An optimisation study of colour measurements on digitised slides of painted works of art

This paper deals with the problem of the colorimetric fidelity of digitised colour slides of painted works of art. A six‐matrix conversion model was derived that permitted the transformation of any RGB device‐dependent measurement on digitised colour slides to XYZ CIE 1931 device‐independent values. The model was calibrated against a reference colour chart. Eighty‐one uniformly‐painted colour samples were photographed together with a painting on a 4 × 5 inch colour slide that was digitised using a high resolution scanner. A 3 × 3 transformation matrix, of the corrected R, G and B values and the respective X, Y and Z tristimulus values provided by spectrophotometry, was calculated. The calculated matrix was then applied to a 13th century Byzantine fresco, captured on the same digitised slide, to transform the RGB measurements to XYZ CIE 1931 device‐independent values which were then converted into the L* a* b* CIE 1976 colorimetric system.