Cultural Heritage Imaging


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]



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

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

 



CHI Welcomes Tom Malzbender to the Board of Directors! by cdschroer
March 21, 2014, 4:02 pm
Filed under: Commentary, News, Technology | Tags: , ,
Tom Malzbender imaging a piece from the Antikythera Mechanism

Tom Malzbender imaging a piece from the Antikythera Mechanism

We are absolutely thrilled to announce that Tom Malzbender has joined the Cultural Heritage Imaging Board of Directors!

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”

Welcome Tom!



NEW: RTI glossary now available by cdschroer
March 16, 2014, 10:13 pm
Filed under: Commentary, News, Training | Tags: , ,

Glossary word cloudOver 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.



A big thank-you to our donors! by cdschroer
February 10, 2014, 6:36 pm
Filed under: Commentary, News

thank-you_banner

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



Feeling Gray? How about some Shades of Gray? by marlinlum
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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Behind the scenes: RTIViewer 1.1 release by cdschroer
December 6, 2013, 2:15 am
Filed under: Commentary, News, Technology

rti-viewer-interface-sm

We are thrilled to announce the release of the RTIVewer  1.1 software!

This update release includes the most asked for features in the RTIVIewer.  As with prior versions, this is free, open source software. We have been working with it for a while, and we are excited to get this out to everyone in the RTI community. I am most excited about surfacing all the numerical settings data within the interface.  Of course those numbers were in the software, but you couldn’t see them or work with them directly.  The new bookmarks and snapshots features take advantage of and keep track of these settings for you.   Read more about all of the new features and how to use them in the updated User Guide.

For those interested in the back story, here is how this release came about.

We had a tiny amount of money in a 21st Century Museum Professionals grant from the Institute for Museum and Library Services to pay for some software updates.  We really wanted to add the support for normal visualizations, as that is incredibly useful both as a visualization of the surface normal data and as a way to compare the calculated normals over time, or across related data sets.  We also heard over and over again that folks wanted to be able to get back to specific views in their RTI file. A significant amount of preliminary work for a bookmarks feature had been done by Leif Isaksen of the University of Southampton.  We picked up his work (with his volunteer help) and expanded it to include interface updates and also to save these details with snapshots.

We were able to procure the development services of Ron Bourret, a senior developer who was willing to do some part time work at a very discounted rate.  When the money for the project ran out, Ron volunteered his services to complete it.  We also had volunteer help from Gianpaolo Palma, of the Visual Computing Lab in Pisa.  Gianpaolo was one of the principal developers of the original version of RTIViewer. Then we had some testers, and time from the CHI staff to oversee it all, test it, prepare material for the documentation, etc.  To complete things, the fabulous tech writer, Judy Bogart, stepped in and updated the user guide, as a volunteer.   We had hoped to ship the release earlier in the year, but once it became a volunteer project, the work had to be fit in around other things people were doing, like travel and paid commitments.

While we are totally happy with and proud of the result, we know that the process can run faster and more efficiently when we have funding. Adequate funding is essential in these releases, even when we get incredible volunteer support.

If you use RTI tools, or if you think they are valuable – please support our efforts.  We suggest a donation of $50 per year for users of the tools and services, like the CHIForums. We are a small independent nonprofit organization and we rely on donations to help support this work. We  appreciate all donations, in any amount.

We accept donations any time, and right now through December 31, 2013 is our annual giving campaign. If you are in the US, your contribution is tax deductible. Thank you for your consideration




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