The visual impression of an artistic painting is influenced both by the colour and by the specific spectral structure of the rendering light source. The relationship between illuminant spectral structure and visual appearance assumes particular relevance with the advent of light sources with almost arbitrary spectral distribution, like modern LED based lighting. The aim of this work was to study, computationally, chromatic effects on paintings of illuminants with the same colour as D65 but different spectral profile. Hyperspectral data from twenty oil paintings were used in the analysis. A large collection of metamers of D65 was generated and the radiance reflected from each pixel of the paintings was estimated for each of the metamers. The number of discernible colours produced for each painting and illuminant was computed, and correlated with the spectral structure of the metamers. It was found that the number of colours generated varied considerably across the collection of metamers and that the metamers producing more colours were spectrally more structured, that is, less uniform. This result suggests that it may be beneficial to explore appropriate spectral tuning in practical illumination.

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The goal of this work was to evaluate the colour rendering of indoor lighting with CIE illuminants and white LEDs by estimating the chromatic diversity produced for normal and colour deficient observers. Reflectance spectra of a collection of scenes made of objects typically found indoors were obtained with hyperspectral imaging. Chromatic diversity was computed for 55 CIE illuminants and five LED light sources by estimating the number of different colours perceived in the scenes analysed. A considerable variation in chromatic diversity was found across illuminants, with the best producing about 50% more colours than the worst. For normal observers, the best illuminant was CIE FL3.8 which produced about 8% more colours than CIE illuminant A and D(65); for colour deficient observers, the best illuminants varied with the type of deficiency. When the number of colours produced with a specific illuminant was compared against its colour rendering index (CRI) and gamut area index (GAI), weak correlations were obtained. Together, these results suggest that normal and colour deficient observers may benefit from a careful choice of the illuminant, and this choice may not necessarily be based only on the CRI or GAI.

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