Vector Median Filter
Median filters are a popular way to restore an image that has been corrupted by noise. For a color image, it is common to apply the filter separately to each channel and then to combine the individual results. However, this approach usually introduces false colors and degrades edges. Vector median filters, which operate on pixel values, do not have these defects.
J. Astola, P. Haavisto, and Y. Neuvo, "Vector Median Filters," Proc. of IEEE, 78(4), 1990 pp. 678–689.