I need a library for mostly color manipulation, I want to make a image become black and white, and augment the contrast, so that Tesseract (Google OCR library) can read better the images that I throw at it.
Or if someone has a better idea on how to improve Tesseract results, I am all for it.
Try OpenCV
http://sourceforge.net/projects/opencv/
Or imagemagick
http://www.imagemagick.org/script/magick++.php
or CImg, probably the easiest to use: no install it's just a header file.
If you do not want to use a big library you can code the algorithm yourself:
https://web.archive.org/web/20140825114946/http://bobpowell.net/image_contrast.aspx