Figure 3
THz multispectral images obtained based on the components in frequency bands within (a) 0.1 and 0.5 THz, (b) 0.5 THz and 1.0 THz, (c) 1.0 THz and 1.5 THz, (d) 1.5 THz and 2.0 THz, (e) 2.0 THz and 2.5 THz, (f) 2.5 THz and 3.0 THz. Features associated with the inscriptions start to appear in the frequency bands above 1 THz, and images from the low frequency bands mainly reflect the surface morphology of the cross. All the images are normalized to their maximum pixel values.
