A method and apparatus are provided for obtaining a sub-resolution spatial information of a sample labeled with at least one type fluorescent label. The sub-resolution spatial information has localization information about the positions of fluorescent molecules of the at least one type fluorescent label in at least one spatial direction. The method acquires localization image data by employing fluorescence localization microscopy. The acquired localization image data is processed to obtain the localization information about the positions of fluorescent molecules of the at least one type fluorescent label in at least one spatial direction. The step of processing includes determining in each of the detected images of the series the positions of the barycenters of the detected fluorescence emission distributions from the single fluorescent molecules of the one or more fluorescent labels in at least one spatial direction.