Stereo by correlation can be used to produce urban DEM without a priori knowledge on the shape of buildings, as opposed to feature-based methods. Nevertheless, this method suffers from several weaknesses, e.g. at depth discontinuities located near roof borders. The classical solution is to use a correlation method with adaptive windows [Kanade et Okutomi, 1994], but we propose an alternate solution which consists in post-processing the DEM obtained by correlation. This method is based on a combination of morphomath and anisotropic diffusion techniques, and uses the local contrast of the orthoimage to determine which image areas hooked on the correlation window.