Image processing/enhancement algorithms for document OCR / readability?

Question

I'm looking for algorithms, papers, or software to enhance faxes, images from cell phone cameras, and other similar source for readability and OCR.

I'm mainly interested in simple enhancements (eg. things you could do using ImageMagick), but I'm also interested in more sophisticated techniques. I'm already talking to vendors, so for this question I'm mostly looking for algorithms or open source software.

To further clarify: I'm not looking for OCR software or algorithms; I'm looking for algorithms to clean up the image so it looks more readable to the human eye, and can possibly be used for OCR.

Answer 1

I had a similar problem when I was writing some software to do book scanning; floating around on the internet is a program called pagetools that does straightening of scanned-in pages using a fairly clever mathematical trick called the Radon transform.

I also wrote a small routine that would white out the blank space on the page; OCR algorithms tend to do a lot better when they don't have to contend with background noise. What I did, was look for light-colored pixels that were more than a small radius away from dark-colored ones, and then boost those up to being pure white.

It's been a few years, though, so I don't have the exact implementation details handy.

Answer 2

One simple image filter to look into is the "Median Filter" which is a very straightforward, easy to implement yourself, filter to help clean up scanned/photographed text. http://en.wikipedia.org/wiki/Median_filter