Cultural Heritage Imaging


Marlin Reflects: RTI Training and the Sense of Discovery
July 27, 2018, 3:37 pm
Filed under: RTI, Training, Workshops | Tags: , , , ,

marlin_lumMarlin Lum is the Imaging Director at Cultural Heritage Imaging (CHI) and a member of the CHI training team.

I thought I’d take a few moments to decode what it’s like to be an instructor in one of our RTI training classes. Like anything else, there’s a certain level of planning, intention, and positive enthusiasm that I expect from myself (and from anyone enrolled). I do my best to pass this on to everyone who elects to give us their valuable time. I truly enjoy teaching at this level. I see these training sessions as a unique opportunity to pass on my knowledge in a form that can help create conditions primed for discoveries as well as to make new friends.

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RTI capture with iPhone in tow to track one of those special photographic moments. (Aviator sun glasses optional.)

CHI RTI training (as well as our photogrammetry class) simply means spending four days conveying photo DIY geekiness to a usually very enthusiastic, and sometimes even rowdy, motley crew of professors, scholars, conservation professionals, archaeologists, and pro photographers. (By the way, just so you know, it’s usually the archaeologists and the pro shooters who can hold the most liquor.) All of these folks, and everyone who walks into one of our trainings, is ultra-talented, focused, and very motivated to succeed. As you might guess, this makes my job significantly easier as well as seemingly more important. At least the furious note-taking in most of my hands-on demos would lead me to think this. As I always state on day one, hour one: “I make it my goal to make you successful (at least photographically).”

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Got spheres? Get on the plane! Make sure those spheres are on same plane as the object. Place them carefully so they do not move and are always in focus.

Helping these trainees from the bus stop to the f-stop and along their way to making discoveries is not only a privilege but something of a rush. More than once I have witnessed the birth of an important discovery. I once watched a conservator realize that a Mayan lead ingot sitting on the bench actually had numerous coded “knot” inscriptions, though they were seemingly invisible to the human eye. RTI revealed this fairly matter of factly. I’ve heard the shriek of conservation staff as RTI revealed a previously hidden but somewhat “suspect” under-painting. I once heard an Egyptologist glyph expert read aloud, then carefully re-read, a good fortune spell. Apparently, the original person who had paid for the spell got taken, because RTI revealed that the original owner’s name had been scratched away and re-etched with a new dude’s name. I imagine that was a fairly common event. Wait till the guy dies, then sneak over there, scratch out his name, and write yours.  Boom, check, all done, sweetie. All right there in stone — can’t deny that when the judge points a finger at you. The oohs and aahs I hear never disappoint.

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Setting up the object for proper RTI capture can take a bit of time, but using Live View mode can help your troubles go away.

Here’s the gist: I get fired up when I see you guys get fired up. RTI has the potential to inspire. Materials and objects that you didn’t think were worth imaging suddenly land on the request list. One down side: I heard a pro shooter from a large institution complain that he didn’t need any more work (oh, sorry).

Using the RTI Viewer to look at the details and stay detailed.

Use the RTIViewer to look at the details.

Just recently we taught an RTI class at the CHI studio (the photos in this blog are from that class). I’m not sure that any real discoveries were made, because we don’t have glyphs, ancient relics, masterpieces, or any “weird” non-provenance stuff from eBay lying around. However, I can vouch for the fact that I had a great time meeting cool new professionals, watching them engaged in what they do best, and then seeing them walk out the door, doing it better than before. Yup, I did write that. It’s in our best interest at CHI to make sure that you’re successful taking RTI (or photogrammetry) back to your professional crew.

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Behind the Scenes: Museum Photography at the Oriental Institute

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]



Greek red-figure vases, two surface examination methods and fabricated mock-ups

A linierhaar made of human hair is used to produce looped laid lines similar to that seen in Fig. 10 (left) (photo by Kari Kipper). A 3D elevation map of one such fabricated looped line displays topographical features distinctly similar to the ancient looped line (right). The threshold setting in the elevation map was adjusted to remove the majority of measurements associated with the cardboard substrate. The dimensions of the elevation map are 1.73 × 2.9 mm. The elevation scale bar is in μm.

Paula Artal-Isbrand and Philip Klausmeyer recently published an article in the Studies in Conservation journal.

Entitled “Evaluation of the relief line and the contour line on Greek red-figure vases using reflectance transformation imaging and three-dimensional laser scanning confocal microscopy,” the article examines “…the relief and contour lines on a group of ancient Greek red-figure vases and vase fragments.”

Paula and Philip, both of the Worcester Art Museum in Worcester, Massachusetts, USA, describe how they deployed “… two surface examination methods – reflectance transformation imaging and three-dimensional laser scanning confocal microscopy” to “… characterize the lines and answer questions regarding tools, techniques, and production sequence used by Greek vase painters.”

Their work is interesting and empirical, with numerous examples that yield detailed observations about the tools and techniques used to create the decorative features on vases and vase fragments, with a particular emphasis on relief and contour lines.

Download the entire PDF:

Evaluation of the relief line and the contour line on Greek red-figure vases using reflectance transformation imaging and three-dimensional laser scanning confocal microscopy

 



Feeling Gray? How about some Shades of Gray?
January 17, 2014, 7:05 pm
Filed under: Commentary, Guest Blogger | Tags: , , ,

Image

Feeling gray? How about some shades of gray?

Have a new studio? Want to paint it photographic neutral gray? Read on for important information and advice.

The information quoted below was authored by Dan Kushel, Distinguished Teaching Professor Emeritus at SUNY Buffalo State, New York, USA.

Recent photographic lab renovations at Buffalo State College required the walls to be painted a fresh coat of gray. Rather than randomly select a “nice” neutral gray, Dan Kushel took a more methodical approach.

Dan allowed us to share a PDF with the data that was produced from his careful research.

Download the PDF : neutral_gray_paint_laminate_reflectance_spectra-1

Commenting on his project, Dan stated:

“We used all three paints in the new conservation imaging laboratories which were just completed. The choice (of gray) depended on function.  The 18% N5 was used in the main photographic and reprographic studios; the 40% N6.5 in the image processing studio; and the 60% N8 for the chemical dark rooms and X-ray room.”

Testing the “spectra” was not a difficult process, and the “i1 and Robin Myers SpectraShop” tools were utilized to gather the data.

As noted in the PDF file, “neutral_gray_paint_laminate_reflectance_spectra-1.pdf,” the reflectance spectra of three neutral gray Benjamin Moore paints are fairly comparable to Munsell N5, N6.5, and N8 (18%, 40%, and 60% average reflectance).

The three are respectively: “Steel Wool” 2121-20; “Sterling Silver” 1461; and “Pelican Gray” 1612. Note that the neutrality of “Sterling Silver” is compromised above 650nm where reflectance sharply increases into the near infrared.  All spectra were made by averaging five readings of the surface.

The PDF also includes spectra of the N5, N6.5, and N8 patches on a new X-Rite ColorChecker for reference.

Also in the PDF are reflectance spectra of three neutral gray Formica laminates. They are: “Mouse” 928-58 (20% reflectance); “Fog” 961-58 (30% reflectance); and “Folkstone” 927-58.  Neutrality is quite good on all of these.

Reflectance spectra of the paints as applied to the walls closely matched the spectra of the samples we originally measured.  These paints should all still be commercially available.

Thanks to Dan for allowing us to share this great work!

********

Below are some links to the pigments:

Benjamin Moore

Formica laminates:

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Zero Out Settings
June 27, 2012, 9:01 pm
Filed under: Commentary, Training, Uncategorized | Tags: , , , ,

During the post processing phase, when you open your DNG files in Adobe Camera Raw (ACR), you have an opportunity to adjust your white balance and your exposure compensation. Prior to making these adjustments …

We recommend that you create a “Zeroed Out Settings” custom preset, and apply it to the entire image set. Consider making this your default preset for Adobe Camera Raw. To do this, set all of the settings to 0, then save as a named preset using the flyout menu for the Basic image adjustments panel. In particular, make sure all sharpening options are set to 0.

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Make sure that your Zero Out Settings match the above screen shot (click image).

Check the settings in all of the tabs. The first three tabs (Basic, Tone Curve, and Detail) have default settings that are non-zero; the radius setting on the Detail tab cannot be less than 0.5. In other tabs, default settings are already zero. (as taken from page 5 in the RTI Highlight Processing Guide v1.4)

‘Zeroing Out’ data ensures that your data is not being processed, interpreted or stylized to fit consumer tastes.



Reconnaissance. Scouting. Preparation.
June 22, 2012, 7:41 pm
Filed under: Commentary, On Location, Workshops | Tags: , , , ,

Reconnaissance. Scouting. Preparation.

Marlin Lum here. Imaging Director at Cultural Heritage Imaging. This blog entry inspired by Mark Christal, strong man and multi-media super genius employed by the National Museum of the American Indian (NMAI) at the Mall in Washington DC. It’s part of his professional game to find out as much as possibly about a topic and then present it to the public via modern visual technology. Go to the National Museum of the American Indian and check out what they are putting out in the world, really good stuff.

River Bed Pano

panorama photograph: scouting for rock art in a river bed

Mark is a graduate of CHI’s 4-Day RTI Training and a NCPTT Workshop participant where he not only refined his skills in RTI capture but also learned about photogrammetry. Aside from being a respected technologist and dedicated vegan, he is also an enthusiast of ancient Rock Art. (no- not album covers). Native American rock art.

Taking his Panorama and RTI capture skills in the field, (meaning a 14 mile mountain bike route, hot weather, lots of photo gear on back), Mark and his crew (also (former) NMAI super genius Video Master, Kevin Cartwright) entered the wilderness on a reconnaissance mission. Mission: to locate a petroglyph, shoot a Pano and scout it for future RTI capture.

I also have to mention, as stated by Mark, ‘that the park ranger had never heard of this (culture) site’. Mark and Kevin only found it after actively looking/hunting, and having followed a good tip from a kayaker. According to Mark, ‘this might be the only known on-site rock art in Maryland’. Mark goes on to say that, “The only other site (Bald Friar) was dynamited in the 20’s because it was about to be flooded.  Parts of that site are now spread across the state in a number of museums and culture centers”. Uhmm. Can you say, ‘sense of urgency’, get out there and document people!

A long time ago I used to work in Hollywood where I knew a location scout. It was his job to discover everything, everything about that location and bring that information back to the unit. His checklist asked questions like: Where is this on the map? What direction does it face? Where is the afternoon sun? Can I get a crew here? Do I need extension cords? Whats the scale of the artwork? What lens do I need? Is my tripod in dirt or water? Who’s land is this? What’s the deal with the roaming horned bull? (true story btw). And where is the crew bathroom?

You get my point. The more you know about your subject (and its owners {past and present}, the better). A thorough knowledge base about what exactly you intend to RTI is essential for creating a successful final product. It’s like anything else, knowing what equipment you’re gonna need (and what you don’t want to carry {or bike} for 14 miles) is gonna make or break it (your back that is).

Hollywood crews might research and setup a shot for months, only to have the actor whisper his lines in 40 seconds.

I will draw a conclusion to this blog and just point you to the large JPEG that Mark Christal email me from his Recon mission into the hot sun. (For those of you shooting in the comfort of a photo lab, you will have your chance.)

Mark’s Recon Pano gives us a glimpse into the beauty, the full shade during full sun, the water level during that time of year, the artwork and the scale (note calibration stick). And for those of you who are curious, yes, this location IS top secret, so, no use in hacking or looking. One last thought, shoot a capture when the water is running low.

Scout and be happy!

check out the flat pano image here on Flickr! Click on the Hi-Res image – can *you find the rock art? (look for the calibration stick)

Go directly to a large the jpeg: http://www.flickr.com/photos/markchristal/3938203809/sizes/o/in/photostream/



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

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/