An improved single constant Kubelka-Munk method for pigment unmixing of Chinese paintings

Abstract

Since the mineral pigments on the surface of Chinese paintings are small in particle size and the pigment layer is too thin to cover the paper completely, their spectral mixing often shows nonlinearity. In this paper, aimed to accurately estimate the different types of pigments abundance on the surface of Chinese paintings, we proposed an improved single-constant Kubelka-Munk (KM) method for pigments unmixing algorithm. First, we selected Malachite, Azurite and Cinnabar pigments and mixed them in pairs in different abundances. They were added glue and then painted on the rice paper to produce the samples. The spectra of pure pigments and their mixed samples were acquired by the instrument of ASD FieldSpec 4. Second, we calculated the absorption and scattering ratio of the samples, pure pigments and rice paper. The rice paper and pure pigments were regarded as endmembers together for the pigment layer is too thin to cover the paper completely. The abundances were figured out base on the Fully Constrained Least Squares (FCLS) method endmember. Third, the abundances for different pigment endmember were re-calculated after removing the paper endmember. The experimental results show that the improved single-constant KM method has higher unmixing accuracy compared with the traditional spectral unmixing methods, and has good prospects for the application of unmixing composite pigments on the surface of Chinese paintings.