Accuracy of the flux determination in a simulation containing non-overlapping, PSF-shaped sources and “perfect” detection. Relative measured flux difference (f_meas − f_true) /f_true is plotted versus logarithm of the input flux f_true, for a simulated image populated with PSF-shaped sources (FWHM = 1.66′′). Each dot corresponds to a single source, with different symbols and colours referring to various diagnostics as explained in the legend and in the colourbar. The black solid line is the average in bins, the yellow shade is the standard deviation. The vertical dashed line shows the limiting flux at 1σ, f = 1. The inner panel shows a magnification of the brighter end of the distribution. The fit was performed on the whole image at once. See text for more details.