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I have a large PDF document that consists of scanned pages of a textbook. I want to run Adobe Acrobat 9's text recognition function on it, but I'm presented with this menu when I do.

Adobe Acrobat OCR Menu

I'm confused by the options in the highlighted menu. What option will produce the highest quality/most readable text? I thought 600 dpi implies a higher quality image than 72 dpi, so I'm confused by "High (72 dpi)" and "Lowest (600 dpi)."

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up vote 3 down vote accepted

The qualitative description of your options is referring to the amount of downsampling done to the image, not the resulting image quality. Downsampling to 72 dpi results in a high amount of downsampling.

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I don't know specifically for Acrobat, but many OCR programs are optimized for text in a "typical" sized body font at around 300 dpi. Start with that and try a page. If you get a lot of translation errors, try 600 dpi. If the page isn't clean, 600 dpi can make artifacts large enough to be interpreted as characters like punctuation marks, requiring more cleanup of the translation (most OCR programs don't know what dpi produced the image, they just see "mixed size fonts"). I would be surprised if 72 dpi works well unless you are translating huge fonts.

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