1. A method of segmenting biological cells in a picture, so that the biological cells represent a foreground of the picture, the method comprising: applying a first fast marching algorithm to the picture or to a pre-processed version of same so as to achieve a first fast marching image, the first fast marching algorithm starting from a background of the picture, and a velocity function of the first fast marching algorithm being based on a first edge-strength image of the picture; segmenting the first fast marching image or a further-processed version of same into a plurality of homogeneous regions; mapping each of the homogeneous regions to one node, respectively, of a graph so that nodes of adjacent homogeneous regions are connected to one another and so that the graph comprises roots which correspond to homogeneous regions located at cell centers; classifying, on the basis of the graph, each homogeneous region either as background or as foreground; and applying a second fast marching algorithm within the homogeneous regions classified as foreground to a second edge-strength image so as to segment the foreground into individual biological cells, the second fast marching algorithm starting from those homogeneous regions which correspond to the roots of the graph.