Purifying your scanned PDF files

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© Lead Image © Sasin Paraksa, 123RF.com

© Lead Image © Sasin Paraksa, 123RF.com

Article from Issue 220/2019
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Having trouble reading that scanned PDF? You can add a little more contrast with some help from ImageMagick.

Gone are the days when you needed to go to the library for a book. Now you can download the book electronically, load it on your e-reader or tablet, and start enjoying it. But all electronic books are not equal. Particularly infuriating are electronic books that are actually scanned images of old print books. Scanned images of old books, which typically come in PDF format, are difficult to read on a black-and-white E Ink screen, where fading text and yellowing pages appear as blurs, blotches, and dark-gray backgrounds.

Luckily, you can clear up that blurry scanned image with a few tricks from ImageMagick. This article describes a method you can use to spruce up a scanned electronic book. Note: If you obtained the book from a lender or through another vendor, be sure the license supports this type of file manipulation.

Getting Started

I needed a copy of a sociology book, A Place on the Corner, by Elijah Anderson; the only place I could find it in electronic format was The Internet Archive. They had a scanned copy, so I loaded it on my Sony DPT-RP1/B e-reader, but the text was difficult to read (Figure 1). Dark spots appeared on the page, and the text was just a bit darker than the background, with poor contrast (Figure 2).

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