Spectral Imaging of Matisse's Pot of Geraniums: A Case Study

The accuracy of color image-acquisition systems is most often evaluated using test targets of uniform color patches imaged under optimal conditions. In artwork imaging, system performance is judged visually, comparing the art with images rendered for display or print. Because the surface properties of the art may not be uniform, the spectral properties of the pigments may be different than the test targets, the sizes may be different, renderings are often metameric to the art, taking and viewing lighting geometries may be different, and the museum observers are more experienced than scientists in judging color accuracy visually, color accuracy as determined on a visual basis may be quite different than target performance. Therefore, an experiment was performed where a spectral-imaging system, designed for scientific purposes under laboratory conditions, was taken to a museum and tested in its photographic and conservation departments. The work of art evaluated was Henri Matisse’s Pot of Geraniums. Spectral and colorimetric comparisons were made between in situ small aperture spectrophotometry and imaging. The average performance was 3.7∆E00 and 3.1% spectral RMS; this was similar to an independent verification target of typical artist pigments applied to a canvas board. Viewed in close up, this level of accuracy yielded reasonable color matching for images rendered for display and print. Viewed overall, the matching quality worsened, a result of using diffuse lighting during image acquisition. Renderings appeared “flat” and reduced in perceived contrast. This indicates that when creating an image archive for both scientific and visual purposes, it will be necessary to use both directional and diffuse lighting geometries.