1. A method of detecting an edge of a geological characteristic of a geological formation intersected by a borehole comprising the steps of, in respect of one or more signals obtained through operation of an image logging tool to energize the geological formation and thereby generate an image log of a length of the borehole, the one or more signals corresponding to and representing pixels of the image log, identifying locations at which the phase congruency of components of the one or more signals representative of data constituting the log or part thereof is maximal; and, in respect of such locations, characterizing them as one or more edges of geological characteristics.