Plotted as a function of μ, a) the noise level of the 720 s longitudinal magnetogram, σ⟨B_l⟩, b) the proportion of image pixels counted as containing significant magnetic activity, n_mag, c) the mean |⟨B_l⟩| of these points, ϵ_{|⟨Bl⟩| ,mag}, d) and the product of n_mag and ϵ_{|⟨Bl⟩| ,mag}. Left axes: the uncorrected (black series) and restored with K₂ levels (red series). Right axes: the quotient of the restored and uncorrected values (blue series).