Standardized system for multispectral imaging of palimpsests

The Archimedes Palimpsest imaging team has developed a spectral imaging system and associated processing techniques for general use with palimpsests and other artifacts. It includes an illumination system of light-emitting diodes (LEDs) in 13 narrow bands from the near ultraviolet through the near infrared (Delta lambda <= 40nm), blue and infrared LEDs at raking angles, high-resolution monochrome and color sensors, a variety of image collection techniques (including spectral imaging of emitted fluorescence), standard metadata records, and image processing algorithms, including pseudocolor color renderings and principal component analysis (PCA). This paper addresses the development and optimization of these techniques for the study of parchment palimpsests and the adaptation of these techniques to allow flexibility for new technologies and processing capabilities. The system has proven useful for extracting text from several palimpsests, including all original manuscripts in the Archimedes Palimpsest, the undertext in a privately owned 9th-century Syriac palimpsest, and in a survey of selected palimpsested leaves at St. Catherine's Monastery in Egypt. In addition, the system is being used at the U. S. Library of Congress for spectral imaging of historical manuscripts and other documents.