Fig. 4

Comparison among IR reflectogram collected in the spectral band from 2100 to 2400 nm (a), image obtained from applying eq-1 (b), and the second principal component image (c) from the PCA analysis of the three IR reflectograms
Comparison among IR reflectogram collected in the spectral band from 2100 to 2400 nm (a), image obtained from applying eq-1 (b), and the second principal component image (c) from the PCA analysis of the three IR reflectograms