Cultural Heritage Imaging


Creating a Portable Dome-RTI system for Imaging Lithics by chicaseyc

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):

portable RTI dome

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).

Portable RTI Dome “in the field”, north of San Francisco Peaks, Flagstaff, Arizona

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.

Dome in microphotography mode with USB microscope

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.

Dome in vertical mode, imaging 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.

RTI specular image of painting surface shot in vertical mode

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.

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Behind the Scenes: Museum Photography at the Oriental Institute by marlinlum

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

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

OIM E14655, Egyptian Stele, Limestone, New Kingdom, Medinet Habu, Egypt. 36x26cm

Specular enhancement using RTI of Egyptian Stele OIM E14655

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]



RTI Experimentation with a Copper Breastplate in the Florida State Bureau of Archaeological Research by marlinlum

This is a Guest Blog by Photographer Joseph Gamble.

As an affiliate with the University of South Florida’s Alliance for Integrated Spatial Technologies, I traveled with a team of archaeologists doing imaging research and 3D laser scanning of artifacts to Tallahassee last year to work in the Florida State Bureau of Archaeological Research (BAR) and experiment with RTI on a number of Native American artifacts from Lake Jackson, Florida. AIST Directors, Drs. Travis Doering and Lori Collins along with AIST archaeologist Dr. Jeff DuVernay, helped me to manage a challenging RTI of a Native American copper breastplate as well as other copper and metal objects from Lake Jackson and several other Florida sites.

Native American copper breastplate from Lake Jackson, Florida

The artifacts were from the ancient Lake Jackson settlement, a civic-ceremonial center of a Mississippian chiefdom that flourished across parts of northern Florida between c. 900-1500 A.D. The breastplate (23 X 54 cm) was cold-hammered from a sheet of native copper and contains extensive iconographic and symbolic that today are faint and difficult to discern. In the 1970s, the piece was encased in a clear Plexiglas, cube-like chamber that had been infused with argon gas as a conservation measure to halt corrosion of the artifact. The reflective polymer barrier that enclosed and protected breastplate seemed to pose an insurmountable obstacle for its accurate high resolution documentation. To stabilize the breastplate it had also been pressed into a plaster base to prevent further fragmentation and distortion leaving the piece with a cracked or crenelated surface texture. This condition was an additional for the documentation because of the shadowing that further limited the usability of the image set.

To acquire an inclusive data set that would contain sufficient usable images to build an RTI, we placed the case on black velvet, mounted the black balls and commenced to shoot. The total image count came to 156 raw files of which 57 were used to build the RTI file and, much to our delight, it worked well.

View the Final RTI File by clicking here (you tube video).

Joseph Gamble is a previous 4-Day RTI Training graduate. You can learn more about Joseph Gamble Photography at: http://www.jcgamble.com/

You can learn more about the Alliance For Integrated Spatial Technologies at: http://aist.usf.edu/



Interview: James Coddington, Chief Conservator, Museum of Modern Art, New York by cwillen

CHI Executive Director Debra Dooley recently conducted an email interview with James (Jim) Coddington (JC), Chief Conservator at the Museum of Modern Art (MoMA) in New York. CHI is building a custom light array for MoMA’a Conservation Department to help with capturing reflectance transformation imaging (RTI) media of objects in the museum’s collection.

1. How long have you been at the MoMA?

JC: 23 years

2. As Chief Conservator at MoMA, are you constantly searching for new techniques to preserve and restore art?

JC: It is a necessity when conserving contemporary art in particular.

3. What are you doing to digitally document, analyze, and preserve the MoMA collection at present?

JC: We are using standard RGB imaging as well as multi-spectral imaging via a spectral estimation technique using a standard RGB camera with filters. We also maintain written digital documentation of treatments and other reporting.

4. Why have you decided to expand from what you are doing now into reflectance transformation imaging (RTI) techniques?

JC: The importance of 3D information in documenting works of art has been long recognized, mostly in the form of raking light photos. RTI gives us the means to collect substantially more 3D information in a standardized way that also provides data for scientific analysis of surface structure and topography.

4. Why did RTI interest you?

JC: I think mostly the demonstrated ease of use.

5. How will you use RTI?

JC: We will be using it initially to document texture on printed out photo papers but we expect to use it on many different types of objects in our collection.

6. A custom light array is being built for the MoMA. What objects will you capture first?

JC: See Answer #5.



Imaging Paper Squeezes With RTI at the Smithsonian by cwillen

By Guest Blogger E. Keats Webb

I mentioned briefly last month some of the objects that we have been using Reflectance Transformation Imaging (RTI) on here at the Smithsonian’s Museum Conservation Institute (MCI).  One project involved paper “squeezes,” paper pulp molds made from the surfaces of ancient monuments at archaeological sites.

In some cases these “squeezes” are primary resources containing rare intellectual and physical information from monuments that have deteriorated or sites that no longer exist.  Unfortunately, the fragility of the paper minimizes accessibility of these objects to researchers and scholars. This makes them great candidates for non-destructive documentation of the 3-D characteristics of their surfaces with the RTI method.

Senior Conservator, Melvin Wachowiak, and I worked with the conservators from a Smithsonian museum, imaging a couple of examples of paper squeezes to see what the RTI method might contribute in terms of preservation and research.

Since the squeezes are molds taken from stone inscriptions, the writing is reversed.  After the image acquisition we “flipped” the images using imaging software, and then processed the files so that the final RTI product could be a legible rectified document for researchers to study.

We found that the RTI method increases legibility through the combination of raking light features and the specular enhancement option while also creating a surrogate that can be more extensively “handled” by researchers and scholars. (See images below.)

We continue to use RTI on a daily basis and look forward to sharing more with you about how the method is helping the scientists and conservators within MCI and the Smithsonian for the research and preservation of the collections.

paper_normal_lite

Detail of Paper Squeeze with Normal Light Position

 

Paper with raking light

Detail of Paper Squeeze with Raking Light

 

Paper with specular enhancement

Detail of Paper Squeeze with Specular Enhancement



RTI @ the Museum Conservation Institute by cdschroer

By Guest Blogger  E. Keats Webb

Over the past three months I have been interning with Senior Conservator, Melvin Wachowiak, at the Smithsonian’s Museum Conservation Institute (MCI) exploring advanced imaging techniques for research and preservation of the collections focusing mostly on the Reflectance Transformation Imaging (RTI) method.  We started in September with an African leather shoulder bag, the RTI enhancing the faint tooling and degradation on the surface. In October we imaged a writing slate from the 1600s found in an archeological excavation of a well at the site of Jamestown, Virginia.  RTI proved an excellent tool in interpreting the drawings and writings that are found on both surfaces of the slate and at all orientations.  Other types of objects that we have explored include paper “squeezes” (molds taken from stone inscriptions), oil paintings, a jawbone, ebony and ivory inlaid cabinet doors and a daguerreotype.  We work alongside scientists and conservators on a daily basis at the Museum Conservation Institute, and RTI complements the studies happening within our labs along with other advanced imaging techniques used for research and preservation.

Set-up for the RTI of the Jamestown Slate.

E. Keats Webb left, Melvin Wachowiak right; Photo: Charles Durfor



On Location with an Anthropoid Coffin and the FAMSF RTI Capture Team by marlinlum
FAMSF_RTI_group_shot

Susan Grinols and her RTI capture team document an Anthropoid Coffin

In October 2009, Susan Grinols – Director of Photo Services and Imaging for Fine Arts Museums of San Francisco (FAMSF), assembled a team of scholars and imaging professionals to document an Anthropoid Coffin with the highlight RTI technique.

Sue and her team  members were thrilled with the final results. Using the RTI Viewer, suddenly, hard to decipher glyphs were clearer and easier to view. The curators, interpreters and conservators were shocked at how the RTI technology delivered so much detail, in a completely nondestructive manner.

For a brief look into the RTI capture session be sure to view the flickr gallery.