Average unsigned vertical flux density vs. relative size (in pixel units) of the smoothing window, illustrated for two representative magnetograms, one obtained with 5-min integration (upper panel), the other with 1-min integration (lower panel). The solid curves represent the observed, noise-affected values B_app, the dotted curves the noise-free values B_ave, while the dashed curves are obtained through combination of B_ave with the noise σ according to the model described by Eqs. (3) and (4).