Lost fractions ΔF/F of the total true flux of ∼12 000 simulated galactic objects. The fluxes have been measured within elliptical apertures whose major semi-axis is equal to a given multiple fac_kron, min of the object isophotal semi-axis a. The solid lines show the median, the dashed lines the mean, and the dotted lines the standard deviations. The black line represents all sources, the red line only the bright (m <  24.5) sources, and the green line only the faint (25.5 < m <  26.5) sources. The dotted cyan curve corresponds to a full run on images where the observational noise was not included. Imposing , as typically done, yields a substantial underestimation of the flux. See text for more details.