Selection dependence on X_FI,min, the Fisher discriminant threshold cut. X_FI,min varies from 2.0 (low densities, left) to 1.0 (high densities, right) with a step of 0.1. The sky region considered here is our ~50 deg² test area within the CFHTLS W1 field. Top panel: mean z_phot of the selection. Bottom panel: percentage of galaxies with 0.6 ≤ z_phot ≤ 1.0 estimated with the CFHTLS z_phot. The thin vertical line illustrates the 180 deg^-2 density used to set the Fisher discriminant threshold cut in Sect. 5.4.