illuminating the tissue with a first light for exciting the fluorescent dye and includes a clock frequency given by a periodic sequence of illumination phases and dark phases;

separately acquiring first fluorescent images generated during the illumination phases by excitation of the fluorescent dye, and second fluorescent images generated during the dark phases by an illumination of the tissue with a second light;

correcting the first fluorescent images by subtracting second fluorescent images corresponding thereto; and

generating overall images by superimposing on the corrected first fluorescent images corresponding native tissue images which reproduce a tissue surface, wherein a number of second fluorescent images are acquired in a fashion following one another temporally during the dark phase, and

wherein, for the purpose of producing a second fluorescent image, at least one late fluorescent image acquired during a prescribed late time interval of the dark phase is subtracted from at least one early fluorescent image acquired in relation to a prescribed early time interval.