Converting PDF to bilevel (automatic solution)

[Lower Case]

I have a 600 page PDF document (it's a scanned book) with a colour cast (brown text on yellow). What is my best approach to getting black text on white? I have been playing with the Convert Colors... feature in Acrobat 8 Pro without success. Is there some sort of extreme colour profile I can apply to increase the contrast?

This won't be color separated so it doesn't absolutely need to be 100% K in the text, but just to lighten up the yellow background enough to make it invisible.

Obviously I could do a few pages with the Touch Up tool and Photoshop, but don't fancy going through 600.

 

[almaink]

If all the pages are scans, then export all images from Acrobat, and run a batch convert on that folder from Photoshop, converting all to bitmap using 50% threshold. Then use InDesign to remake the PDF from the folder using the import multipage PDF script.

 

[buckeye]

What dpi were they scanned at?

 

[Lower Case]

Thanks everyone. The scans are only 150dpi, but that doesn't matter as it's only one working copy I want to print – it's not a commercial job. It's getting rid of the colour cast that's the issue. I will go the export, batch process, and recombine route.