An improved method of calculating the rate of striation thinning for laminar flow in a static mixer has been developed. The shapes of the objects studied are reconstructed using elliptic Fourier descriptors, allowing discrimination between true changes in shape and noise due to discretization errors. The method also allows one to choose the level of complexity in the objects to be reconstructed which faciliates optimization of the computations without loss of information. The evaluation of the rate of striation thinning is based on local velocities giving a result closely related to the volumetric flow in different regions of the static mixer. (c) 2005 Elsevier Ltd. All rights reserved.