Filed under: Guest Blogger, On Location | Tags: Archaeology, knapped tools, lithics, RTI
This is the second post by our guest blogger Dr. Leszek Pawlowicz, an Associate Practitioner in the Department of Anthropology, Northern Arizona University, Flagstaff, AZ, USA. He can be contacted at leszek.pawlowicz@nau.edu. Thank you again, Leszek! Even in the age of digital photography, archaeology still relies heavily on old-school hand-drawn illustrations for documenting artifacts, particularly for publication. It can be difficult, or even impossible, to get a single photograph that shows all of the artifact’s key details. In my area of interest, knapped stone tools, low relief in small-scale surface topography, high relief in large-scale topography, specular (reflective) materials, variations in material color and contrast across the surface, all conspire to make these artifacts difficult to photograph. A skilled illustrator is capable of creating a drawing that reveals far more detail than even a good standard photograph (Figure 1). But creating such a drawing requires experience, time, and money, often making it impractical.
Figure 1: Comparison of digital photograph and line drawing of knapped stone tool. Courtesy Lance Trask, http://lktrask-media.com/.
Reflectance Transformation Imaging (RTI) is a great way to document and image knapped stone tools. The ability to interactively modify the lighting angle, as well as mathematically manipulate the perceived interaction of light and surface, allows the viewer to see details difficult to photograph. It’s almost the equivalent of having the object in your hands, and turning it at various angles to the light to reveal details of its structure and manufacture. However, one drawback is that you can’t embed an RTI view in a paper or publication unless it’s in electronic format. Also, unlike a drawing that can show all the critical details at once, you may have to move the virtual lighting angle in many different directions to reveal all details. Using data from the custom RTI systems I described in a previous post, I’ve been working on ways to create static images of knapped stone tools with detail comparable to that in a line drawing.
Figure 2: Modern obsidian knapped point. A – Original digital photograph; B – Static RTI view; C- RTI Specular mode; D – RTI Static Multilight mode; E – RTI Normals mode; F – Enhanced RTI Normals mode. Click on image for enlarged view.
Figure 2 shows a series of images of a modern knapped projectile point fashioned from specular black obsidian, a particularly difficult material to photograph because of its shininess and lack of contrast. 2-A is an original digital photograph, with the lighting coming from the standard upper left direction; while a fair amount of detail is visible, shiny highlights obscure some details, and the overall convex shape of the point interferes with lighting on the right side of the point. 2-B shows an RTI view with lighting from the upper left; while glossy highlights have been eliminated, and more detail is visible on the right, other details are somewhat more subdued in this static view. Figure 2-C uses the RTI specular viewing mode, which imparts an artificially shiny character to the surface. This is actually a superior result for this mode on knapped stone tools – most of the time, it doesn’t look nearly this good (as you’ll see shortly). But this image suffers from lack of detail in some areas, probably because of the artifact’s overall convex surface shape. Figure 2-D uses the RTI Static Multilight mode, where the RTI data is analyzed to determine the optimal blend of multiple light angles to reveal details. Once again, this is a better result than I usually get for knapped stone tools, but some details are still hard to see because of lack of contrast in many areas. Overall, I have found that the recently added RTI Normals viewing mode leads to the best results. This mode color-codes the surface based on the perpendicular direction at every point in the image. Figure 2-E was generated using the Normals mode and a second-order HSH RTI file (standard Polynomial Texture Mapping or PTM) files produce markedly poorer results). Even in the raw colored state, the amount of detail visible across the entire surface is vastly superior to the other views. Using standard image enhancement techniques, one can further process this image to generate an extremely detailed view of the artifact’s surface details (Figure 2-F). While this modern artifact was made of a difficult material, the freshness of manufacture, lack of wear, and non-exposure to the elements make the surface features quite sharp and easy to see. What about an actual prehistoric point with a real history?
Figure 3: Molina Spring Clovis point. A – Original digital photograph; B – Static RTI view; C- RTI Specular mode; D – RTI Static Multilight mode; E – RTI Normals mode; F – Enhanced RTI Normals mode; G – Slope-shaded mode. Click on image for enlarged view.
Figure 3 shows a series of similar photographs for the Molina Spring Clovis point, collected about 10 years ago in the Apache-Sitgreaves National Forest. Clovis points are approximately 13,500 years old; this one in particular has seen a lot of wear on the flake scars, making them difficult to make out. What’s more, the point’s material (chert) is slightly glossy and very light in color, minimizing contrast in surface details. Figures 3-A through 3-F show the same image processing sequence as Figures 2-A through 2-F; note in particular that the Specular and Static Multilight modes (3-C and 3-D) do not produce especially useful images for this point. The raw Normals image (3-E) brings up details difficult to impossible to spot in the previous images, and enhancing the Normals image (3-F) makes those details even easier to see. For Figure 3-G, a Matlab script was used generate a modified view based on slope; this brings out certain details not immediately visible in the original normals image. In my opinion, images like 3-F and 3-G are superior to standard digital photographs of knapped stone tools and could well be used instead of line drawings for publication purposes. Even in cases where line drawings are preferred, these images could provide a useful background basis for tracing artifact details, instead of drawing them freehand. Beyond static images, the normals data can be used to generate a full 3D representation of the artifact’s surface. Some examples of this are visible at my website, along with downloadable 3D files and RTI data files for several projectile points. The 3D surfaces aren’t yet fully accurate, as they can be affected by inaccuracies in the normals calculation, and error accumulations in the surface fitting. However, these results are already significantly improved from my initial efforts, and I will be working on improving them further. Even in the current form, I believe that it should be possible to extract usable information than can be used to quantitatively characterize knapped stone tools.
Filed under: Equipment, Guest Blogger, Lighting, Technology | Tags: capture, guest blogger, paste print, Reflectance transformation imaging (RTI), RTIViewer, specular enhancement
Our guest blogger is Dr. Lothar Schmitt, a post-doc in the Digital Humanities Lab at University of Basel in Switzerland. Thank you, Lothar!
For some people early prints are a boring topic, but a few specialists appreciate these crude woodcuts and engravings with their stiffly rendered religious subjects. There are reasons for this unusual predilection: Beginning in about 1400, prints became an increasingly important means to make images affordable for the general public. In addition, printing images stimulated the development of several technical innovations. Among these are ways to reproduce three-dimensional surfaces and to imitate the appearance of precious materials like gold reliefs or brocade textiles.
One such technique is called “paste print.”
Detail of a 15th-century paste print with numbered areas to denote materials used and damage.
With only about 200 examples existing worldwide, this kind of print is rare. It consists of a layer of a slowly hardening oil-based material (Fig. 1, No. 3) that was covered with a tin foil and brushed with a yellowish glaze in order to look like leaf gold (Fig. 1, No. 4). All these layers were stuck to a sheet of paper (Fig. 1, No. 1). To produce an image, the surface of an engraved metal plate was coated with printing ink and pressed into the paste. Through this process, the printing ink was transferred as a dark background (Fig. 1, No. 5), while the cut image of the metal plate generated a relief of golden contours and hatchings. Since these layers became brittle over time, most paste prints are heavily damaged (Fig. 1, No. 2). Moreover, the subjects they show are sometimes hard to decipher.
Traditional photographs are not well suited to reproduce paste prints because it is impossible to record the interaction between the light and the barely discernible relief of the print’s surface with one single capture. To document such effects, our team, a Swiss National Science Foundation (SNSF) research group of four people at the Digital Humanities Lab in Basel, Switzerland, made the decision to try Reflectance Transformation Imaging (RTI). The benefits of RTI are ideal for revealing the material properties of the prints. However, since RTI is not able to properly reproduce the gloss of a metal surface, we were unsure about the results. The first test was very promising.
We traveled from Basel to nearby Zürich, where there is a paste print of an unidentified saint glued into a manuscript at the Zentralbibliothek Zürich (B 245, fol. 6r). The library staff, among them Rainer Walter and Henrik Rörig, were very helpful. Peter Moerkerk, head of the digitization center, even made a high-resolution scan of this print that we could use as a reference image (Fig. 2).
Fig. 2: High-resolution scan of a paste print of an unidentified saint from manuscript B 245 in the Zentralbibliothek Zürich.
For capturing RTIs we constructed a Styrofoam hemisphere with a diameter of 80 cm. On the inside of the hemisphere, there are 58 evenly distributed LEDs that can be triggered in succession. The LEDs are synchronized via a simple control unit that is connected with the flash sync port of the camera. The control unit coordinates with the interval mode of the camera in order to capture a sequence of images automatically. The resulting RTI file shows the subtle surface texture and is instrumental for comprehending the relief and the layered structure of the print (Fig. 3).
Fig. 3: RTI of a detail of the print in Fig. 2, showing surface texture and layered structure.
As we pointed out earlier, the glossy effects of the golden parts appear too dull, but the “specular enhancement” feature of the RTIViewer helps to distinguish between the surface conditions of the different materials that were employed to make the print.
RTIs of two other paste prints in Switzerland and several others in German collections will be captured in 2015 and 2016. If you are interested in our proceedings, please see our web site: http://dhlab.unibas.ch/?research/digital-materiality.html
Filed under: Guest Blogger, Internship | Tags: cultural heritage imaging, digital humanities, history, scientific documentation
Our guest blogger, Matt Hinson, is a junior at the School of Foreign Service at Georgetown University in Washington, D.C. Welcome to CHI, Matt!
As a student majoring in International History, I’m interested in learning methods of interpreting history through the analysis of cultural heritage. Yet I’ve observed it is sometimes difficult to understand how to apply the knowledge I’ve gained through academics. As I learn more about the current threats to major historical sites and landmarks, I have come to realize that the documentation of world heritage sites is a major component of the effort to save them. And working to save the world’s historic and cultural treasures is a valuable application of historical research skills. So when I stumbled upon Cultural Heritage Imaging (CHI), an organization on the forefront of the scientific documentation of cultural treasures, I applied for a summer internship, and here I am.
As someone who would like to further pursue academic research in history, I have realized that learning how to study physical historical artifacts can add to my existing knowledge of how to analyze historical texts. Being introduced to the imaging methods that are featured here at CHI will improve my overall research skills in preparation for future projects. The emerging field of digital humanities is another area in which CHI heavily contributes. As the humanities become more and more connected with technology, I believe it is important that students of the humanities become better acquainted with such technologies. Learning about RTI, photogrammetry, and the other digital imaging methods developed at CHI is a great way to see how the field of the humanities can be transformed by such techniques.
This summer, I hope not only to learn from CHI but also to be useful to the organization in advancing its goals. CHI is working on a number of extremely interesting projects, and I would like to contribute to them as much as I can. I am not a technical expert when it comes to 3D imaging, so I intend to concentrate on expanding the cultural and historical dimensions of CHI’s work in world heritage preservation. I am very much looking forward to my time here at CHI!
Filed under: Equipment, Guest Blogger, On Location | Tags: Archaeology, canon, capture, dome, guest blogger, lighting array, lithics, Reflectance Transformation Imaging, RTI, stone tools
Our guest blogger is Dr. Leszek Pawlowicz, an Associate Practitioner in the Department of Anthropology, Northern Arizona University, Flagstaff, AZ, USA. He can be contacted at leszek.pawlowicz@nau.edu. A longer version of this post can be seen at http://rtimage.us/?page_id=27. Thank you, Leszek!
When I learned about Reflectance Transformation Imaging (RTI) back in 2009, one of my first thoughts was that it could be a useful tool for imaging and analyzing lithic archaeological artifacts, flaked stone tools in particular. Not an original thought even back then, and over the next four years I’ve seen the occasional RTI lithic image pop up on the web, demonstrating how useful RTI could be in this application. Early in 2013, I started experimenting with RTI on some modern replica projectile points using Highlight-RTI method. Though I got usable results with these experiments, I decided that Dome-RTI was a more appropriate method because of the reduced data acquisition and processing times.
So began a two-year process of building my first Dome-RTI system and refining it. After multiple iterations of the lighting system, controller, and camera/dome stand, I wound up with an 18″-diameter acrylic dome that produces excellent results and is useful for RTI on larger artifacts. However, it’s grossly over-sized for most of the artifacts I’m interested in documenting. Most flaked stone lithic artifacts in the American Southwest are less than 3 inches in length, and an 18″ dome is easily capable of imaging artifacts of at least 4.5″ in maximum dimension (I’ve gotten useful results on artifacts up to 6″ in length). What’s more, these artifacts are housed in scattered locations (museums, government facilities, universities, etc.), and the large size of the dome and stand make transportation and setup of this big system cumbersome. So, applying lessons learned from the first system, I built a second system with an emphasis on portability and speed (Figure 1):
Figure 1: Portable RTI dome
- Dome diameter is 12″, and sits on a stand that is 13.5″ square; total weight of the dome + stand + camera is less than 4 kg. The small size lets it fit into a Pelican case for easy transport.
- The controller box automatically lights 48 3W LEDs in sequence for the light sources; maximum current is 1 amp, and can be set as low as 150 milliamps. The camera shutter is triggered automatically in sync with the LEDs using either a wired remote cable, an IR remote signal, or a Bluetooth HID transmitter; a manual shutter mode is also available.
- Data acquisition time is about 3 minutes with a Canon S110 camera (12 MP, native 12-bit RAW), about one minute with Canon/Nikon DSLRs. A custom GUI front-end for the PTM and HSH fitters reduces data processing time to 1-3 minutes after the photographs are transferred to a computer.
- Dome is mounted on a hinged stand, which allows artifacts to be swapped in/out in about 10 seconds.
- Entire system is powered by 9-12V DC, either from a wall transformer or appropriate battery power supply.
The system can fit securely in a standard camping backpack with room to spare, with a total weight of less than 5 kg. The option of battery power makes this a truly portable, field-ready RTI system (Figure 2).
Figure 2: Portable RTI Dome “in the field,” north of San Francisco Peaks, Flagstaff, Arizona
When recording archaeological sites out in the field, it is often not possible to collect lithic artifacts to bring back to the lab for proper documentation. You either have to photograph them in the field (usually with less-than-satisfactory resolution of artifact details), or hand-draw the flake scars (a slow and tedious process, and often highly inaccurate). This portable RTI system makes it possible to thoroughly document lithic artifacts on-site.
This system has a few more tricks up its sleeve. Full analysis of a lithic artifact may require microscopic analysis of edgewear to determine how it was used.
Figure 3: Dome in microphotography mode with USB microscope
A simple reconfiguration of the system (Figure 3) allows high-magnification RTI imaging of lithic artifacts, using either the USB microscope (as pictured), or a DSLR equipped with a macro lens that has a working distance of 6″ or more (roughly 90-100mm focal length). A micrometer stage allows for accurate positioning of the artifact under the microscope.
You can also reconfigure the stand to mount the dome vertically for imaging larger artifacts. While I plan to use it in this mode to image the surface of Southwestern pottery, Figure 4 shows the system in vertical mode being used to image an oil painting.
Figure 4: Dome in vertical mode, imaging an oil painting
The normals may be off a bit because of the increased spacing between dome and painting, but you can still get useful results, like the specular mode image shown in Figure 5.
Figure 5: RTI specular image of painting surface shot in vertical mode
Total parts cost of this portable RTI dome, including the Canon camera, was well under $800. Scaling the dome up to a higher size would increase the expenditure by only the extra cost of the dome plus additional LEDs if desired (e.g. 64 instead of 48). For example, a one-meter dome with 64 LEDs would add approximately $400 to the total cost. In the near future, I hope to post information/instructions online that would allow anyone to build a system of their own. If I can build a system without instructions, I’m sure many others could easily build such a system with instructions.
In an upcoming post, I’ll present some of my lithics RTI imaging results from both of my Dome-RTI systems.
Filed under: Commentary, Guest Blogger, Lighting, On Location, Technology | Tags: capture, guest blogger, medieval, mosaic, Preservation, PTM, Reflectance transformation imaging (RTI), tesserae
Our guest blogger is Heidrun Feldmann, a PhD student in History of Art at the University of Basel and an assistant on the research project “Digital Materiality” at the Digital Humanities Lab there. Thank you, Heidrun!
It is obvious that art historians need good reproductions of works of art to do their research. However, photographic images, which are static and two-dimensional, are not capable of reproducing the visual impression we have when we look at mosaics. Their specific materiality and surface properties make a visualization of these characteristics difficult. Besides, as ancient or medieval mosaics are usually placed on the walls of churches, they interact with those specific surroundings. The lighting conditions inside these buildings, as well as the optical impressions for a visitor moving across the room, change dynamically, which results in a unique sensory experience. This is also a reason why the designs of mosaics in such religious contexts were often attuned to the liturgy. The impressive sparkling effect is caused by the surface properties of the countless tesserae, which – when animated by light − shimmer in many different colours and shine like precious metals. Sometimes those tesserae were placed in the setting bed with a certain tilt angle. This might seem irregular to us today, but then it was done intentionally to optimize the reflectivity of the surface.
With the aid of RTI (Reflectance Transformation Imaging), we now have more options for capturing and simulating the reflection properties of a mosaic’s surface, as well as its interaction with changing light conditions. The RTIViewer software enables us to convey the impressions of this highly dynamic medium to people who cannot visit the actual mosaic in situ. RTIs also help us document the current condition of mosaics more accurately than in the past, and they support our goal to answer questions about how light was used in medieval architecture.
To test the RTI method, we visited the Bode-Museum in Berlin, where a mosaic, originating from the church of San Michele in Africisco, Ravenna, is exhibited as part of the Early Christian and Byzantine Collection (Figure 1). We thank Gabriele Mietke, curator of the department, for allowing us to take our photos. The mosaic is fitted into the architecture of the museum, where an apse was constructed to imitate the original place of its installation in the church in Ravenna, albeit without the original lighting situation.
Figure 1: The team of the Digital Humanities Lab taking photographs of the mosaic at the Bode-Museum, Berlin.
Scholars have extensively debated the condition and state of preservation of this mosaic. Without going into all the details, we can say it is certain that the mosaic we see in the museum differs from the original of 545 AD because of its turbulent history. It has been restored and changed more than once, and some critics say that the whole mosaic is merely a copy. For us this was particularly interesting. We were wondering if the RTIs would provide further information regarding interventions, changes, or repairs.
Because of its size and form, it was impossible to take pictures that cover the whole of the apse. Therefore we captured it in twelve segments. About sixty photographs were taken of each of these segments, changing the position of the flashlight by hand for every picture. The twelve RTI files we obtained in this way show the reflection properties much better than any static photograph could do.
Figure 2: RTI image of the head of Christ in a detail from the mosaic.
Figure 3: Same detail of the mosaic with light from a different direction.
There are some limitations with glossy surfaces, because specular reflection cannot be adequately represented with the typical mathematical model used in Polynomial Texture Maps (the first form of RTI). However, changing the angle of the incoming light in the RTIViewer software allows us to identify areas whose structure and reflection properties differ from the others. In those areas the tesserae are of a different size or form and seem to be set in another way. All this suggests that these are the areas where the mosaic has undergone some kind of repair or restoration (Figures 2 and 3).
Having successfully tested the technique under the special conditions in the museum, we are now looking forward to the next step: capturing RTIs of medieval mosaics in situ and working on enhanced models for the visualization of gloss.
To find out more about our research project, see http://www.dhlab.unibas.ch.
Filed under: Commentary, Guest Blogger, News, On Location, Technology | Tags: ancient footprints, photogrammetry, Preservation
Sarah Duffy, PhD is a Postdoctoral Research Associate at the University of York in the Department of Archaeology. In May of 2013, after a series of storms, ancient footprints were revealed on a beach near Happisburgh (pronounced “Hays-boro”) on Britain’s east coast in Norfolk (see a 6-minute video). The footprints were fragile and washing away a little day by day. Sarah was called to the site by Dr. Nick Ashton, Curator of Palaeolithic and Mesolithic collections at the British Museum, to document it. Here is our interview with Sarah about this dramatic discovery.
Sarah shooting photogrammetry in the rain. Image courtesy of Natural History Museum, London, UK
CHI: Sarah, can you tell us how you got involved in the project and what you found when you arrived?
Sarah: It really came down to good timing and an opportune meeting of research colleagues. When the footprints were discovered, I had just begun working with Dr. Beccy Scott at the British Museum on a project based in Jersey called “Ice Age Island”. Beccy and my partner, Dr. Ed Blinkhorn, another early prehistoric archaeologist, have collaborated for many years, and he introduced us. During the week of the discovery, Beccy happened to be at a research meeting with Dr. Nick Ashton and suggested that he get in touch with me about the Happisburgh finding.
The next day, I received a call from Nick who asked if I would be able to take a trip to Norfolk to record some intertidal Pleistocene deposits at Happisburgh. Having just completed my PhD thesis (a “dissertation” in US currency), I was up for an adventure and ready to take on the challenge, and so I was on a train to the southeast coast two days later.
My first plan of action was to figure out how on earth you pronounced the name of the site! The next step was to figure out what equipment I would need to have available when I arrived. This proved somewhat challenging, as I had never visited the Norfolk coast, and it seems quite humorous in hindsight that one of the pieces of kit I requested was a ladder.
All of this said, the urgency to get the site photographed became clear when I showed up one very rainy afternoon in March. Standing on the shore, I felt very privileged to have been invited to record such an important set of features, which disappeared within only weeks of their discovery by Dr. Martin Bates.
CHI: What were your goals in the project and why did you choose to shoot images for photogrammetry? Can you tell us a little bit about your approach?
Sarah: Since I wasn’t sure what to expect when I reached the site, I took both photogrammetric and RTI kit materials with me. I intended to capture the 3D geometry of the prints with photogrammetry and subtle surface relief with RTI. However, when I arrived, both the weather and tidal restrictions limited the time we were able dedicate to recording. I therefore focused my efforts on photogrammetry, which proved a flexible and robust enough technique that we were able to get the kit down the cliff side in extremely challenging conditions and capture images that were used later to generate 3D models.
Based on the looming return of the tide and the amount of time required to prepare the site, our window of access was quite small. While I took the images, aided by Craig Williams and an umbrella, the rest of the team battled the rain and tide by carefully sponging water from the base of the features. As mentioned, I originally intended to capture images from above the site using a ladder. However, as the ladder immediately sank into the wet sand, I was forced to find other means of overhead capture: namely Live View, an outstretched arm, and umbrella. There was just enough time to photograph the prints, loosely divided into two sections, using this recording approach before we had to retreat back up to the top of the cliff (and to a very warm pub for a much deserved fireside pint!).
3D model of laminated surface containing the footprints at Happisburgh. Photo by Sarah M. Duffy
CHI: When you got back to your office, how long did it take you to process the images, and what software did you use?
Sarah: Originally, I used the Standard Edition of PhotoScan by Agisoft, later returning to the image set in order to reprocess it with their Professional Edition. PhotoScan’s processing workflow is relatively straightforward, and the time required to generate geometry is somewhat dependent on the hardware one has access to. The post-processing of the images was by far the most time-consuming component of the processing sequence. Since the software looks for patterns of features, there was a substantial amount of image preparation that needed to be completed first, before models could be produced. For example, rain droplets on the laminated surface that contained the prints needed to be masked out, as well as the contemporary boot prints that accumulated in the sand that surrounded the site throughout the image sequence.
CHI: How were the 3D models you produced used by the other archaeologists involved with the site?
Sarah: Once the models had been generated, the rest of the team, including Nick Ashton, Simon Lewis, Isabelle De Groote, Martin Bates, Richard Bates, Peter Hoare, Mark Lewis, Simon Parfitt, Sylvia Peglar, Craig Williams, and Chris Stringer, wrote the paper on the results. Nick Ashton and Isabelle De Groote closely analyzed the models of the prints in order to study size, movement, direction, and possible age of the early humans who might have created these features. Isabelle later worked with the 3D printing department at Liverpool John Moores University in order to have one of the digital models printed.
CHI: Since the footprints were washed away, your images are the best record of the site that exists. Are the 3D models accessible? What will you do to preserve this material?
Sarah: Coverage of the footprints, including excerpts of the digital models that I generated and the 3D printout, can be viewed at the Natural History Museum exhibit in London, Britain: One Million Years of the Human Story, which closes September 28th. Findings from the analysis have also been published in PLOS ONE, an open-access, peer-reviewed scientific journal.
As mentioned, when I visited the site last March, I had hoped to undertake a RTI survey. Although conditions on the day of recording did not permit multi-light capture, I have since been able to generate virtual RTI models that reveal the subtle topography of the prints. An excerpt of one of these models can be viewed on my website.
Additionally, the research team, in collaboration with the Institute of Ageing and Chronic Disease at Liverpool, are currently working on extracting further information from the image set. Findings from this work will be made available in the future. Once analysis is complete, the images and resulting models will be archived with the British Museum.
CHI: Thank you for your time, Sarah, and what a great story!
Sarah Duffy has been collaborating with Cultural Heritage Imaging (CHI), including taking CHI’s training in Reflectance Transformation Imaging (RTI) and working with the technique since 2007 while she was a graduate student in Historic Preservation at the University of Texas at Austin. Sarah authored a set of guidelines for English Heritage on RTI. During her doctoral work, she also began to apply her imaging skills in the area of photogrammetry.
We often get asked why we set up CHI as a nonprofit. I can understand the question, because we are doing some pretty high-tech projects, and we work with a number of famous institutions whose names people recognize, perhaps making us seem grander and better endowed than we really are.
There are a number of reasons why a “public benefit charity” structure made sense to Mark and me when we founded CHI in 2002. The greatest impetus for it was a personal vision we shared.
Mark and Carla at entrance to Dolmen de Antales, a Megalithic tomb in Portugal. June 2006
My background is in computer science, and I worked in software product development for years. At some point I had decided I wanted to apply my skills to “make the world a better place.”
Mark had similar leanings. His background was in philosophy and studio arts, primarily sculpture. He began looking into 3D modeling and laser scanning in the late ’80s, and by the mid-1990s he was teaching the subject. I had a minor in sculpture and ceramics. We both loved history, art, and archaeology. We had met in 1983 and married in 1989. By the late ‘90s, digital cameras were coming into play, and structured light scanning technology was becoming available for 3D capture.
Mark and I got fired up. We started seeking out people who worked in archaeology or museums to better understand their needs. Our first questions were: What did they wish to do that they couldn’t do in the field? Could the emerging imaging technologies help them in research and creating access to more cultural material?
Over time, and as we learned more, the seeds of CHI took root in us. By 2002 we began to imagine how existing and emerging technologies could be used to create robust, powerful, low-cost tools to document cultural heritage objects and collections. And so we formed Cultural Heritage Imaging.
Today, well over 10 years after we started our nonprofit, we remain committed to fostering the improvement, availability and adoption of these documentary tools. We see them as “democratizing technology,” because our vision is founded on making cultural and natural science techniques and materials available to people all over the world.
Many of our collaborations are only possible because we are a nonprofit. “Pulling on the same oar” for humanity’s benefit is a powerful reward. Our nonprofit status is attractive to top researchers and organizations who are drawn to work on and contribute to saving history. These experts are sometimes willing to help for very little money, and occasionally they even raise their own grant funding. Our open source approach is inclusive and allows others to add new features to the tools, moving the whole community forward.
The downside of this commitment to openness is there is a constant need to raise money, and much of the money we get is earmarked for specific purposes. It’s great to get funding for a project we want to do, like the National Endowment for the Humanities Start-up grant we recently received. However, many of the requirements of running the organization and fostering community growth are not covered by the grant funds.
Funding is critical! We get a lot of volunteer support, we work with students and professors, we get discount rates from many professionals. We are extremely grateful for this help and it makes an enormous difference. At the end of the day, we rely on the good graces of our donors to keep us, and the community, going.
I have had the good fortune to attend a few recent events that allowed me to see some really useful work other folks are doing in our field. I thought it worth a blog post to mention a few with some links. I’ll note that I have seen even more cool stuff, but if there wasn’t a paper or a page I could link to, I decided not to include it here.
First, Mark Mudge and I were at Computer Applications and Quantitative Methods in Archaeology (CAA) in late April in Paris. Yes, I know, it is a hard-knock life having to present your work in Paris in April. I always love CAA because it is a great conference for sharing information and real-life experiences. People are super helpful, and everyone wants to see everyone else succeed. This isn’t the norm for a lot of conferences.
Musee de Cluny, Paris
I want to point out 2 projects from there. The first is Eleni Kotoula’s RTI on Papyrus case study. New here is Eleni’s use of multispectral imaging and also her experiment with transmitted RTI. Eleni was interested in information for conservation about the state of this papyrus, which is mounted on cloth and under glass. The second project at CAA isn’t an RTI project, but it’s very cool and worth mentioning anyway. It is the work of Adam Rabinowitz et al. on PeriodO. As folks who follow our efforts know, we at CHI are big fans of metadata, process-history tracking, and related topics. Figuring out how to talk about periods in archaeology and art is really hard, and Adam and team have an idea for an interesting approach. This project recently won National Endowment for the Humanities support, so it will be able to go forward. You can and should contribute to this effort yourself!
Next up is the American Institute for Artistic and Historic Works (AIC) conference, which took place at the end of May, right here in San Francisco. It was great for us to have so many folks we have worked with here in SF. One of the things I noticed at this conference was that Reflectance Transformation Imaging (RTI) showed up in a number of talks, though that wasn’t the focus of the talk. RTI is another tool to look at objects people are studying, and RTIs are being shown right alongside IR images and X-rays and the like. YAY! My takeaway is that RTI is an accepted part of the practice for art conservators. We are super happy to see that.
Finally, I was able to attend a 3-day workshop on RTI current practice and future directions, hosted by the Cyprus Institute in Nicosia, Cyprus in early June. This was “All RTI, All the Time!” and it was very productive to be part of a dedicated meeting like this. There were many noteworthy projects presented there, and I’ll point out a few. Up first, the work of Todd Hanneken and others integrating spectral imaging and RTI. While many of us have done spectral imaging and RTI going back several years, what is new here is the use of a MegaVision monochrome camera system, and taking 11 spectral bands. RTI was shot in the visible and used for luminance data to generate the RTIs, and the color data collected via the spectral bands was then applied to the images shot in visible light. The team also tested shooting full RTIs in each spectral band for comparison. In addition, work from the Visual Computing Lab in Pisa for a WebGL-based RTI viewer, released in January of this year, was discussed. At the moment, this work is limited to streaming large RTI files and then allowing the user to pan, zoom, and relight, but some possible future directions were outlined. It is open source, so you can try it out yourself. There is also a project at The University of Southampton to develop a web-based RTI viewer, and we received an update on that project, but I don’t have a link where I can send you just yet.
RTI group in the old city of Nicosia
As part of the discussion on where RTI is going, there was a lot of interest in quantitative uses of RGB and normals data. There are a variety of people working in this area, though they didn’t present directly at any of these meetings. Several of these folks are working with us at CHI, and we are very excited by this direction. First up, the work of Dale Kronkright, Greg Bearman, and several others to look at tracking changes through normals, and also to quantify normal calibration. You can find both papers here. Additionally, there is great work going on at Simon Fraser University under Professor Mark Drew to improve the accuracy of surface normals calculated from RTI data sets. They are also working on improving the appearance of RTI data in the viewing environment. There are a number of papers on this topic, most recently the masters thesis of Mingjing Zhang.
It is an exciting time to be working with RTI data! There is much more work going on than I could include here, and more that hasn’t been published yet. I want to close with a plug for the CHIForums where many topics like this are discussed, and there is a Projects Forum where folks can put up links to their work, as well as get comments and feedback.
Filed under: Commentary, News | Tags: Anna Ressman, cultural heritage imaging, Digital Imaging, Oriental Institute Museum, Reflectance Transformation Imaging, RTI, Technology, University of Chicago, visualization
Recently Anna R. Ressman, Head of Photography at the Oriental Institute Museum, University of Chicago, shared a compelling article with me, and now I’m sharing it with you.
Here is a link to the Oriental Institute newsletter (PDF), which contains the article entitled, “Behind the Scenes: Museum Photography at the Oriental Institute.”
Anna describes the process in which five very different artifacts are documented, each with a unique challenge. And yes, you guessed it, one of those artifacts was documented using the RTI highlight method.
Documentation of the Egyptian stele “was photographed with a method of computational photography called Reflectance Transformation Imaging (RTI).”
Using RTI to photograph OIM E14655 with photo assistants K. Bryce Lowry and Austin M. Kramer
OIM E14655, Egyptian Stele, Limestone, New Kingdom, Medinet Habu, Egypt. 36x26cm
Specular enhancement using RTI of Egyptian Stele OIM E14655
Anna concludes the section on RTI with these insights: “RTI files can be created in such a manner that pixel data is analyzed to show specular information rather than color data, which can reveal more information about the surface of the object than color data alone (figs. 3–4). As you can see, the inscriptions on the stele are much clearer in the specular-enhancement PTM image (fig. 3), even though the studio photograph (fig. 4) was taken using a macro lens under controlled studio lighting. The former may not be as aesthetically pleasing as the latter, but it reveals much more information than would normally be seen — and that is just a single image out of a series of forty-five.”
Be sure to download the complete article and check out the rest of the newsletter as well.
Anna R. Ressman is Head of Photography at the Oriental Institute Museum, University of Chicago, USA. Anna is also a freelance photographer and a fine artist.
[Photos by Anna R. Ressman/Courtesy Oriental Institute Museum, University of Chicago]
Cultural Heritage Imaging 
Filed under: Commentary, Guest Blogger | Tags: Digital Imaging, Digital Preservation, Preservation, threats to heritage, world history
Our guest blogger, Matt Hinson, is a junior at the School of Foreign Service at Georgetown University in Washington, D.C. He spent the summer as an intern at CHI. Thanks, Matt!
Screen shot from ISIS video of the destruction of Nimrud, April 2015
During my summer internship at Cultural Heritage Imaging (CHI), I learned a great deal about the danger facing many of the world’s treasures as well as the efforts to save them. My background in international history leads me to believe that international law and policy can help to address many of the dangers. I have also learned how CHI is contributing to the revolution in how we interact with information and deal with these cultural heritage threats.
The variety of projects that CHI undertakes demonstrates the wide range of threats facing cultural heritage. Although some of CHI’s most recent projects have dealt with weathering and natural deterioration, it is important to understand the other risks to humanity’s greatest treasures. One can categorize tangible cultural heritage sites into natural formations, historic structures, including cities and sculptures, and inscriptions. Complex rock formations, the cities built by ancient cultures, works of art, and monuments are all included. It is also important to recognize cultural heritage sites that hold symbolic value to a specific community or group. Many of these are protected by national parks and museums, but only to a certain extent. Multiple forces continue to threaten this material.
Threats can be divided into man-made and natural. The man-made category encompasses destruction from conflict, construction, and development. Human neglect can also be included as a potential danger to the survival of important sites. War has become one of the most widely observed man-made threats to cultural heritage, particularly in ongoing conflicts in Africa and the Middle East. Groups fighting for ideological reasons, such as religious fundamentalists, have attempted to destroy artifacts that contradict their beliefs. The recent destruction of the ancient city of Nimrud by the Islamic State is one prominent example. Conflict areas tend to encourage looting of historic sites, leading to sales of antiquities on the black market. Often the lure of financial gain from the development of sites that contain important heritage outweighs the cultural value that is at risk. One example is the impending destruction of an ancient Turkish cave city after the completion of a dam that will put it under water.
In most parts of the world, environmental threats to cultural heritage are more prevalent than man-made ones. For monuments, statues, and other structures made of stone, weathering is a common means of loss. Precipitation, especially acid rain, and other kinds of exposure to water can lead to the gradual erosion of stone, rotting of wood, and general deterioration of sites and monuments.
National Park Service (NPS) map of the 105 US parks vulnerable to sea level rise. From “Strategies for Coastal Park Adaptation to Climate Change”: http://marineprotectedareas.noaa.gov/pdf/helpful-resources/webinar_beavers_schupp_nps_coastalcasestudies_111413.pdf
Environmental damage caused by climate change is accelerating the destruction. Rising sea levels are predicted to have a particularly devastating impact on many cultural sites. A recent study shows that predicted sea level rise over the next years will put 80% of Icelandic cultural sites at risk. According to the National Park Service (NPS), natural heritage sites in the US are also at risk. The NPS reports 105 parks as “vulnerable to sea level rise.” The effect on weather patterns due to climate change, particularly the increase in severe weather events, could pose major threats to cultural heritage sites beyond normal historical weathering.
How can these various threats be addressed? Archaeological preservation is one common method of physically excavating and preserving important historical artifacts. Moving objects to museums has successfully preserved different forms of cultural heritage throughout time. Digital imaging, practiced here at CHI, is a powerful tool to be used alongside archaeological methods to provide additional, more detailed information for the historical record. Digital representations of cultural heritage sites can be used to monitor the rates of change at these sites as well as preserve their shape and cultural significance. The re-creation of cultural heritage with digital methods also impacts how information is shared: an artifact that may be thousands of miles away can be viewed by anyone anywhere in an accurate digital form. This also allows objects and sites to stay in their original locations while providing access to their digital representations.
From my perspective, a crucial element in furthering the protection of cultural heritage is the legal and political protection of these sites. International law has developed to protect the things that have been identified as most sacred to communities around the world, including human dignity, life, and freedoms. Cultural heritage must be worthy of the same kind of protection every day as well as in wartime. Although some institutions already exist to defend cultural heritage, UNESCO, for example, I believe we must govern the protection of artifacts and sites with laws just as we do in cases of war crimes and sovereignty.
Another lesson I take away from my time at CHI concerns the changes in our interactions with information and knowledge. I am familiar with the usual media in our repositories of knowledge: text, photographs, video, and audio. While these media convey interpretations and descriptions of their subject matter, they rarely can stand as accurate representations of sites and objects. The potential that three-dimensional imaging brings to human interaction with information can be enormous. Many historical and cultural wonders previously limited to a particular geographical area could be made accessible to others, leading to progress in historical and interpretive research. Expanding research on these 3D methods, such as the ongoing work at CHI, can lead to highly effective ways of contributing to this revolution in information.
The Sennedjem Lintel from the Phoebe A. Hearst Museum of Anthropology at the University of California, Berkeley. Lower left left shows the surface color and shape. Upper right shows an enhanced surface shape.
CHI has exposed me to a lot of these problems facing world heritage sites but has also introduced me to the preservation and information successes that are possible with different methods and technologies.