Ridge detection is the attempt, via software, to locate ridges (or edges) in an image. In mathematics and computer vision, the ridges (or the ridge set) of a smooth function of two variables are a set of curves whose points are, in one or more ways to be made precise below, local maxima of the function in at least one dimension. This notion captures the intuition of geographical ridges. For a function of N variables, its ridges are a set of curves whose points are local maxima in N − 1 dimensions. In this respect, the notion of ridge points extends the concept of a local maximum. Correspondingly, the notion of valleys for a function can be defined by replacing the condition of a local maximum with the condition of a local minimum. The union of ridge sets and valley sets, together with a re