Elliptic and Pseudo-Parabolic PDE System with Orientation-Adaptive Anisotropy

Abstract

In this paper, we consider a coupled system of nonlinear elliptic and pseudo-parabolic PDEs arising in anisotropic monochrome image denoising with orientation-adaptation. The system is derived from the minimization process of a nonconvex energy functional. In particular, we focus on the problem of determining the initial data for the orientation variable. In previous studies, a natural procedure for determining such initial data has not been sufficiently clarified. To address this issue, we introduce a formulation in which the time derivative of the orientation variable is removed. This formulation enables the initial orientation data to be determined implicitly within a time-discrete scheme. On the other hand, this formulation weakens the conventional energy-dissipation structure and leads to new difficulties in constructing a stable variational time-evolution process. To overcome this issue, we develop an analysis based on a time-discretization method and establish the well-posedness of the proposed system, namely existence, uniqueness, and continuous dependence, as well as an energy-inequality. We also show that the proposed time-discrete scheme determines the initial orientation data consistently with the continuous model. These results provide a mathematical framework for the initial-orientation determination problem in orientation-adaptive anisotropic models.