K_S band luminosity functions (histograms; 0.5 mag bin width) for the various analysis steps to estimate both young foreground and the total Orion A population. Top left: comparison of the CF KLF with the Besançon model of the Galaxy. We find that a slight adjustment to all source counts in the model was necessary to fit the observations (see text for details). Top right: KLFs for the final survey catalog and the de-reddened data. Sources are mostly pushed to brighter magnitudes, however, we also allow (for statistical reasons) negative values of A_K and therefore find a minor population at fainter magnitudes than in the original histogram (the last bin starting at K_S = 20 in the de-reddened histogram). Bottom left: comparison of the de-reddened data with the scaled CF KLF. We clearly see an excess of bright sources, as expected from the young populations we find towards Orion A. Note here the good agreement of the CF and Orion A KLF for magnitudes fainter than K_S = 13 mag up to the completeness limit. Bottom right: comparison of the de-reddened Orion A KLF for point sources to the Besançon model. Also here we find a clear excess of sources caused by the young populations seen towards the molecular cloud. Both comparisons deliver similar numbers which is interpreted as a validation for our statistical approach.