Effects of threshold fitting (Sect. 4.1.4). Mean relative error (black line) and standard deviation (yellow shaded area) for three simulations with different threshold values (0.0, 0.5, 0.9). Only pixels with normalized flux higher than the threshold values are included in the fit. Larger threshold values result in more accurate measurements for faint sources, at the expense of a systematic underestimation of the flux for brighter ones.