Filed under: 3D, Equipment, Lighting, On Location, photogrammetry, RTI | Tags: Maori weaving, photogrammetry, RTI, TeRa
In January 2020 Mark Mudge and I traveled to the British Museum in London to document the only existing Māori canoe sail of its kind, made over 200 years ago. The imaging work was performed in collaboration with the New Zealand project Te Rā – The Māori Sail Whakaarahia anō te rā kaihau! – Raise up again billowing sail! funded by The Royal Society – Te Apārangi Marsden Fund.
The New Zealand team produced a 13½-minute video of the project that you can watch here: Imaging Te Rā at the British Museum 2020
helps prepare the sail for imaging
The construction and materials of the last known Māori sail, Te Rā, had not been identified, documented, or made publicly available, until this project put significant efforts into these identifications and documentation. Māori textile researchers from New Zealand brought in CHI to image the sail, which is made with fragile plant materials and feathers. The CHI team used both photogrammetry and Reflectance Transformation Imaging (RTI) to help the experts examine and understand more about the delicately woven and perishable materials. The research team wanted to gain a greater understanding of how the Māori sailed the ocean and the intricacies of their weaving techniques.
We worked with the sail on site at the British Museum for 5 days.
The first day was all preparation: meeting the team, examining the sail, setting up equipment, testing lights, and troubleshooting. The second day was spent on the imaging. The initial preparation had begun back in the CHI studio in San Francisco, when Marlin Lum, Imaging Director, prepared for the intensive imaging project by creating a life-size paper template of the sail so the CHI team could work out the imaging logistics ahead of time. Marlin had also created an ingenious camera rig to manage the imaging and protect the fragile materials. Marlin’s rig was attached to a rental pro video slider unit that we picked up in London on the first morning.
At the museum collection facility, the sail was spread out on a protective foam core platform on the floor, covered by black paper. Because the sail has a pattern of holes in it, we performed tests on how best to mask out the holes so that they would be correctly modeled as holes in the final model. The black paper worked best. Over this the team positioned the trolley with its cantilevered arm that could move across and incrementally shoot the entire area, photo by photo. The camera height could be adjusted using a slider and the camera angle could be adjusted using a ball head.
Here is my project note from the morning of the second day:
“Light tests and light adjustments are done. We add a Speedlite to the mix of lights to deal with a corner that was a bit dark. We will trigger the Speedlite (Michael’s Canon 600) with the PocketWizard TT1 and TT5 combo and all 4 Monoblocks are set to slave mode. It takes a bit of time to tune everything in using the light meter and small adjustments. We feel now the entire sail is evenly lit and imaging can begin.”
Scale bars were placed around the small end of the sail as were color checkers. Using a Canon 5DSR with 24mm f2.8 IS USM lens, and shooting at 18 inches distance from the subject, the imaging began with a calibration pass with 90-landscape-270 rows – then returned to the 90 position for the remainder of the imaging in that pass.
The feathers that trim the sail presented a significant imaging challenge: they stick up, and there are knots and places where the material juts out. The camera focus was set manually to allow some extra depth of field above where the main body of the sail was laid out, so that these elements would remain in focus.
As the work progressed, I recorded this:
“We completed the second pass of the sail with a 50mm lens today and shot 3 RTIs of detail areas chosen by Donna from the Maori textile team. Then we had a crew come in to turn the sail over, and we prepped everything for the back side (which is actually more important for the weavers). We will begin shooting that first thing tomorrow.”
Image: © TeRa Project, Marsden Fund, 2020:
After completing the work on site each day, we returned to our London apartment and began the next step: processing the images of the sail. We have built the RTIs and some other high-resolution 2D outputs of the sail and shared them with the team. The detail is fantastic. We look forward to the team’s continued research and the publishing of their findings, along with our imaging results.
Special thanks to: Donna Campbell, co-Principle Investigator (co-PI) for the research project worked closely with us on site; Julie Adams, Curator of the Oceania Collections at the British Museum, hosted the imaging project; Michael O’Neill, a photographer from the National Museum of New Zealand Te Papa Tongarewa; Kira Zumkley, a London-based heritage photographer and researcher; and Jill Hassell, museum assistant. Catherine Smith, co-PI on the project aided in logistics and overall project management.
You can read more about the sail in the research team’s blog and also the British Museum’s description of the sail from its online collection.
Filed under: Equipment, Guest Blogger, photogrammetry, Technology, Training, Workshops
Christopher Ciccone is a photographer at the North Carolina Museum of Art, and this is a post he wrote for the museum’s blog Circa. Chris attended the 4-day photogrammetry training class taught by the CHI team at the museum in May 2018 and describes the experience here. Thank you for sharing your blog, Chris!
Photogrammetry is the science of making measurements from photographs of an object (or in aerial photogrammetry, a geographic area). This is done by taking a series of carefully plotted still photographs that incorporate targets of known size and then analyzing the images with specialized software. The resulting data can then be used to generate a variety of output products such as maps, detailed renderings, and 3-D models for use in a number of applications.
Dense point cloud rendering of sculptor William Artis’s Michael. The blue rectangles represent the position of the camera for each image that was used to create the 3-D model.
Although photogrammetry as a scientific measurement technique has existed since the nineteenth century, it has been the advent of digital photography and high-powered computational capacity that has made it a practical tool for scholars, researchers, and photographers. Because photogrammetry can be employed on objects of any size, its usefulness in the cultural heritage sector is vast. Interesting uses of photogrammetry include, for example, documentation of historic sites that might be slated for destruction or are in danger of ongoing environmental damage.
Workshop participants in the NCMA Park photograph various angles of Ledelle Moe’s Collapse.
Photogrammetry at the NCMA
In May the Musem’s Photography and Conservation departments hosted instructors Carla Schroer and Mark Mudge from Cultural Heritage Imaging in San Francisco for a four-day photogrammetry training workshop. Participants included myself, NCMA Head Photographer Karen Malinofski, and NCMA objects conservator Corey Riley, as well as colleagues from the National Park Service and the University of Virginia.
Workshop participants Cari Goetcheus and Gregory Luna Golya photograph Willam Artis’s Michael on a turntable to facilitate views from all angles of the object.
William Ellisworth Artis, Michael, mid-to-late 1940s, H. 10 1/4 x W. 6 x D. 8 in., terracotta, Purchased with funds from the National Endowment for the Arts and the North Carolina State Art Society (Robert F. Phifer Bequest)
In the course of the class, we photographed several artworks in the Museum’s permanent collection, from a small bust by William Artis to Ledelle Moe’s monumental outdoor sculpture Collapse. The technique consisted of taking “rings” of overlapping photographs around the object, at optimal distance relative to focal length, with camera lenses set at a fixed focus point and aperture. The primary objective in each case was to establish a consistent, rule-based workflow in order to reduce the measurement uncertainty of the rendered photoset, which may then be used to generate reliable 3-D data as well as be archived and used for further study by others.
At the NCMA we plan to employ the technique for such projects as monitoring the surface wear over time of our outdoor sculptures, revealing surface markings of ancient objects for insight into makers’ techniques and tools, and generating 3-D renderings of delicate artifacts that can be manipulated and viewed in virtual environments by museum visitors and scholars. Other applications will become possible as 3-D processing tools are improved.
Will Rourk of the University of Virginia and NCMA Head Photographer Karen Malinofski photograph details of Collapse.
Christopher Ciccone is a photographer at the North Carolina Museum of Art.
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: 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, Equipment | Tags: breeze software, canon, capture software, focus, nikon, software, Technology
I was recently asked, ‘What DSLR camera is better for RTI data capture? ‘Canon or Nikon?’ The answer is like Godzilla Vs King Kong. Its gonna be a good fight.
The Short Answer is that either camera will work.
In the hands of a professional photographer, they are both very similar. The difference is the workflow – what you’re familiar with, what high quality lenses you own, and what equipment you’ve already got in your gear bag and studio ——— and what “Capture/acquisition Software” you decide to start a relationship with. (think Mind/Body – these two need to be pulling on the same oar)
Capture Software
Before you purchase a camera, you need to examine *how you’re going to interface with your DSLR when you’re shooting in *tethered* mode. Here’s the scenario, your stage is setup, your object is in place, you’re tethered to the camera via USB cable, and you launch your ‘capture software’ App. You need complete command of the basics : Composition, Exposure and Focus.
DSLR Remote Pro for Macs (Canon -> Mac)
http://www.breezesys.com/DSLRRemotePro4Mac/index.htm | http://www.breezesys.com/products.htm
The most stable Capture Software that we have used (bare in mind that we use Macs and Canons), is coded by a third party guy, Chris Breeze. He has taken the (Canon and Nikon) SDK and developed for a “combo” of Canon, Nikon – Mac, PC configurations. I’m not going to deep dive into the setups, but what I am going to state is that (at this moment in time), the Breeze software is stable, solid, is easy to use, and hardly *ever crashes. The user interface is Ok, a bit bare bones, but this tool gets the job done, and thats what we all want. Again, bare in mind that we use Macs and Canons (we have only used the Canon—Mac version). This software is installed on all our computers is our goto tool for image acquisition procedures.
The main user interface is a bit bare bones, but DSLR Remote Pro is solid and can handle minute focus adjustments needed for RTI production environments.
The last version of the Nikon Control Pro 2 software that I experienced worked really well, *except for the fact that it was difficult to check focus and scroll around bc that particular window has/had a restricted pixel size. It wasn’t as small as a thumbnail, but lets say that it did not take advantage of your screen size. All of the other functions were well behaved. Check it here: http://www.nikonusa.com/Nikon-Products/Product/Imaging-Software/25366/Camera-Control-Pro-2.html
The Canon Capture Utility (free with the purchase of a new camera) has a great interface, looks clean, works well, but it could be better, much better — it could be more stable. Sometimes it just flakes out and crashes. We used it for years with lots of happy moments, but towards the end we had a bitter break up. As RTI grew and we pushed the technology, we began to experience flaws. Specifically, with the ‘Live View Focus Controller functions’ (and its algorithms). Numerous frustrating crashes occurred when we asked it perform fine focusing adjustments in the ‘magnified mode’. This is pretty important considering that RTI *requires the subject to be in focus. Software crashes were even more problematic when we used a modified IR / UV camera — for some reason(s) that we can not explain, the software just didn’t adjust well to the different wavelengths of light under those conditions.
A few more comments:
If you use ‘good Glass’ (think prime lenses+superior optics) both the Canon and Nikon are going to get you professional results. We know many many Canon RTI shooters as well as a few Nikon shooters (and hasselblad-er(s). I think that the majority of users tend to be Canon. When we are asked to purchase equipment for client(s) we always steer them towards the Canon family.
With that said, I have seen professionals purchase a suite of Nikon gear and then *re-convert all the new gear and go to Canon. (and from ongoing conversations, they didn’t go back to nikon).
At CHI we’re Canon all the way.
Thanks for reading, Happy F-stop.
-marlin.
by Guest Blogger Eleni Kotoula, PhD student, University of Southampton, Archaeological Computing Research group
Application of normal and microscopic RTI to artifacts derived from the Hellenistic-classical Derveni cemetery in Macedonia, Greece, demonstrates RTI’s contribution towards prevention, investigation, documentation and communication. Microscopic RTI meets the conservation needs for limited human-object interaction, high quality and affordable visual analysis, advanced documentation and level of detail. Consequently, it does not only signal interesting developments of the technique, but also leads to its broader application in the cultural heritage sector and particularly in conservation practice.
Kotoula, E. And Earl, G. 2012. RTI and Conservation Practice, “Imaging in Conservation: Looking at artefacts under new light”: ICON meeting, Archaeology and Science Group, 10th – 11th November 2011, in STFC Rutherford Appleton Laboratory, Harwell Campus, Oxfordshire OX11 0QX. in press.
Cultural Heritage Imaging 