Lower panel: luminosity function in K_s for the stars in the giJHK_s photometry of IC 1613. The black solid line is the number of stars in the 0.065 mag bin, and the gray solid line is the completeness-corrected number of stars. Upper panel: the second derivatives of the observed and the completeness-corrected LF. The vertical dotted line at K_s = 18.2 indicates the detected magnitude of the TRGB discontinuity and its peak.