Distribution of the relative error on the physical disk effective radii σ(h_e)/h_e as a function of h_e in bins of total galaxy absolute magnitude in the g band. Only 3 bins are shown as examples of the general behavior. The color of the points represent the type of plotted error (see text for details) and the lines are the corresponding linear regression. There is a trend of relative errors increasing with h_e for the raw errors (in red). The correction derived globally over all absolute magnitudes (in blue) reduces the bias, whereas the correction by minimization over 12 mag intervals (in green), actually erases it.