Optical characterization of biological tissues is of real interest to improve medical diagnosis and in particular in the detection of precancerous tissues. The reduced scattering coefficient s and the absorption coefficient a are the most commonly retrieved coefficients. Some methods also allow to obtain the anisotropy factor g, but only few of them are non-invasive. We propose a new non-invasive method allowing the estimation of the anisotropy factor and the reduced scattering coefficient. This method is based on the image analysis of the Q-element of Stokes vector backscattered from the turbid medium. These Q-element images show specific patterns depending on g, and s is determined by the size of the patterns. Therefore the use of Fourier Descriptors (FD) on simulated and experimental data, to discriminate the specific geometrical features of the Q-element, enabled us to determine the anisotropy factor and the scattering coefficient