Photoshop Curves
http://community.wacom.com/en/inspiration/blog/2014/september/how-to-bend-photoshop%E2%80%99s-curves-and-levels-to-your-will/?utm_campaign=FY15-8100-20-Photography-Tutorial-Beginner&utm_source=facebook.com&utm_medium=cpc&utm_content=How_to_Use_Levels_Curves
Best Practices for Scanning
http://talkingpdf.org/key-best-practices-for-document-scanning/