Fig. 4.

The mean spectrum of a selection of tiles as measured from each distance (cm) plotted against the spectrometer measurement of that tile, where each plot represents a new tile [labeled above it as corresponding to those in Fig. 1(b)] for both (a) quantitative and (b) relative data. At each distance, the data are balanced with either the correct Spectralon white reference image, the Spectralon reference obtained at 35 cm or the Spectralon reference obtained using a different light source.