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 twenty-minute introductory video is based on Hanneken's presentation to the
Society of Biblical Literature Digital Humanities Unit on November 23, 2014.

The goal of this project was to create a practical and effective procedure for the integration of two technologies that have emerged in the past ten years as the most powerful tools for imaging cultural heritage artifacts for conservation, reconstruction, study, and appreciation. 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. Although the desire had often been expressed and partial integrations had been attempted, the latest advances in spectral image processing had not previously been combined with RTI. The technologies are fundamentally compatible and complementary since spectral imaging is concerned with color rather than texture, and RTI is the converse.

The Integrating Project team tested two experimental integration procedures on three representative test objects. Humanities scholars evaluated the benefits and favored the simpler of the two experimental methods, which relies on narrow-band diffuse lights for chrominance information and a flash for texture information. The final results, along with the complete archive of images and processing scripts, are freely available for further study and application by scientists and scholars.

The procedures developed and tested will be beneficial to imaging a wide variety of artifacts for which both the chrominance information of spectral imaging and the texture information of RTI are important for scholars and conservators. 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.


[Supplement July 9, 2014] It is now possible to use the interactive images in a web viewer with the core interactivity (but not enhancements) of the downloadable viewers. The web viewer allows a quick overview of the capabilities of the integration of spectral imaging and RTI, while the product summary below facilitates comparison of older and experimental techniques.

The summary of images illustrates the benefits of the control and experimental procedures with tables of full-resolution thumbnails and links to large image and RTI files.

The project white paper describes the procedures and results in great detail.

The complete data archive (1.1 TB) is available online and on magnetic disk through the St. Mary's University library July 31, 2014. The data archive will be of interest to scientists who wish to experiment with additional processing techniques.

The ImageJ macros used for the project can be found in the file IntegratingMacros.ijm. Basic documentation appears in comments in the file.

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

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

Ken Boydston, MegaVision Corporation, President, specialist in digital imaging (

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

William Christens-Barry, Equipoise Imaging, specialist in spectral imaging and illumination (

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

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

Leta Hunt, University of Southern California, specialist in RTI and information management (

Kenneth Zuckerman, University of Southern California, specialist in RTI and imaging humanities artifacts (

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 or more images of the same object with the flash held at different angles. Using technology developed at Hewlett Packard Labs just over ten years ago, this series of 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 limits the color information to conventional at best.

  • - The InscriptiFact Digital Image Library
  • - West Semitic Research Project
  • - 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 Labs on RTI / PTM
  • - Smithsonian Institution
  • - Cultural Heritage Imaging

Updated November 29, 2014, TRH