Bolometric correction as a function of near-IR colour. O-rich stars are shown as blue open squares and C-rich stars as filled red circles. Crosses are data for C-stars in the LMC and SMC from Groenewegen et al. (2009). The open black circles show the relation for Galactic C-stars from Bergeat et al. (2002), the lines are taken from Kerschbaum et al. (2010); the curved line is for C-stars, while the two straight lines define the region of O-rich stars.