Performance of the REFEXTENDEDNESS parameter (leftmost panel) and the RF classifier (left central panel), evaluated on the validation sample, as a function of the r-band magnitude, for the reference set. For both panels, the blue curves show the fraction of true stars correctly classified as stars (stellar completeness), while the red curves show the fraction of true galaxies misclassified as stars (galaxy contamination). The last two panels displays the performance of the RF classifier obtained by removing the REFEXTENDEDNESS parameter (right central panel) and by adding photometric uncertainties (rightmost panel) to the reference set.