Stellar Population Synthesis is a technique for determining the types and rough counts of stars in a Galaxy based upon its spectra. Physics and heuristic techniques from observations of Stellar Populations and nearby galaxies enables creation of templates and rules (formulae) for estimating populations of distant galaxies based upon observable data.
Simulations of evolution of populations of stars are used to create models for the technique (Population Synthesis Simulation). Since Binary Stars make up a significant portion of the stellar population of a galaxy, including their evolution can increase the accuracy of such models (Binary Population Synthesis or BPS).
Stellar Population Synthesis Code