feature request: enhance edge contrast in pictures

[lgasp]

To get better document pictures I suggest to implement an edge enhancement algotithm, that would also allow PNG compression of image if black and white.

Something like is implemented in open document scanner

By the way, this app works very well in detecting the edges of the document. thank you for the good work

[Breta01]

Thanks, that is definitely good idea. I will try to add this in next update.

If you want any contribution is highly welcome. I would try to help along the way.