Two-dimensional histograms of the distribution of contaminant stars with , for gradient (top), Gaussian (centre), and binary (bottom) masks. The vertical axis indicates the differential P magnitude between the contaminants and their respective targets, whereas the horizontal axis indicates the corresponding Euclidean distances. The parameters used to calculate are δ_back, k = 0.8 mag, N_T = 24, n_tr = 3, and t_d = 4 h.