An experiment was performed that compared conventional small-aperture and image-based reflection spectrophotometry of paintings. The imaging system used a liquid-crystal tunable filter, resulting in 31 spectral bands evenly sampled between 400 and 700 nm and ranging in bandwidth between 10 and 60 nm. The small-aperture spectrophotometer had a constant bandwidth of 10 nm. Test targets consisting of chromatic and neutral samples of various colors and spectral properties were used to derive a calibration transformation between the two technologies. Three paintings were analyzed: Saint Jerome Reading by Alvise Vivarini, Murnau by Alexej von Jawlensky and Pot of Geraniums by Henri Matisse, all from the collection of the National Gallery of Art, Washington, DC. Average colorimetric accuracy varied between 2.0 and 3.2 ?E00 units and the average spectral accuracy varied between 1.0 and 2.1% spectral root-mean-square. Two drawbacks are that the imaging system has a high uncertainty at short wavelengths, and the spectral matches for samples with flat spectra are slightly worse than for other samples. Both limitations can be corrected by changes in lighting, the calibration target, and the method of deriving the transformation matrix. Nevertheless, the imaging system has the advantage of no moving parts and may not require image registration, making it well suited to perform scientific imaging of cultural heritage. Furthermore, the image-based spectra have sufficient accuracy for pigment identification and mapping.
Department, Program, or Center
Chester F. Carlson Center for Imaging Science (COS)
Studies in Conservation 50N4 (2005) 253-266
RIT – Main Campus