Image sharpening via Sobolev gradient flows. (English) Zbl 1202.94019

Calder, J.; Mansouri, A.; Yezzi, A.

SIAM J. Imaging Sci. 3, No. 4, 981-1014 (2010).

Summary: Motivated by some recent work in active contour applications, we study the use of Sobolev gradients for PDE-based image diffusion and sharpening. We begin by studying, for the case of isotropic diffusion, the gradient descent/ascent equation obtained by modifying the usual metric on the space of images, which is the \(L^2\) metric, to a Sobolev metric. We present existence and uniqueness results for the Sobolev isotropic diffusion, derive a number of maximum principles, and show that the differential equations are stable and well-posed both in the forward and backward directions. This allows us to apply the Sobolev flow in the backward direction for sharpening. Favorable comparisons to the well-known shock filter for sharpening are demonstrated. Finally, we continue to exploit this same well-posed behavior both forward and backward in order to formulate new constrained gradient flows on higher order energy functionals which preserve the first order energy of the original image for interesting combined smoothing and sharpening effects.

MSC:

94A08	Image processing (compression, reconstruction, etc.) in information and communication theory
35A01	Existence problems for PDEs: global existence, local existence, non-existence
35A02	Uniqueness problems for PDEs: global uniqueness, local uniqueness, non-uniqueness
35A35	Theoretical approximation in context of PDEs

Keywords:

image diffusion; partial differential equations; gradient descent; gradient ascent; Sobolev spaces; image sharpening