An image filter based on nonlinear discontinuous partial differential equation (PDE) is presented. It models a class of morphological image filters called the level set method for gray image processing. We discuss the theoretical aspects of this PDE. The switch signal is controlled by the discontinuous right hand of PDE. We propose a discrete algorithm for its numerical solution and corresponding filter implementation. The study provides insights via several experiments. These types of filters are very useful in numerical image analyses. It is a class of morphological image filters called the level set method for gray image processing. We discuss the theoretical aspects of this PDE. The switch signal is controlled by the We propose a discrete algorithm for its numerical solution and corresponding filter implementation. The study provides insights via several experiments. These types of filters are very useful in numerical image analyzes.