Illustration of decontamination procedures on the sample cluster NGC 152. Left panel: selection of the cluster field and nearby contaminated field for NGC 152. The inner radius contains the selected cluster stars. The region outside the outer circle contains the selected field stars. The annular region in between the outer and inner radius is neglected to guarantee that the field is free of possible outer cluster stars. Middle panel: corresponding CMDs for the cluster region (within the inner radius). Right panel: corresponding contaminated field region (beyond the outer radius). The average grid sizes of ΔV = 1 and Δ(V − I) = 0.2 were adopted to better identify the CMD sequences of this cluster.