An analysis of the Perona-Malik scheme

We investigate how the Perona-Malik scheme evolves piecewise smooth initial data in one dimension. By scaling a natural parameter that appears in the scheme in an appropriate way with respect to the grid size, we obtain a meaningful continuum limit. The resulting evolution can be seen as the gradient flow for an energy, just as the discrete evolutions are gradient flows for discrete energies. It involves, except at special isolated times, solving a system of heat equations coupled to each other through nonlinear boundary conditions. At the special times, the solutions experience gradient blowup; nevertheless, there is a natural continuation for the solutions beyond these singular times. (C) 2001 John Wiley & Sons, Inc.