Colour-magnitude diagrams (J-Ks) versus Ks for sources in the random sample considering extinction-corrected aperture magnitudes. We present saturated sources as black diamonds, blended stars as blue open circles, and extended objects as red dots. Long-dashed lines correspond to the (J-Ks) = 0.95 mag colour cut adopted in this work. In the top and right panels, we plot the normalised distributions of colour and magnitude, respectively (short dashed line for saturated sources, long dashed line for blended stars, and red solid line for extended objects).