This paper deals with the measurement of color stimuli due to paint layers like the ones which are met at the painted works of art and more precisely at the byzantine and post byzantine icons. A new methodology is proposed in order to standardize and therefore facilitate the study of a multicolor painted surface, through a non destructive procedure. The proposed methodology is based on the correlation between the grey level values measured through an image acquisition digitizing system, on an experimental panel constructed according to the byzantine and post byzantine egg tempera technique and the tristimulus values obtained using a spectrophotometer equiped with an integration sphere.
The image acquisition is realised using a specially deviced vidicon camera and three optical filters, red, green and blue, alternatively mounted in front of the camera lens and chosen so that their spectral response simulates the color matching functions χ(λ), y(k) and ζ(λ) of the C.I.E. standard observer respectively. In order to perform an exact measurement of the grey level values a personal computer IBM AT equiped with a digitizing card PC-EYE- 1100 6 bit (64 grey levels) is used.
The relation between the grey level mean values measured for red, green and blue area of the spectrum, after an apropriate correction of shading phenomena and the tristimulus values X, Y, Z, is described by a linear function.