Input magnitude-size distribution of galaxies. The data points are the mean r_e as a function of I_E . Also shown are the standard deviation of r_e and I_E in each bin. The horizontal band denotes the PSF full width at half maximum and its variation across the field of view. A significant fraction of the galaxies have intrinsic effective radii similar to the PSF, especially at the Euclid wide field (WF) depth.