How can I remove yellow background from scanned PDF?

I have scans of some very old books that I would like to have printed out for my use (they are out of copyright), but because the pages are yellowed from age, the printouts have a grey background.

The scans are in PDF format, and I cannot request a re-scan in black and white.  I cannot convert the text alone, as this book features illustrations on every page which are intertwined with the text.  And the fix cannot be a print function fix, as I will be uploading the file to have it printed in book form.

I have tried several different methods: I downloaded a free trial of Pitstop Pro and used that to try and replace the yellow color with white, but because the pages are so many different shades of yellow/brown, I was getting pages with splotchy whitish areas...and no amount of fiddling with it would bring it to anything approaching all white.

I tried doing the same thing after converting it to Device grey, but the same thing happened.  I couldn't get rid of all the grey.

So then I tried sending it through Photoshop and running a threshold filter on it.  This helped, but the file was so unbelievably huge when I was done that I couldn't use it.  I tried to reduce file size in Acrobat, but it did very little good.

Is there any way of solving this within Adobe Acrobat 9 Pro?  Or of using Photoshop without the file size ballooning out of control?
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Adobe Optimise scanned pages may work, but can you upload 2-3 pages with varying background to check,

difficult to guess in the dark...

roma247Author Commented:
Actually, I did try that, but it did very little, I'm afraid.

I'm attaching a few pages in case they help.

This is indeed weird as for some reason the Optimise scanned PDF f=unction of Acrobat refused to work.

I have run some output options on Acrobat omitting colour plates and only running the black plate,  the resulting b&w image could be optimised and the background is now white.

BUT, this has resulted in a very poor quality document which you cannot use for printing at all. And there are still artefacts left around some type and pictures.

As it stands there is no option to remove the background without affecting the text. The text is part of the background image as far as any automated optimisation is concerned and the setting will either leave too much marbled background or remove too much of the text.

I suspect you can do this manually in Photoshop on a page by page basis, but at that rate you may as well OCR and retype set it in Indesign with the pictures clipped from Photoshop.

You could play around with the settings in Acrobat and see if you get a better result. Here is what I have done:

Print as new PDF > Print as Image. Discard CMY plates in Advanced > Output
Ran Optimise Scanned PDF from Document menu using default settings => still marbled bg
The same with most aggressive setting => see attached results.

The only other alternative is to print as is and use the yellow or convert to B&w and live with the marbled bg...



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roma247Author Commented:
Yes, what you are describing is very similar to my experience.  It sounds like my best bet is to post a separate question under Photoshop, trying to find if I can compress the ones that I used the threshold filter on to a usable size.

Thank you so very much for the time you took to give this a try.

If anyone else finds this question and has any other suggestions, I will continue to monitor this...

I know it may sound simplistic but sometimes I find I get the best results with the simplest of adjustments.

I did the first page as an example of my results.

All I did was narrow the levels and then push up the contrast a bit.

Take a look at the dialog boxes below to see the values I used.

I hope this works for you.
roma247Author Commented:
Hi SaigonJeff,

Sorry for the delayed response...

I like the idea, as it does a nicer job with the grays than just running the threshold filter.  There were still some minor artifacts after running those two, but converting to Black and White took care of them.  Looks pretty good.

Unfortunately, the problem I'm having with the Photoshop PDFs is that they're so obscenely large, I can't upload them to the publisher.  I'm still trying to find a solution for that problem; I've tried refrying them using the print function in Acrobat, but it only cuts the file size in half...which helps, but still too big...

Anyway, thanks very much for the tip, because even though it didn't solve my problem, it still helped.

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