Fig. 7

a, e, i Pictures showing the areas chosen as transmittance reference (in green). b–l) spectra comparison for the three selected colors (yellow, green, and blue) from acquisition #1 (b–d), acquisition #2 (f–h) and acquisition #9 (j–l). The bands’ position of the main chromophores (np = nanoparticles) are indicated with arrows, except for Fe²⁺. Since the maximum of the Fe²⁺ band falls outside the camera spectral range (1100 nm), and the NIR region is quite noisy, it was preferred to indicate the band width for this chromophore. The peak at 750 nm is an artifact probably due to the sunlight spectrum or interference from the atmosphere. Postfixs in curve labeling: l = left; r = right. Figure 6 shows the points where the spectra were taken