandwiched between two sheets of glass. As a result the material integrity is safeguarded and the undesirable material deterioration due to handling is limited. At the same time, the glass mount poses a barrier in the study of the papyrus and affects visual analysis negatively. One of the most crucial features for the correct perception of information revealed from visual analysis is the perception of three-dimensionality, which in case of the Derveni papyrus is limited because of the glass mount. Another problem is the completely covering or the back side of the fragments, due to the backing material, which limits considerably the study of the material aspects of the papyrus.

One glass mount was captured in the conservation laboratories of the Archaeological Museum of Thessaloniki with reflected and transmitted illumination and infrared radiation, resulting in a series of RTI files. The front side of the glass mount was captured with visible reflected illumination and infrared radiation at 720nm, 850nm and 950nm. The back side of the papyrus was captured with reflected visible light and infrared radiation at 850nm, as well as with trans illumination and trans irradiation at 850nm. Data capture in the infrared spectral region was performed using IR light emitting diodes (LED), which do not accelerate thermal degradation. Following the mainstream methodology for H-RTI data capture is not possible. The reflections of the flash on the glass mount result in unacceptable images. This phenomenon takes place only in wider angles, so only low illumination angle data were used.

Common problems discussed by scholars, such as the buckling of the surface, the different layers of text stuck together with indistinguishable edges and the necessary movement of the papyrus in the hands of the expert so as for the letters to be revealed due to the different reflectance properties of the matte ink and the shiny papyrus background can be solved with RTI visualization. The synergy of RTI, Infrared imaging and trans illumination-irradiation enhances the readability and assists the overall diagnostic examination of the papyrus, the examination of the manufacture techniques, the determination of its condition and its possible conservation needs. IR-RTI proved to be a more efficient methodology compared to normal RTI. Not only it gave impressive results and enabled the reading of black letters on the darkened papyrus material more effectively but also emphasizes the three dimensional characteristics of the object and consequently assists the papyrus examination. Apart from documentation, restoration activities, reassembling and arrangement of the fragments can be benefited because the features which aid such processes, the continuity of writing, the shape of the handwriting, the design, the damage, the criss-cross pattern, the original joins and overlaps appear enhanced compared to normal (visible) RTI and/or infrared imaging.

Derveni Papyrus Fragment RTI visualization

Derveni Papyrus Fragment RTI visualization in multi-light and specular enhancement rendering mode

Derveni Papyrus fragemnt RTI visualization. Comparison of renderings in visible (left) and IR spectral area (right)

Derveni Papyrus fragemnt RTI visualization. Comparison of renderings in visible (left) and IR spectral area (right)

The Derveni Papyrus fragment examined in this case study is stored in the Archaeological Museum of Thessaloniki.

Themelis, P., & Touratsoglou, I. (1997). Tafoi tou Derveniou. TAPA, Athens.

Burying the Digital

I am at Museums and the Web this week in Baltimore. I was sat next to @trinkermedia and we were talking enthusiastically about  the physical, tangible and the interactive digital (as usual). Over the last few years we have been digitising very large collections of cuneiform tablets and are mid way through developing an open source […]

Clay tablet (wikipedia)

Clay tablet (wikipedia)

I am at Museums and the Web this week in Baltimore. I was sat next to @trinkermedia and we were talking enthusiastically about  the physical, tangible and the interactive digital (as usual). Over the last few years we have been digitising very large collections of cuneiform tablets and are mid way through developing an open source Reflectance Transformation Imaging web renderer that will allow interaction with these on mobile devices and desktops. The plan is that we will deploy these via tablets and phones of various form factors in order that the gyroscope and the lighting hemisphere captured from a front camera can be used to provide a sense of placing the digital tablet in its physical surroundings more completely. So, my aim is that, for example, in a room with low lighting captured from the phone the main directional light source vector will be identified from the maximum brightness in a photograph from the front camera and the RTI relighting intensity will be scaled to match that brightness. Once set this orientation should allow the gyroscope to link movement of the tablet to the space within which the movement is happening, and in turn relight the virtual object in a contextual way. We still have a way to go but we have a good handle on the methods to employ. So, watch this space.

But back to #mw2014. Javier and I were talking about his work to repurpose Linked Data and also his interest in interactive forms. I have been reflecting on the continuing power of the physical artefact in my life as I finalise the @UoSFLPortus MOOC. I want the MOOC to provide digital experiences of Portus and artefacts, but I also want to encourage the students on the MOOC to make their own interactive objects (more to follow on this soon via the Portus MOOC blog) and also to visit museums collections near where to they live to provide another form of engagement, and finally to think how accessible, touchable objects in the home could stand in for inaccessible, curated artefacts. (We now have the beautiful work of Eric Brockmeyer to stimulate us!). The plan is for the Archaeology of Portus MOOC to have a subsidiary archaeological computing and digital museums flavour, via the blog. So we would be excited to work with others on this in the coming months.

Anyway, all this made me think about the other project that is big in my head at the moment – the @Ahrcrti project focused on the RTI viewer. In the last few weeks we have been doing some work on RTI archiving in collaboration with Cultural Heritage Imaging and @ads_update and @UniSotonLibrary – the plan is to enable an easy mechanism to embed RTI repository content in blogs and websites and to link specific annotations via DOIs so that threaded citation and conversation around the RTI interpretations can grow. Again, more on this soon.

The question here is, could we physically instantiate the RTI of cuneiforms so that a physical tablet might survive as the carrier for the information long into the future? I am fascinated by the possibility of chance discovery of the tablet, and the intersection of the tablet with a repository. If nothing else it foregrounds the 10 or 20 years quoted in many archiving strategies for research data. I could do the same for information from Portus, perhaps encoding a brick stamp in similar ways. If I drop a rugged tablet into the foundations of the Palazzo Imperiale it may not be discovered for centuries. How long would the device survive? And what connections would the device be able to make in the future? What should we encode on the device. alongside the object data?

Crowd annotation of RTI

As part of the on-going AHRC RTI FoF project for the on-line, open source RTI viewer we are working on development of a tool that will encourage scientific co-operation among cultural heritage professionals, being at the same time an enhanced dissemination and presentation tool. The artefact visualised in RTI form is not just a static […]

As part of the on-going AHRC RTI FoF project for the on-line, open source RTI viewer we are working on development of a tool that will encourage scientific co-operation among cultural heritage professionals, being at the same time an enhanced dissemination and presentation tool. The artefact visualised in RTI form is not just a static record of the artefact but it enables the museum professional to execute visual analysis virtually and the members of the public to experience views of the artefact in a superior way. In that sense the annotations transform the RTI file from a high-quality record of the object to an examination record. Its educational and scientific uses are extended and extra values are attributed not only to the RTI file but also to the visualised artefact.  The first step towards the development of annotated RTIs is the annotation box link which enables the addition of textual descriptions, outcome of the RTISAD project, while the latest release of RTI Viewer software includes useful features for annotations.

The annotated RTI can be virtually re-examined by other professionals and members of the public and the relevant data will be available on line, enabling easy and meaningful exchange of information. While the new viewer is under development the following provides some initial thoughts about such a framework:

  • The users/creators should not be anonymous and each one should provide his/hers affiliation and add a url for a personal web page, in an attempt to assist further collaboration between researchers and museum professionals.
  • Annotation, accompanied by relevant metadata, will be used in order to define, explain and characterize areas of the image.
  • Annotations and uncertainty (?): Annotations with question mark used in case a user is not sure about his/hers interpretation.
  • Like annotation option (!):  Annotations used in order to support an already published annotation. A like annotation may be followed by an explanation text, used in order to provide an insight on the issue discussed.
  • Disagree annotation option (X): Annotations used in order to express disagreement must provide reasoning and propose alternative interpretation.
  • References (R): Each annotation can have one or more reference commends and internal reference commends. These can be added by the creator or another user. Reference comment: a link to an online resource, book, paper etc. used in order to support an interpretation added as an annotation. Internal reference: links to other RTIs in the repository for comparison etc. or to other annotations.
  • Searching/filtering and sorting of annotations so as for the users to be able to find the annotations relevant to their research interests.
  • Sorting annotations: Annotations to be sorted according to author date etc. and if the user selects a specific area of the image the existing annotations of this area to appear.
  • Keywords: a list of all the keywords used in annotations to appear so as for the users to locate the info they are interested in.
  • References: a list of all the references used in annotations to appear so as to provide the user with a bibliography regarding the issues discussed in the annotations.
  • Contributors: a list of all users who created annotations.
  • Interface: Colour coding would be useful. Other interface ideas include showing most recent annotations, following particular people’s annotations etc.