2023

Duma, Zina-Sabrina; Sihvonen, Tuomas; Härmä, Paavo; Reinikainen, Satu-Pia

Constituent rocks of Cultural Heritage monuments and buildings are of mixed mineral compositions. For materials with homogeneous color properties, colorimetric evaluation is a well-established task. The colorimetric similarity of heterogeneous surfaces is difficult to measure due to the uneven distribution of minerals with different colors. The present work proposes a methodology for color difference calculation, exemplified on granite samples. The methodology proposed includes a technique to divide the rock images into color profiles using multivariate analysis and clustering. The differences between rock samples are evaluated (i) in average color profile distances, (ii) in the tone difference, and (iii) in the color profile distribution on the surface. The method proposed is appropriate for in-situ measurements using widely available digital imaging.