Stacked (3 σ-clipped) images of stars in the range 3.5 ≤ G_Gaia ≤ 7.5 (the star brightness is decreasing from top to bottom) and for the grizY filters (from left to right). The white circles show the circular masks to account for the isotropic effect on the nearby sources, whose radii are calculated from the variation in source density. The radius dependence on star magnitude is modeled by equation (2). (Color online)