Fig. 2

Procedure for experimental noise estimation. Examples of experimental spectra with different noise level corresponding to 2–256 scans averaging (left). (middle) Presentation of band free region, with a fitted straight line, used for noise estimation. After baseline correction, standard deviation gives numerical noise value (middle). SNR presented as an average of results for sample region pixels (spectra), for datasets corresponding to the number of scans presented on X axis (right).