Computer Aided Colorimetric Analysis of Fine Art Paintings

In order to analyse paintings, specialists use many different techniques exploring different parts of the electromagnetic spectrum: near infra-red, ultra-violet, X-rays, etc. But surprisingly, the visual domain has rarely been analysed, probably because colour perception is a very complex domain, being rather difficult to analyse adequately by means of automatic techniques. Our visual sensations are the results of three different processes: physical, neuro-physical and psychophysical. Colorimetry is based on the evidence of trichromacy and the definition of a reference observer. It allows the measure of colours as luminous stimuli. For fine arts, it provides a way to quantify the paintings and their reproduction. The colours of a fine art painting is indeed a very important property of the painting. Traditionally, the colours have mostly been evaluated qualitatively by observing the painting. Besides the obvious uncertainty steming from the qualitative analysis, another important drawback with such methods is that it requires the curator or art historian to be located physically close to the painting. To perform a quantitative analysis of the colours of a painting, colour measuring devices such as colorimeters and spectrophotometers can be used. But, such equipment have a very poor spatial resolution, making it difficult to analyse the painting as a whole. We propose thus to apply digital image processing techniques to analyse the painting [1, 2, 3, 4]. However, to analyse and evaluate the colours in a painting it is important to be able to quantify them properly, in particular to make sure that the analysis is independent of the image acquisition device. In the next section, we present briefly a methodology that enables us to capture high-quality colour-calibrated deviceindependent images. Then, in Section 3, we proceed to the colorimetric analysis of three paintings.