Dear David,

you might want to look at LocalAdaptiveBinarize and in particular the first example of the Applications section. There is also this example. Another important factor is that the scanned page is properly aligned. If the text is slightly distorted or rotated OCR will be problematic. It has been reported that changing the alpha channel might also help.

I also found this discussion helpful.

You are saying that the background is not uniform. If LocalAdaptiveBinarize does not help you might want to use RemoveBackground to preprocess the images.

As Sean said, an image that has a similar problem would help a lot.

Cheers,

Marco