Random-valued impulse noise removal in color images by using switching Non-local vector median filter

This paper describes a novel image filtering method for removal of random-valued impulse noise superimposed on color images. In color image filtering, generally, it is preferable to deal with the R, G, and B components of each pixel of a color image as elements of a vectorized signal as in the vector median filter rather than component-wise signals in order to prevent color shift after filtering. Furthermore, in impulse noise removal, it is essential to use switching type filtering manner as in the switching median filter to preserve the detailed part of an original image with good quality. By taking those fundamentals in consideration, in this study, we propose a switching-type vector median filter with non-local processing mainly consists of a noise detection part and a noise removal one. Concretely, we propose a noise detector which proactively finds out noise-corrupted pixels by focusing attention on isolation tendencies of pixels of interest in difference images between RGB components. Furthermore, as a noise removal filter, we propose an extended version of Non-local median filter (NL-MF), which we proposed previously for grayscale images, named Non-local vector median filter (NL-VMF) which deals with color images. The proposed method realizes superior balance between the detail-preservation based on the proactive noise detection and the noise removal by the non-local switching vector median filtering. The effectiveness and the validity of the proposed method are verified by some experiments using natural color images.