Measuring Shape Variation of Two-dimensional Outlines

An image-analytic technique that automatically determines the outlines for simple silhouettes is described. These outlines are numerically characterized using elliptic Fourier decomposition. Since the resulting Fourier coefficients can be normalized so that they are invariant to changes in magnification and rotation as well as other such transformations of the original silhouette, they quantify shape per se, and can be used as variables in multivariate analysis of form. In an application, discriminant analysis distinguishes between electrophoretically distinct populations of the mussel Mytilus edulis. While the technique was able to demonstrate an association between genotype and morphology, it was not able to identify reliably the population from which each specimen was collected.