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Figure 1-21 shows an example of how the presence of ambient stray radiation can interfere with the interpretation of luminescence phenomena. The UV-induced luminescence image on the left Figure 1-21(a), was taken in the presence of some red ambient stray radiation. Figure 1-21(b) shows the UV-induced luminescence of the same subject where the source of this ambient stray radiation has been removed. Comparing these, it is clear that in Figure 1-21(a) the ambient stray radiation caused the dark areas in the image to appear lighter, the areas of ‘blue’ luminescence around the figure appears purple and the ‘yellow’ luminescence of the figure appears more orange. The ambient stray radiation observed in images such as Figure 1-21(a), can be considered as ‘background noise’ and, although this cannot be measured directly, it can be mathematically reconstructed and removed from luminescence images by post-processing methods, represented schematically in Figure 1-22 using a UV-induced luminescence image as an example. Figure 1-22. Schematic showing the correction of luminescence images for ambient stray radiation using a UV-induced luminescence images image of a detail from a wall painting fragment from the British Museum (Winged youth from the Tomb of the Nasonii, 1883,0505.5) as an example. Version No. 1.0 26 Date : 14/10/2013 NTH FRAMEWORK
