Distribution of the training sample’s surface gravities before and after the catalogue pipeline (described in Figure 4) is applied. The vertical line at log g=3.5 shows the separation used to validate the giants sample selection. The overdensity near log g~4.5 (orange region, right panel) arises from contamination by metal-rich turn-off and sub-giant stars in SEGUE, where their surface gravities overlap with the lower part of the RGB. Note that the log g<3.5 cut is an approximate validation threshold; a metallicity-dependent log g cut provides a more refined RGB selection.