ReduceNoiseFilter
This filter reduces noise in an image. It compares each pixel with its eight neighbours and if the pixel is larger or smaller in value than all eight, replaces it by the largest or smallest of the neighbours. This is good for removing single noisy pixels from an image.
In this example I've added some ridiculously obvious noise to an image and removed it with the ReduceNoiseFilter filter.
ReduceNoiseFilter: Before and After