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Old 12-08-2008, 08:56 AM   #1
Ammon
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Scanning pages: how many dpi to convert to PDF?

At what resolution should I scan pages, have adobe acrobat pro to convert to pdf, there's photographs aswell as text? thanks
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Old 12-08-2008, 09:30 AM   #2
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It depends what you want to do with the resulting PDF file. If you want to print it, ideally it should be scanned at the full resolution of the printer - 600dpi (or whatever). If you simply want to view it on the screen, 150dpi will probably suffice.

Best thing to do is experiment and see what works best.
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Old 12-09-2008, 02:01 PM   #3
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a) OCR minimal should be always your moto.

B&W - 300 dpi.
Grey - 300 dpi (compressed after to 200 dpi in Acrobat, or scan at 200 dpi from the start).
Colour - 200 dpi.

b) Then it all has to do with the type of PDF you are creating:

1 - image pages…
2 - image pages with text under the images…
2 - text with images in it…
3 - just text...

You see, contrary to what most of the people say (know…) there is not just PDF but several types of PDF’s… and to let you know the best solution one must know what type of PDF’s you are needing.

Anyway, even not defining that, the first advise a) will resolve most of your problems.

Best digitizing,
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Old 12-17-2008, 05:59 PM   #4
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I'll add that, for small text (like footnotes) or intricate diagram pages/books, scanning at 400 dpi greatly improves the OCR. If OCR accuracy is very important, and you don't want to spend many hours proofreading, higher resolution scanning helps a lot.

And takes more time, and eats more memory. 300 dpi provides good OCR; it just has problems with very small text, broken text like faxes or 3rd-gen photocopies, or odd fonts like some older books have.
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Old 12-28-2008, 03:16 PM   #5
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Most text I've done was on 300dpi, and worked pretty fine.
300dpi for clean scans, higher if the pages are yellowed out, it has images, or if it uses non-standard letter types.
200dpi works, but you'll have lots more trouble with correcting OCR errors.

72dpi in 3bit (8 tint) greyscale png I'd recommend as smallest scan for reading a book. It's not good enough for OCR though...

The needed DPI also depends on the font size of the printed (original scanned) page.

Last edited by ProDigit; 12-28-2008 at 03:19 PM.
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