  We present an empirical method to derive photometric metallicity, reddening
and distance to old stellar populations by using a few major features of the
Red Giant Branch (RGB) in near IR color magnitude diagrams. We combine the
observed RGB features with a set of equations linking the global metallicity
[M/H] to suitable RGB parameters (colors, magnitudes and slope), as calibrated
from a homogeneous sample of Galactic Globular Clusters with different
metallicities. This technique can be applied to efficiently derive the main
population parameters of old stellar systems, in the view of using ground-based
adaptive optics and space facilities to probe the stellar content of remote
galaxies.
