Integrating Spectral and Reflectance Transformation Imaging Technologies for the Digitization of Manuscripts and Other Cultural Artifacts

A project funded by the National Endowment for the Humanities to advance the tools that make visual objects accessible to humanities scholars

Project Description

This project will bring together the nation’s leading experts to integrate two proven technologies for imaging cultural artifacts. The first technology is spectral imaging, which excels at collecting detailed color information in order to recover information which is indistinguishable to the naked eye, such as unreadable text on a manuscript or stages of revision in a painting. The second technology is Reflectance Transformation Imaging (RTI), which captures the detailed surface texture of artifacts. RTI images can be viewed interactively and enhanced, allowing scholars and conservators to reconstruct the methods by which an artifact was produced and to analyze its current physical condition. The team will test two experimental integration procedures on three representative test objects. Humanities scholars will be responsible for evaluating the benefits. The work scripts and benefit analysis will be published for use in imaging major artifact collections around the world.

Although the desire has often been expressed and partial integrations have been attempted, the latest advances in spectral image processing have never been combined with RTI. The technologies are compatible in theory since spectral imaging is concerned with color rather than texture, and RTI is the converse.

The innovation will be of interest to any scholar of the humanities who has been frustrated by the limitations of conventional photography. In particular, this innovation project serves as the second phase of the Jubilees Palimpsest Project. That project will use the technology developed here to study a damaged 5th century copy of a work known from the Dead Sea Scrolls. Scholars will be able to recover unreadable text by enhancing erased ink and the impact of ink on the surface of the parchment. Similarly, scholars will be able to analyze the materials and methods behind paintings, textiles, and other crafts.

Products

The goal of this project is to create a practical and effective work script for the integration of two technologies that have emerged in the past ten years as the most powerful tools for imaging cultural heritage objects for conservation, reconstruction, study, and appreciation.

The summary of images produced by the Integrating Spectral and RTI phase is now available. Additional project will be available soon.

The primary product of this project will be a white paper reporting work script, evaluation of efficiency, evaluation of quality, and other lessons learned. The white paper will be disseminated on this and other websites by summer 2014.

The complete archive of captured and processed data will also be available to scientists who wish to experiment with additional processing techniques. Because all the images are perfectly aligned pixel-for-pixel (registration), the captured images can be better thought of as a data set, more than a series of pictures. It is difficult to anticipate all the ways scholars would want to mine this data. One possibility of interest for recovering erased text from palimpsest manuscripts is to apply Principal Component Analysis across a larger data set. That is, when our software tries to determine if a particular pixel is erased text or just mold, it will be able to consider not only which wavelengths of light it reflects, but also the warp and roughness of the leather which affect its reflectance properties. This is just one among many ways that a more complete, meaningfully aligned data set will open new possibilities for processing and visualization.

All products of the project will comply with open standards and will be freely available.

Participants

Todd Hanneken, St. Mary's University (San Antonio), Project Director, specialist in ancient Jewish literature (stmarytx.edu)

Michael Phelps, Early Manuscripts Electronic Library (sponsoring institution), Project Co-Director, specialist in spectral imaging and artifact handling (emelibrary.org)

Ken Boydston, MegaVision Corporation, President, specialist in digital imaging (megavision.com)

Bruce Zuckerman, University of Southern California, Project Co-Director at USC, specialist in RTI and ancient Near Eastern texts (usc.edu)

William Christens-Barry, Equipoise Imaging, specialist in spectral imaging and illumination (eqpi.net)

Roger Easton, Jr., Rochester Institute of Technology, specialist in spectral imaging and processing (rit.edu)

Marilyn Lundberg, University of Southern California, specialist in RTI and ancient Near Eastern texts (usc.edu)

Leta Hunt, University of Southern California, specialist in RTI and information management (usc.edu)

Kenneth Zuckerman, University of Southern California, specialist in RTI and imaging humanities artifacts (usc.edu)

Matthew Klassen, St. Mary's University, student researcher

Funded by the United States National Endowment for the Humanities.

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Spectral Imaging

Spectral imaging has advanced particularly over the past ten to twelve years on projects of team members, including the Archimedes Palimpsest, the David Livingstone Diaries, and the palimpsests at St. Catherine's Monastery in Sinai, Egypt. Although the term "spectral" is sometimes used when as little as one wavelength outside the visible spectrum (such as infrared or ultraviolet) is applied to an object, the current state of the art uses up to twelve different wavelengths. The human eye can only distinguish three fundamental colors, so the benefit of collecting data of such high color specificity is to process it using Principal Component Analysis and other technologies that enhance the image. For example, to the naked eye a given manuscript may just look like brownish leather, with traces of erased brownish ink, overwritten with more brownish ink, and corroded with brown decay. Yet, browns indistinct to the human eye can be distinguished by the particular spectral fingerprint of each material, and enhanced to make the contrast between materials clear.

Thus, unreadable manuscripts become readable, paints added in different periods become obvious, and corroded objects can be seen as pristine. For the most part, this method developed for flat objects with no major meaning conveyed by texture.

Reflectance Transformation Imaging

Unlike spectral imaging, Reflectance Transformation Imaging (RTI) uses a conventional camera and a conventional white flash, but is able to create rich texture data by capturing 36 images of the same object with the flash held at 36 different angles. Using technology developed at Hewlett Packard Labs just over ten years ago, these 36 images can be processed into a texture map which can then be visualized and enhanced in a number of ways. Using a special free viewer, one can interact with the object using a computer’s mouse as a virtual flashlight shining from any angle. One can also generate enhanced images that effectively remove color information in order to isolate and highlight surface texture. RTI technology is particularly useful for inscriptions in rock or clay in which the texture conveys the meaning. It is even possible to reconstruct the path of the scribe’s pen as the thickness of ink decreases with each stroke. The technology also excels at capturing and conveying other physical properties of the materials, their construction, and their conservation.

Although this technology has been used with infrared and other alternative wavelengths of illumination, it has never been integrated with the advanced spectral imaging described above. The use of conventional visible-spectrum cameras and xenon tube flashes limits the color information to conventional at best, and color information is often discarded in processing.

  • inscriptifact.com - The InscriptiFact Digital Image Library
  • usc.edu - West Semitic Research Project
    • usc.edu - Zuckerman, Bruce. "The Dynamics of Change in the Computer Imaging of the Dead Sea Scrolls and other Ancient Inscriptions." In Rediscovering the Dead Sea Scrolls: An Assessment of Old and New Approaches and Methods, edited by Maxine L. Grossman, 69-88. Grand Rapids: Eerdmans, 2010. Freely available online.
  • hp.com - HP Labs on RTI / PTM
  • si.edu - Smitsonian Institution
  • culturalheritageimaging.org - Cultural Heritage Imaging

Updated April 29, 2014, TRH