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.
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.
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.
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).”
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]
Filed under: Commentary, News, Technology | Tags: Antikythera Mechanism, PTM, RTI
Tom is a long-time friend of CHI and has been an adviser and collaborator on many projects. Tom is best known as the co-inventor (with Dan Gelb) of Polynomial Texture Mapping (PTM) in 2001 while he was at HP Labs. PTM is the first form of Reflectance Transformation Imaging (RTI).
Tom has had a long research career in the fields of computer graphics and computer vision as demonstrated by his many published papers. He has frequently applied this work to cultural heritage material, most notably as part of the team that deciphered the Antikythera Mechanism. This groundbreaking work was featured in the NOVA documentary “Ancient Computer”
Filed under: Commentary, News, Training | Tags: glossary of terms, photographic terms, technical terms
Over the years we have received a lot of requests for a glossary of terms used in RTI, and we are happy to announce that a new “Glossary of Photographic and Technical Terms for RTI” is available on our website! It includes photographic terms you need to know for RTI, like “Depth of Field,” “Color Temperature,” and “Aperture.” Also included are technical terms from computer graphics and computer vision like “BRDF,” “Fitting Algorithm,” and “Phong Lighting Model.” We have included terms for file formats like DNG, XMP and TIFF, along with basics in multi-spectral imaging such as “Infrared” and “Ultraviolet-induced Visible Fluorescence Photography.” We also included terms related to keeping good process history in your RTI work, including “Digital Lab Notebook,” “ICOM-CIDOC,” and “Empirical Provenance.” We did our best to adapt the definitions for RTI users, and we also included a few notes and recommendations on photographic settings.
As always with our work at CHI, this project was a collaboration. Lots of folks offered terms they wanted to see defined, and some provided definitions. We especially want to thank Tom Malzbender for definitions for many of the technical terms; Yosi R-Pozeilov for sharing his extensive glossary of photographic terms; and technical writer Judy Bogart for pulling it all together. And finally, we had a wee bit of funding for this work from the Institute of Museum and Library Services, as part of a larger grant project in their 21st Century Museum Professionals grants. Much of the work was done through volunteer efforts.
If you value this kind of documentation, along with the free open source RTI software, please consider making a donation to help support it.
What an encouraging way to end 2013: our Annual Giving campaign raised almost twice as much as the previous year! Our donors’ continued support of Cultural Heritage Imaging (CHI) is both touching to us personally and vital to our mission.
Our donors’ gifts enable CHI to develop innovative digital imaging tools and practices and disseminate them to experts and students all over the world. Specifically, this financial support helps us complete software projects, like our recent release of the updated RTIViewer 1.1 and our update to RTIBuilder (coming soon). Donations also fill in the gaps in our funding so we can refine our training materials and develop new instructional programs. We are currently working on a new class in collecting high-quality, accurate, 3D models using a digital camera (stay tuned to learn more about that). CHI also engages in a variety of projects with museums and historic sites, and donor contributions allow us to keep our fees as low as possible for these projects.
In the long run, financial gifts support our many users around the globe who are working on cultural documentation in vital fields such as archaeology, computer imaging, museum and library sciences, natural sciences, and data archiving.
We are deeply grateful to our donors for their generosity.
–The CHI team
Filed under: Commentary, Guest Blogger | Tags: color card, Dan Kushell, gray card, grey card
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.”
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:
- • “Steel Wool” 2121-20
- • http://www.benjaminmoore.com/en-us/paint-color/steelwool
- • “Sterling Silver” 1461
- • http://www.benjaminmoore.com/en-us/paint-color/sterlingsilver
- • “Pelican Gray” 1612
- • http://www.benjaminmoore.com/en-us/paint-color/pelicangray
- • “Mouse” 928-58 (20% reflectance)
- • http://www.cabinetparts.com/p/formica-laminate-sheets-for-countertops-FORM928204X8
- • “Fog” 961-58 (30% reflectance)
- • http://www.cabinetparts.com/p/formica-laminate-sheets-for-countertops-FORM961104X8
- • “Folkstone” 927-58