Left panel: the CSP for an N-body simulation of a disc galaxy. Colour code refers to the frequency of star per bin shown in the companion right panel. Right panel: the histogram of DF for the CSP shown in the left panel. In this figure, one immediately captures the concept of DF described in the text. The characteristic peaks corresponding to MS and RGB stars are shown in yellow. The CMDs have the coordinates of the absolute magnitudes M_V and the colours M_V − M_I.