Abstract From the analytical description of linear image contrast in high-resolution electron microscopy (HRTEM) a simple relation between characteristic defoci belonging to characteristic image patterns and specimen properties is given. This offers a possibility to determine the specimen thickness H from the knowledge of the local defocus Δf. At interfaces it suffices to know the difference Δ(Δf) between defoci belonging dto characteristics image patterns in the two materials. From this difference even the local defocus Δf can be obtained. The analytical description of linear imaging also offers a simple method to find “appropriate” imaging parameters for obtaining characteristic contrast patters. This is very helpful for the chemical mapping of interfaces. Furthermore, nonlinear calculations are also performed for quantitatively testing the linear description of image contrast. They show that the linear description is in most cases sufficient to identify the defoci belonging to characteristics image patterns. But even when this does not apply, there still exists a direct relationm between in this case the belonging defoci of nonlinear characteristic image patterns and the specimen thickness H.