Recursive Implementation of Anisotropic Filters

Gaussian filter is widely used for image smoothing but it is well known that this type of filters blur the image features (e.g., edges). Two extensions of Gaussian filters will be discussed in this survey. One is the anisotropic filtering (bilateral filtering or PDE-based anisotropic diffusion) for feature-preserving smoothing and the other is the recursive implementation of various filters that can largely reduce the computational time in certain conditions. We will also discuss the combination of anisotropic filtering and recursive implementation for image smoothing such that the anisotropic smoothing could be done in a fast way.