Multispectral Search for Medieval Manuscripts

Analytical or computational imaging offers important new tools for scholarship in the humanities. Computational imaging technologies can support the collection of replicable data about cultural heritage objects that allow scholars and conservators to answer questions about artifacts that cannot be answered by means of simple visual inspection. YDC2 is supporting a project that will use multispectral imaging (MSI) of medieval manuscripts to provide additional data about the inks and pigments used in their creation as part of the Digitally Enabled Scholarship with Medieval Manuscripts project.

With invaluable support from Beinecke Library colleagues Ray Clemens, Curator for Early Books and Manuscripts and Chris Edwards, Head of the Digital Studio, last week Ruggero Pintus and Ying Yang, Post-Doctoral Fellows from the Computer Science department were able to multispectrally image the entire third recension of the Confessio Amantis,1392-93 by John Gower.  These images of the Gower manuscript promise to reveal additional information about how it was written and illustrated while the set-up process was important preparation for taking the technology on the road to other repositories of medieval manuscripts. Many thanks to the Beinecke Rare Book and Manuscript Library for supporting this work.

A multispectral image is one that captures image data at specific frequencies across the electromagnetic spectrum.   Spectral imaging can allow extraction of additional information the human eye fails to capture.  Multispectral imaging aims at providing a description of the reflective properties of a surface.  Multispectral images provide a more precise color analysis which makes these images suitable for the monitoring or restoration of artwork as well as any research activities that require high quality color information. – See more at: http://ydc2imaginglab.commons.yale.edu/#sthash.FPGLLoXx.dpuf

Ruggero and Ying explained that the entirety of the Gower manuscript was acquired with an 8-band, high-resolution multispectral camera and a Xenon light source that emits from ultra-violet to infra-red wavelengths, in a completely dark room. The raw data is a set of high dynamic range (16bit) images. The multispectral camera resolution is 2504×3326 pixels (8.3Mpixels), and for each multi-spectral acquisition we have eight images (one for each band).  This set-up has spectral sampling intervals (about 50nm) similar to those employed by Ricciardi et al. [1], which demonstrated that the limited set of pigments used in manuscript illuminations can be at least separated and sometimes identified, even when mixed, by acquiring images at moderate spectral sampling intervals (50 nm) under low light levels (∼150 lux) while having high spatial sampling (∼250 pixels per in). Thus, the acquired data will allow us to study the distribution of different elements across the manuscript page, to map out similarities in measured color/material/pigment, and to achieve the more robust, objective specification of them.

[1] Ricciardi, P., Delaney, J.K., Glinsman, L.D., Thoury, M., Facini, M. & de la Rie, E.R. 2009. Use of Visible and Infrared Reflectance and Luminescence Imaging Spectroscopy to Study Illuminated Manuscripts: Pigment Identification and Visualization of Underdrawings. In: L. Pezzati & R. Salimbeni, eds. Proceedings of SPIE, O3A: Optics for Arts, Architecture, and Archaeology II. Bellingham, WA: SPIE, vol. 7391, pp. 739106–12.

This is the setup used to multispectral scan a manuscript at the Beinecke library. The multispectral camera is mounted on a copy stand with a 1 meter column. The xenon light (UV) source is mounted on a separate tripod. Color targets are used to callibrate the camera. Once this is completed, the manuscript will be laid out on the copy stand and images of each page will be taken one at a time.

The color target and spectralon (white and grey target) are used to help callibrate the 8 multispectral camera filters: 6 in the visible range, 1 in the ultraviolet (UV) range and 1 in the infrared (IR) range.

This photo shows the manuscript open so the right pages can be acquired by the multispectral camera.

The manuscript is supported by foam as the book is rotated and the photographing of the left pages begins. A velvet ‘snake’ weight is used to the hold the right pages down so that they don’t move into the shots of the left pages.

This is a closeup of a section of the Gower manuscript.

This is a closeup view of some of the intricate scrollwork found in the Gower manuscript.

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