Cultural Heritage Imaging

Marlin Reflects: RTI Training and the Sense of Discovery by marlinlum
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.


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).”


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.


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.

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.


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

Capturing Reflectance Transformation Images by cdschroer
September 30, 2009, 1:52 am
Filed under: Technology, Training | Tags: , ,

By Debra Dooley, Executive Director, and Marlin Lum, Imaging Director, CHI

We have quite a bit of information on Reflectance Transformation Imaging (RTI) on our website. But what’s the process used to create a RTI? There will be several blog entries on the process. For more detailed information we recommend that you sign up for the Digital Imaging Techniques for Conservation & Education 3-hour workshop. Check out a Flickr photostream of one of the workshops.

There are four different parts to the process: Preparation, Capture, Processing, and Viewing. This blog entry is a high-level summary of the Capture process.

There are two different methods used to capture RTI. One is called Highlight RTI and the other uses a hardware system. CHI calls the custom hardware systems we build “RTI Capture Hardware Systems” and they are usually built for specific types of objects.

Highlight RTI

The highlight method is easy to use in the field as well as in a controlled setting. You use a tripod, digital camera, a light source (strobes or continuous lighting) and other generally available equipment. That’s one of the big pluses about highlight RTI —  “over the counter,” pro-sumer photographic equipment will yield professional, museum-quality,  high-grade digital RTI surrogates.

This picture was taken after one of the workshops. This is a classic “camera down” or “floor setup,” and is pretty basic. Basics include: a tripod with the camera mounted in the down position, a wireless trigger set (pocket wizards), a 580EXII flash strobe (with a string attached), and a priceless stone tool (insert your artwork here) in the field of view.

Carefully placed next to the object are two round black shiny reflective spheres. When the strobe hits the shiny surface, it produces a “highlight.” Bling! Bling! Software used in processing the images finds the highlights in each image to derive a light position (LP).

Also in this image is a Canon EOS Digital Rebel, tethered to a laptop and being controlled by the Canon EOS utility software. The blue tape minimizes movements and vibration during the capture process. The sandbag hanging from the ball head also dampens the wiggles. Again, though basic, the results are high tech.

Highlight RTI setup

Highlight RTI setup

RTI Capture Hardware System

The RTI Capture Hardware System is better suited to controlled settings such as in a museum conservation photo/lab. One benefit of using a rig is efficiency.  Think mass production, or in this case, mass-documentation. A RTI rig/dome is extremely favorable if one needs to document a large quantity of similar sized objects: coins, signatures, stone tools, paper samples, paintings, objects, etc. etc.

The most noticeable feature of an RTI Capture Hardware system is the light array — many lights (up to 40) mounted at different angles, all directed toward the center, at the object. And of course the camera is also mounted at the apex of the unit. A PC laptop controls the light sequence and asks the camera to open the shutter when a lamp is on, capturing the image with different light positions.

This capture sequence is  managed by open source software that we teach you how to use in our workshops, so you should look into it if this is interesting to you.

4-Day Training: Reflectance Transformation Imaging:
“Generating Digital Representations of Cultural Heritage Objects”

The following image is of a custom RTI Capture Hardware System built as part of the Developing Advanced Technologies for the Imaging of Cultural Heritage Objects project. CHI built 2 identical systems, one for the University of Southern California’s West Semitic Research Project and one for CHI.

Custom RTI Capture Hardware System

Processing the Images. After capture comes the processing of your images. Stay tuned for an update on that soon.