Left-hand side: surface brightness profiles of the clusters M3, M13, and M92 over the entire extent of each cluster. Right-hand side: zoom into the central region of each cluster. Measurements based on star counts in the HST data are shown using green squares while blue diamonds represent the data of Trager et al. (1995). A solid red line shows the best-fit extended Nuker profile. For M3 and M13, we also show a Nuker profile with a core (i.e. γ = 0) as a dashed cyan line. The surface brightness profiles have been corrected for extinction.