This filter is used to automatically remove small defects due to dust, or scratches, on a scanned image, and also moiré effects on image scanned from a magazine.

Please note that this filter assumes that the text characters height is greater than 20 pixels by assuming the page image was scanned at least at 250 dpi. If there are character height lower than the previous mentioned height then this filter should not be used because it will probably remove good text parts.