Median Filter:
Which is also called Non- linear filter or order-static filter because there response is based on the ordering or ranking of the pixels contained within the mask?
The steps to perform median filtering are as follows:
1) Assume a 3x3 empty mask.
2) Place the empty mask at the left hand corner.
3) Arrange the 9 pixels in ascending or descending order.
4) Chose the median from these nine values.
5) Place this median at the centre.
6) Move the mask through out the image.
Thus, in median filtering, the grey level of the centre pixel is replaced by the median value of the neighborhood.