Fig. 2

Example of building the training datasets. a Regions of interest selected in the The Nativity with the Annunciation to the Shepherds, Master of the Dominican Effigies, c. 1340, National Gallery of Art Miniatures 1975, no. 7, Rosenwald Collection. b The spectra of the brown ochre class collected from all four paintings showing the spectral variability. The black dotted line is the average spectrum for brown ochre