Color perception of artistic paintings

Abstract

Museums use a variety of light sources to illuminate artistic paintings: natural daylight, tungsten halogen lamps, or light sources that approximate natural daylight, such as SoLux. Each type of light source has a specific spectral distribution and therefore produces a specific chromatic distribution for each painting. When choosing the illumination for their museums, curators have to consider, among other factors, the visual impression it produces when applied to paintings. The aim of this work was to use spectral data of artistic paintings obtained by hyperspectral imaging to determine psychophysically the correlated color temperature of the illuminant preferred by observers when looking at the paintings. We intended also to investigate how observers’ preferences correlate with the chromatic diversity of the paintings. Hyperspectral images of artistic oil paintings were taken over 400-720 nm at 10 nm intervals. The spectral digitalizations were carried at the Museu Nogueira da Silva, Braga, Portugal. The spectral reflectances of each pixel of the paintings were estimated from a grey reference surface present in the scene. The radiance from each painting under daylight illuminants of correlated color temperatures in the range 25000 K-3500 K was estimated and the corresponding luminance and chromaticity distributions computed. In each case, the number of discernible colors was estimated by computing the painting representation in CIELAB space and by counting the number of non-empty unit cubes in that space. In a psychophysical experiment using precise CRT reproductions of the paintings rendered with the set of daylight illuminants, the observers had to choose in each case the color temperature producing the best visual impression. The psychophysical experiment was carried out at the museum and the observers were selected from the museum visitors. It was found that the average color temperature selected by observers was about 6750 K, significantly larger than the one normally used in museums. Also, some correlation was found between the preferred colour temperature of the illuminant and the chromatic diversity it produced on the paintings