Comparison of UBVR photometry of giant HII regions in NGC 628 with a detailed grid of evolution models of star clusters

We present our UBVR photometry observations of giant HII regions in NGC 628 in comparison with a detailed grid of evolutionary models of stellar clusters to interpret the observed colours of young stellar populations in terms of IMFs and SFRs parameters and dust content. Observed colours are complicate functions of searched IMF, age, regime of star formation as well as chemical abudances and interstellar reddening. A content of database of observed properties is crucial to get significant results. To exclude age-reddening and age-metallicity degenerations we carried out UBVR photometry of 127 giant HII regions are star formation complexes (SFCs) with independently measured chemical abundancies Z and interstellar reddening in NGC 628 by Belly & Roy (1992).