Spectral Imaging using commercial colour-filter array digital camera

Abstract

A multiyear research program is underway to develop and deliver spectral-based digital cameras for imaging cultural heritage at the National Gallery of Art, Washington, DC, and the Museum of Modern Art, New York. The cameras will be used for documentation, production imaging, and conservation science. Three approaches have undergone testing: a liquid-crystal tunable filter (LCTF) coupled with a monochrome camera, a six-position filter wheel containing absorption filters coupled with a monochrome camera, and a two-position filter slider containing absorption filters coupled with a color-filter array (CFA) color camera. The last approach is the most practical, as it uses conventional digital photography methodologies and equipment and can easily be incorporated into existing museum workflows. A virtual camera model was created that predicted camera signals from incident radiation and was used to design a pair of absorption filters. The filters were fabricated and tested using a commercial CFA digital camera. First experiments have been very promising: Average accuracy was under 1 CIEDE2000 and about 1.5% RMS for both calibration and verification data. This level of performance was superior to the authors' more complex approaches.