Previously we have presented a selective sharpening method for monochrome images. Our method is based on the simultaneous nonlinear reaction-diffusion time-evolution equipped with a nonlinear diffusion term, a reaction term and an overshooting term, and can sharpen degraded edges blurred by several causes without increasing the visibility of random noise. This paper extends our method to selective sharpening ofcolor images. As to the how to extend it, we take into accounts two variations about the treatment of three color components and the selection of the color space. By experiments, we quantitatively evaluate performance of these variations. The best performance is achieved by the collective treatment of color components based on the simultaneous full-nonlinear reaction-diffusion time-evolution, and blurred color edges are sharpened selectively much better than by the existing methods such as the adaptive peaking melhod.
SUMMARYThe authors describe a technique for selectively sharpening only edges that were blurred due to various causes without making interference factors such as random noise more conspicuous. The selective sharpening technique described in this paper is implemented as an iterative updating nonlinear algorithm obtained by discretizing a type of nonlinear reaction-diffusion time-evolution equations. The update terms of this algorithm consist of a quadratic nonlinear smoothing term, reaction term, and overshooting term. By performing quantitative evaluation experiments, the authors showed that the proposed technique has significantly better selective sharpness enhancement capabilities than existing sharpness enhancement techniques such as the peaking method. In addition, the authors introduced a processing parameter adaptive control method in the proposed technique and applied it to the suppression of breathing distortions in video sequences. Breathing distortions, which are video sequence distortions that often appear in old films, are time-varying blurring distortions that occur due to temporal variations of the focus.
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