Method of high spatial resolution imaging a structure of interest of a sample, comprising the steps: - selecting a substance from a group of substances which, by means of an optical switching signal, are repeatedly transferrable out of a first state with first optical properties into a second state with second optical properties and which may return out of the second state into the first state, wherein the substance is selected from a sub-group of substances which are excitable for spontaneous emission of fluorescence light by an optical excitation signal in the first state and which are non-fluorescent in the second state; - marking the structure of interest of the sample with the substance; - imaging the sample onto a sensor array, wherein a spatial resolution limit of the imaging is higher (i.e. worse) than an average distance between nearest neighbouring molecules of the substance in the sample; - transferring alternating portions of the substance into the second state by means of the switching signal; - exciting that portion of the substance that, at a time, remains in the first state for spontaneous emission of fluorescence light by means of the optical excitation signal; and - registering the fluorescence light as an optical measurement signal which is emanating from that portion of the substance that, at a time, remains in the first state by means of the sensor array; characterised in - that, in transferring the portion of the substance into the second state, an intensity of the switching signal is adjusted in such a way that at least 10 % of the molecules of the substance that, at a time, remain in the first state have a distance to their nearest neighbouring molecules in the first state which is higher than the spatial resolution limit of the imaging of the sample onto the sensor array, wherein the selection of the molecules to which this condition applies is based on transition probabilities; - that the measurement signal emanating from the molecules in the first state which have a smaller distance than the spatial resolution limit from each other is separated from the measurement signal emanating from the molecules at a sufficient distance, and that only in that case that a correspondence to a single molecule is given, a determination of the position of this molecule is made from an intensity distribution of the measurement signal over the sensor array; and - that, from a sum of the determined positions of the molecules of the alternating portions of the substance remaining in the first state, an image of the structure is obtained. - selecting a substance from a group of substances which, by means of an optical switching signal, are repeatedly transferrable out of a first state with first optical properties into a second state with second optical properties and which may return out of the second state into the first state, wherein the substance is selected from a sub-group of substances which are excitable for spontaneous emission of fluorescence light by an optical excitation signal in the first state and which are non-fluorescent in the second state; - marking the structure of interest of the sample with the substance; - imaging the sample onto a sensor array, wherein a spatial resolution limit of the imaging is higher (i.e. worse) than an average distance between nearest neighbouring molecules of the substance in the sample; - transferring alternating portions of the substance into the second state by means of the switching signal; - exciting that portion of the substance that, at a time, remains in the first state for spontaneous emission of fluorescence light by means of the optical excitation signal; and - registering the fluorescence light as an optical measurement signal which is emanating from that portion of the substance that, at a time, remains in the first state by means of the sensor array; characterised in - that, in transferring the portion of the substance into the second state, an intensity of the switching signal is adjusted in such a way that at least 10 % of the molecules of the substance that, at a time, remain in the first state have a distance to their nearest neighbouring molecules in the first state which is higher than the spatial resolution limit of the imaging of the sample onto the sensor array, wherein the selection of the molecules to which this condition applies is based on transition probabilities; - that the measurement signal emanating from the molecules in the first state which have a smaller distance than the spatial resolution limit from each other is separated from the measurement signal emanating from the molecules at a sufficient distance, and that only in that case that a correspondence to a single molecule is given, a determination of the position of this molecule is made from an intensity distribution of the measurement signal over the sensor array; and - that, from a sum of the determined positions of the molecules of the alternating portions of the substance remaining in the first state, an image of the structure is obtained.