The research paper "Multidirectional Scratch Detection and Restoration in Digitized Old Images" says that,
4.1. Preprocessing. The preprocessing step aims to enhance image features along a set of chosen directions. First, image is grey-scaled and filtered with a sharpening filter (we subtract from the image its local-mean filtered version), thus eliminating the DC component.
Now, I am Googling the term "Local Mean Filter" but there is nothing available like that.
Can anyone please provide me any reference of "Local-Mean Filter"?
What filter are they using for Sharpening?