The effect of background on localization uncertainty in single emitter imaging

We analyze singe emitter localization at high background levels. Maximum Likelihood Estimation closely follows the Cramer-Rao lower bound for a wide range of signal photon counts and up to very large background levels. The use of an idealized Gaussian to fit measured spots that originate from freely and rapidly rotating dipole emitters appears to work well for all parameters considered. We also present a very practical closed-form expression that approximates the minimum achievable localization uncertainty excellently for all signal and background levels.