Holes and scratches

6

This is pre-processing step for noise reduction. Every pixel with Ink bit set, is tested for neibours with Paper bit set, like in  Conway's Game of Life . If six or more bits are Paper, then that Ink is replaced with Paper. Same is with opposite situation (Paper surrounded with 6 or more Inks is replaced with Ink). So the small errors are corrected. The ball on the photo is relatively new, so it is hard to see the effect of this step here.