How can I increase contrast on a multi-page PDF?
February 22, 2009 8:24 AM

How can I quickly and easily increase the contrast on every page of a PDF?

I have a PDF that is 200 pages long in which the paper rendered from the scan somewhat grey and some of the text from the opposite side is still visible. I know I just need to increase the contrast a little and it would taken care of. How can I do this? I have many PDF files like this so it's merely a test run.

I'm also hoping to remove some of the annotations someone made to the text before it was scanned. Other suggestions?

I'm on a Mac using Acrobat and and I've got Photoshop if it's absolutely necessary.
posted by Outis to Computers & Internet (6 answers total) 5 users marked this as a favorite
I haven't done this exact thing, Applescript, Automator, and Preview.app should be able to help.

I just loaded Automator and made a two step flow, Get Selected Finder Items and Apply Quartz Composition Filter to Image, in which I set the Color Controls to increase brightness.

Then I was able to save as an application, drag a file in, and the image inside got brightened.

I'm not sure how to step through each page of a PDF, but maybe someone else knows how.
posted by jragon at 8:35 AM on February 22, 2009


I've done this exact thing: Open one typical page in PS and see if you can fix it with Levels, by making what's light grey go white (click on various light greys with the white eyedropper), and what's black, stay black. (It's a typical problem with scanned double-sided text, often helped by placing a black sheet on top of the page being scanned to neutralize the bleed-thru). Once you find a good setting, open the next page and repeat while recording an action. Then select all your pages in Bridge and do a Batch process that runs your action on every page.
posted by dpcoffin at 8:59 AM on February 22, 2009


To get the pages out of the pdf, try this
posted by dpcoffin at 9:23 AM on February 22, 2009


Or Acrobat (not Reader), using Export…
posted by dpcoffin at 9:27 AM on February 22, 2009


If the annotations aren't fixed by the Levels adjustment, but are all in the margins, you could record your action so it also selects the margins and deletes the selection to white.
posted by dpcoffin at 9:35 AM on February 22, 2009


Thanks very much, all of you. I used the Automator method which is something I haven't used on my Mac after years of having one; the Quartz filters are pretty cool. Going to be using it frequently from now on.
posted by Outis at 6:14 PM on February 22, 2009


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