PistonDevelopers/rust-image — pull request #30 by ccgn (2014-06-15 00:25:53+00:00)
Title: Implement unsharpen masking

see:
https://en.wikipedia.org/wiki/Unsharp_masking#Digital_unsharp_masking

and

http://homepages.inf.ed.ac.uk/rbf/HIPR2/unsharp.htm

for details