Number of sources per magnitude bins of 0.5 mag, from our database (black line) and the GLIMPSE sample (red line). The boxes in each row refer to the band indicated on the upper left corner. For the diagrams on the left column we used the sources detected in all four IRAC bands with photometric errors <0.3 mag, whereas for those on the right column we used all sources detected in at least the corresponding band (with photometric errors <0.3 mag in that band).