(J − K_s) colour as a function of K_s for VVV CL074 based on the complete photometric catalogue (black points). Only stars within a radius of 0.7′ around the central position of the cluster are plotted. This radius was derived from the RDP calculated from the complete catalogue. The red dots represent the same CMD, but based only on the decontaminated catalogue. The stars in the grey area are undoubtedly not part of the cluster and can be removed from the catalogue without any loss of information before recalculating the RDP. Once a new and refined cluster radius has been determined from the RDP obtained from the filtered catalogue, a final statistical decontamination step was performed (see text).