The descr iptors c(k) describe the frequency contents of the curve: a value of k close to zero will describe low frequency information, an approximative shape, and the higher frequencies will describe details. For k = 0, c(k) represents the position of the center of gravity of the shape. This term is not interesting for the shape descr iption. Without this term, the descr iption won't be affected by a translation of the shape. The first frequency component, c(k) for k = 1, describes the size of the shape. If all the other components are set to zero, the shape becomes a circle (in fact, a N-sided polygon). One can use this component to normalize the set of Fourier descr iptors, so they remain constant after an homothety on the shape. The other frequency components will make alterations on the circle described by c(1). The descr iptors c(k) have opposite effects for positive and negative values of k: For positive values of k, the effect of c(k) is to “push” the circle at k–1 points periodically placed on the circle. This means the curve will be bent towards the outside of the circle at k–1 points. For negative values of k, the effect of c(k) is to “pull” the circle at 1-k points periodically placed on the circle. The curve will be bent towards the inside of the circle this time. The phase of c(k) is a rotation of this perturbation, which means it describes the place on the circle where the action is performed.