Combining bidirectional flow equation and fuzzy sets for adaptive image sharpening

In this paper, a region-based fuzzy bidirectional flow process is presented for image noise removal and edge sharpening. An image is divided into three-type different regions according to image features: edges, textures and details, and flat areas. For edges, a shock-type backward diffusion is performed in the gradient direction to the isophote line (edge), incorporating a forward diffusion in the isophote line direction; while for textures and details, a fuzzy backward diffusion is done to enhance image features preserving a natural transition, Moreover, an isotropic diffusion is used to smooth flat areas simultaneously. Finally, a shock capturing scheme with a special limiter function is developed to speed the process with numerical instability. Experiments on real images show that this method produces better visual results of the enhanced images than some related equations.