1. A method of segmenting an image using a graph-based approach to image segmentation, comprising: providing an image; determining a first value of a segment parameter, wherein the segment parameter relates to a threshold function for establishing a boundary condition between a first segment and a second segment, wherein the segment parameter relates to a scale of observation in the graph-based approach to image segmentation; determining a first value of a similarity function configured to indicate a similarity between the image and its segmentation based on the first value of the segment parameter, wherein the similarity function comprises a symmetric uncertainty function; comparing the first value of the segment parameter and the first value of the similarity function to a predetermined function, wherein the predetermined function is a linear function representing a linear relationship between the log of the segment parameter and the symmetric uncertainty, wherein a value above the linear function indicates over-segmentation and a value below the linear function indicates under-segmentation; determining a second value of the segment parameter based on a result of the comparing; determining an optimal value of the segment parameter, the optimal value of the segment parameter comprising a value of the segment parameter that generates a segmentation of the image for which a difference between a corresponding value of the symmetric uncertainty and a portion of the linear relationship is minimized; and segmenting the image based on the optimal value of the segment parameter.